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e for International Agricultural Research (ACIAR) was
82 by an Act of the Australian Parliament. Its mandate is to
al problems in developing countries and to commission
between Australia and developing country researchers in
as a special research competence.
are used this constitutes neither endorsement of nor
any product by the Centre.
lelAR MONOGRAPH SERIES
eries contains the results of original research supported
deemed relevant to ACIAR's research objectives. The series
ionally, with an emphasis on the Third World.
or International Agricultural Research, GPO Box 1571,
1
P., ed., 1992. The giant clam: an ocean culture manual.
No. 16, 68 p.
laid out by Arawang Information Bureau Pty Ltd,
.
t Pty Ltd.
The ocean nursery
2.1 Site selection
2.2 Intertidal ocean nursery
2.3 Subtidal ocean nursery
Preparation of clams for ocean nursery
Substrates
Estimating number of clams
Stocking with juvenile clams
Transport
Measurement of juveniles
Records
Monitoring
Growout phase
4.1 Transport to growout site
4.2 Site selection for growout
4.3 Sources of juveniles
4.4 Transport
4.5 Arrangement of clams in growout area
4.6 Monitoring
2
3
4
3.1
3.2
3.3
3.4
3.5
3.6
3.7
7
Introduction
1.1 Identification of giant clams
1.2 Importance of giant clams
1.3 Culture of giant clams
1.4 Floating ocean nursery
1
37
38
38
38
38
39
37
31
32
33
34
34
35
36
31
19
22
24
19
7
8
8
15
4
5
6
Ust of contributors
Preface
Acknowledgments
Contents
7
6
5
Appendix
Recorded growth
References
Economics and
7.1 Markets
7.2 Whether to
nursery
7.3 Production
Diseases and p
Summary
giant clams
6.2 Preparation
6.3 Quarantine
giant clams
6.1
Predators and
Predators a
Predator co
Biological c
5.1
5.2
5.3
utors
Hilconida P. Calumpong, Silliman University Marine
Laboratory, Dumaguete City 6200, Philippines.
Jojo Legaspi.
Identification, Ocean Culture
Silliman University Marine Laboratory, Dumaguete
City 6200, Philippines.
Zoology Department, James Cook University,
Townsville, Queensland 4811, Australia.
Silliman University Marine Laboratory, Dumaguete
City 6200, Philippines.
Marine Science Institute, University of the
Philippines, Diliman, Quezon City 1101 , Philippines.
Marine Science Institute, University of the
Philippines, Diliman, Quezon City 1101, Philippines .
Intemational Center for Living Aquatic Resources
Management (ICLARM) , Coastal Aquaculture
Center, p.a . Box 438, Honiara, Solomon Islands.
ICLARM Contribution 794.
Silliman University Marine Laboratory, Dumaguete
City 6200, Philippines.
eries
es and wire-reinforced cement substrates
Clem Tisdell
Chapter 7
John Norton
Chapter 6
Hugh Govan
Chapter 5
Department of Economics, University of
Queensland, Australia 4072.
Economics
aonoonba Veterinary Laboratory, Townsville, p.a.
Box 1085, Queensland 4810, Australia.
Diseases and Parasites
ICLARM Coastal Aquaculture Center, p.a. Box
438, Honiara, Solomon Islands.
(ICLARM Contribution No. 747)
Predators and Predator Control
Prelate
This manual provides a guide to the practicalities of giant clam a
nursery culture operations (see Figure 1.2, page 14). A compani
details the hatchery and land nursery culture of the giant clams.
The markets for giant clams are at present almost exclusively in
demand is for adductor muscle, mantle (fresh, dried, frozen) and
required on marketing aspects, the general indication for future
clam cultivation is positive.
The giant clam represents a traditional food source for the peopl
demand for the meat or shells, coupled with the over-exploitation
and locally exterminated populations of some species. Thus, in t
the reproduction and larval culture of giant clams became impor
Demonstration Center (MMDC) in Palau played a key role in mo
the laboratory to mass culture. The University of Papua New Gui
Centre) was likewise involved in giant clam larviculture, but on a
early to mid 1980s, Australia became involved with giant clam m
government-funded project through the University of New South
project funded by the Australian Centre for International Agricult
administered by James Cook University of North Queensland. T
began with Australia, Fiji, Philippines and Papua New Guinea but
included Tonga, Cook Islands, Kiribati and Tuvalu, while losing P
1980s, the International Centre for Uving Aquatic Resources Ma
aquaculture centre near Honiara, Solomon Islands in which giant
cultured. Other ha~cheries and ocean nurseries have been starte
recently in Tonga and Cook Islands.
edgmen,s
product of research in eight countries: Australia, Cook
, Philippines, Solomon Islands, Tonga and Tuvalu. The
nded by the Australian Centre for International
ch through projects 8322 and 8733. The research was
art by the Australian International Development
(AIDAB) .
buted to the writing of this manual. The information
y Dan Bonga (UP-MSI), Lourdes Y. Fabro (SUML),
nes Cook University), Rio Abdon-Naguit (SUML) and
MSI) is gratefully appreciated. Additional editing was
o Gomez and Suzanne Mirgon (UP-MSI) and Dr John
Roy de Lern and Pacito Roberto helped in the
manuscript.
butions to this volume were funded by the Canadian
e for Ocean Development (floating ocean nurseries)
ion studies) and accomplished with staffing support
ngdom Overseas Development Administration,
nd for Technical Cooperation, U.K. Voluntary Service
U.S. Peace Corps.
Chapter
Infrodu,fion
J
Identification of giant clams
Identification is facilitated by knowing the differences between th
Tridacna and Hippopus . Differentiation of these two genera is b
There are eight known species of living giant clams. These speci
shell characteristics (such as presence and absence of scales), r
adult clams on reefs .
,. 1
Giant clams have two main parts, the shell (which can be used f
species) and the soft flesh which is covered by the mantle (the
mantle has an elongate incurrent aperture and a round excurrent
the clam's gills. Beneath the mantle are the different organs, incl
adductor and retractor muscles, digestive tract, gonad, foot and
external and internal parts of a giant clam.
Aside from achieving great proportions, giant clams are unique b
symbiotic algae, called zooxanthellae, which supply food to the c
Therefore, giant clams have their own built-in 'food factories' whi
carbon dioxide as basic raw materials. They also filtE:r microscop
their gills, like other bivalve molluscs (oysters, scallops, etc.).
Giant clams (Tridacnidae: Bivalvia) are the largest bivalves in the
waters of coral reefs around countries in the Indo-Pacific region like
Malaysia, Palau, northern Australia and the Philippines (Rosewater
CLAMS
mantle. In Hippopus species, the area of the byssal orifice
Tridacna species, teeth are absent. Additionally, the mantle of
colours and projects laterally beyond the lip margin of the shell,
is usually dull and limited within the shell margin. A rare
oa, is somewhat transitional in these characteristics. The
nt clam are described and illustrated in Boxes 1.1-1.8. A key to
m species is shown in Box 1.9.
giant clams
e diet of island and coastal peoples of the Indo-Pacific region.
le except for the kidneys, which are bitter. The adductor muscle,
e entire flesh, is most sought after. This is the large muscle which
ally for a variety of purposes (sinks, ashtrays, soap cases, house
t items as souvenirs in the tourist trade, for shell and stone craft
t clams
nt clams have been severely reduced in many areas by
f extinction. Clam culture provides (1) food to coastal
m raw materials for new industries; (3) a means to restock coral
te reef conservation.
, giant clams have been the subject of intense studies at
lippines, Solomon Islands and elsewhere in the Pacific.
S I PHON
l NCURRENT
GILLS
TEETH-
RIB----...
BYSSA L-OR IFICE
Figure 1.1
@
©
EXCU RRENT
SIPHON
MAN TLE
KIDNEY
HEART
GONAD
MUSCLE S
f\ DOUC TOR
AND PEDAL
RETRACTOR
---SCUTE
VALV ES
--HINGE
---UMBO
-,
' - -- - --
'-
Parts of a giant clam . A. Dorsal view.
B. lateral view showing the internal
organs . C. lateral view of shell.
Distribution: Known to be previously distributed more wide~ in the Indo-Pacilic region but now restricted through
overlishing to Austrat.a (Great Barrier Reef), Indonesia, Papua New Guinea, Philippines (Palowan and Sulu Sea),
Solomon Islands and parts of Micronesia.
Distribution: Australia (Great Barrier Reef), Pacific Islan
Guiuon, Somar; Scorborough Shoals, South China Sea; lub
Habitat: Occurs on outer edges of reels at about 4-20
fringing reels adjacent to large island masses.
Juveniles of T. Jerasa and T. gigas are also simUar in appe
on its shell surface. Also, the mantle of T. Jerasa is almost
gigas is usual~ drab (yenowish brown to tan).
TriJacna Jerasa is often confused with another species, H.
rounded hp margin. However, the byssal region is heart-sh
D.scriptlon: Second largest species, reaching 50 cm or m
the ~p margin rounded; shell thick and heavy.
H.itat: Generaly found on sand and among corals on shallow reels but may be found at depths of 20 m; some
individuals may be exposed during low tide.
CDIIIIIIOII lame: Smooth giant dam
A. lateral view. B. Ventral view.
Description: largest spe<ies, attaining lengths of over 100 cm and weights of 200-500 kg; she" while in colour,
fan-shaped (side view) with deep grooves; edge of the sheHs bear elongate, triangular projections.lcrge individuals
are unable to dose their sheHs completely because of the weI~developed mantle.
IOcm
Trmacna Jerasa
CoInIllOllIaIll: True giant clam
o
Box 1.2
ScIentific name: TriJocllO Jerasa
A. lateral view. B. Ventral view. CMantle view. D. Do~ view.
TriJocna gigas
Scientific 1ICIIIt: TriJoC/IQ gigas
Box 1.1
CLAMS
o
CMontle view. D. Donal view.
c
ID em
with wide~ spaced Ruted stoles which becomelofger
e may be white, tinged with lemon yellow lowards the
oves, or just plain yelow or orange. This spedes is
oceal by lhe presence of well spaced stoles from the
rubble at depths up 10 18 mon reefs usuol~ dominated
Frenth Polynesia.
Ioxl.4
Bongated dam
'-" .
-·f ' .. .. /
....
:::.-
( !.
..• - --~ ~ .-"
--" , ~.,~ ). ~ "r~:'
~. ' \i) ~ r·:':\.
~<wZ~~~~. ~
~\....
~~'~ '"
~ ~~{~~~~~~i~
)
-...- -..
~
· ·· ·~c
" -_ _~5'm
~"L ;~'~ i i' : :~.::'ty
A. Laleral view. B. Ventrol view. CMande view. D. Dorsol view.
TriJacna maxima
(0lIIIII01 IGIIIt:
ScieIIlifk 1ICIIIr. TriJocno maxima
Dtsaiplion: Can reach 35-40 cm in length but is usuaHy mlKh smaHer; brighl mande colouring; shell is elongated
at one side with dose~ spaced stales near Ihe mergin; shell colour varies from plain while 10 yellow or white tinged
with orange.
HalMlat: Partly embedded in carol or firmly aIIoched 10 coral heads.
Distn"bulion: Found from Eosl Africa ond the Red Sea 10 French Polynesia.
Scienlifi< name: Tridocna tevoroo
lloteral view.
B. Ventn~ view.
Distribution: Widespread and (ommon in the Indo·Maloy and western Pacific regions, from Thailand to New
Caledonia.
Habitat: Burrows into (oral boulders on the reef·top; on~ shell margins and manrle ore visible.
Distribution: Re(orded only from Tonga and the eastern
Habitat: Found at moderate depth (14-30 m) in clear o(
reefs.
Dtsaiption: Rela~vely lorge, reaching more than 50 (m
thi(kenings and dark red bands at umbo, upper shell margi
sim~or to T. derasa; mantle with numerous warty projectio
popiHoe around inwrrent siphon.
om
TriJacna tevoroo
Dtsaiptioa: Smallest species reaching on~ 15 (m in length; sheH white often ~nged with pinkish-orange or yellow
both inside and outside; usuol~ quite smooth except for closely spa(ed scales near the upper edge of shell; monrle
usuol~ brighrly (oIoured like T. maxima but (an be dilferen~ated in having 0 strong~ triangular ovate shell (lateral
view) and very wide byssol orifice (ventral view).
B. Ventral view. C. Mantle view. D. Do~1 view.
~_ _ _ _--=5
c
Box 1.6
Common name: Tevoro (lam
llateral view.
TriJacna suoceo
Scientific Hme: Tridocna aoceo
(OIIImoII Hmt: Boring clam
Box 1.5
CLAMS
~
_ __ _ _,,-,,o cm
C Mantle view. D. Danol view.
Box 1.8
Hippopus porce/Ionus
"--_ _ _--,,,
10 cm
A. Lateral view. B. Ventral view. C. Mande view. D. Donol view.
Common name: China dam or porcelain clam
ScientifK name: Hippopus porcel/onus
oof dam, bear's paw dam
Desalption: Thinner IIld smoother shell thon that of H. hippopus, usual~ lacking the strawberry colouration. The
mantle is olive green. H. porce/Ionus can be easi~ distingUished from H. hippopus because the incuITent siphon
possesses popillae or fringing tentacles.
Distribution: Rare, and restricted to the Sulu and South (hina Seas, Philippines and Palau.
Habitat: Occurs in sandy portions of coral reefs.
y, IIld elongate to triangular in shape with minute stales
s brown, dull grey or green in colour.
to 6 mand on seograss beds adjoining reefs.
from Tha~and to Vanuotu. Retendy extinct in Fiji, Samoa
Key 10 the gianl clam species (from Lucos el rJ. 1991)
4(3)
3(1 )
2( 1)
Shell length usually > 500 mm; upper shell region with scutes or eroded scutes; hinge equal to or less
than half shell length ............................................................................................. 6
Shell length up to 500 mm, occasionally larger; upper region of large shells plain, without scutes or
strong ribs; hinge usual~ longer than half shell length ..................................... ...... 5
Shell length rarely> 550 mm; without elongate ; interdig~a~ng projections on each distal shell
margin; manrle variab~ coloured, without iridescent blue-green circles .................... 4
Shell length of large specimens> 550 mm, some~mes greater than 1 m; with about four elongate,
interdig~a~ng projections of each dislal shell margin, being most elongate and acute in large
specimens; shell withoutscutes, except for some tubular projections near umbo in very small
juveniles; manrle brownish, with numerous iridescent blue-green circles ................... T. gig05
Shells in specimens less than about 200 mm shell length not thick nor strongly ribbed and with on~
faint reddish blotches; incurrent apertures with guard tentacles (papillae) ................. H. porcellanus
Shells thick and strong~ ribbed, with reddish blotches in irregular bonds; incurrent apertures without
guard tentacles (papillae) ....................................................................................... H. hippopus
Byssal orifice of opposed valves without interlocking teeth; no dis~nd ventral region of shell ourlined
by prominent radial ribs; manrle, when ful~ extended, usual~ projecting lateral~ beyond shell
margins .........................................:....................................................................... TriJacno ... 3
Byssol orifice region of opposed valves with inte~ocking teeth; dis~nct region of shell around byssal
orifice, ourlined by ventral-most pair of prominent radical ribs; manrle, when ful~ extended, not
projecting lateral~ beyond shell margins .................................................. .... .......... Hippopus ... 2
There are now eight extant species of giant clams and the key to species given by lucas (1988) needs to be
expanded and modified to incorporate T. tevoroo. See Figure 1.1for the location of the various parts of the
clam used in the key.
Box 1.9
7(6)
6(4)
5( 4)
Shell length of large specimens often> 150 mm; shell
view; byssol aperture moderately wide to wide; scutes
partial~ embedded in reef substrate .........................
Shell length <150 mm; shells not strong~ osymme
wide; scutes eroded away except near shell margin
...............................................................................
Shells usual~ asymmetrical about umbo in lateral vie
low and often eroded, set close together both within r
moderate~ wide to wide; embedded or part~ embed
aperture with indis~nct guard tentacles .....................
Shell approximate~ symmetrical about umbo in late
large and well·spaced both within and between the r
rows usual~ about some 05 scute width; byssal apert
substrate; manrle usually of subdued and monied co
................................... ..................... .......................
Rib-like radial folds on shell usual~ striped with colou
incurrent aperture with conspicuous guard tentacles ..
Rib-like radial folds on shell without coloured patches;
inconspicuous guard tentacles ..... .... .... .... .... ..............
lAMS
iSPERM
\lOG
~~
~
•
~
~ ~ ~...
___ ....
VELlGER
am culture: the hatchery, the nursery, the ocean nursery and
©
'& ) I
EGG
TROCHOPHORE
Larval rearing
and nursery
quaculture of the giant clams
Figure 1.3
Different designs of Roating cages used
at the Coastal Aquaculture Centre (CAC),
Solomon Islands.
Hatchery and nursery pha,e,
Ocean nursery and growout phase,
Each catamaran has a polypropylene rope bridle with shackles
The current designs are shown in Figure 1.3A-C. The essential c
150 mm PVC drain piping with endcaps which provide the buoy
crosspieces to form a catamaran. Stainless steel strapping was i
catamarans. However, heavy monofilament nylon fishing line is
structure has relatively high rigidity, can withstand moderate sea
sheltered lagoonal waters which are envisaged as primary sites f
In the Solomon Islands, at the ICLARM Coastal Aquaculture Cen
clams are transferred to floating ocean nurseries where they are
transfer to benthic cages.
1.4 Floating ocean nurseries
The ocean nursery phase of giant clam culture is discussed in so
growout stage is described in Chapter 4.
1.3.2
In the land-based nursery culture, newly settled juvenile clams ar
seawater and aeration. Here, they are allowed to grow to approxi
either allowed to grow to marketable size or transferred to the oc
information on hatchery and nursery culture, please refer to Bral
The hatchery phase includes: (I) induced spawning of giant cla
suspension or serotonin (neurotransmitter); (2) hatching of eggs
(3) rearing of clam larvae in larval tanks for 1-2 weeks; and (4)
either in land-based tanks or floating ocean cages (see section 1
1.3.1
CLAMS
ng system which consists of individual anchor blocks, chain and
e length (2.5 x depth) of heavy nylon line.
ment-based trays in various configurations; either as individual
) suspended from hardwood poles (Figure 1.3A), as platforms
ich small (0.42 square metres) trays a re individually attached
box in which two or three trays are deposited (Figure 1.3C).
in various locations, including the relatively exposed waters
hoppy waves of around 0.4 m height are often experienced on
d areas there is an obvious opportunity for using bamboo floats,
y-<:oated. In relatively deep water (>3 m) it is unnecessary to
tray. Despite the fact that the hardwood cross bearers are
ntered with shipworm (Teredo sp.s) and it is necessary to paint
nurseries appear to be areas of shallow sandy sea floor or
e of exposure to wind-induced waves and good water exchange
tidal amplitudes. The deSigns shown in Figure 1.3 have
and will suffer few gear failures provided they are regularly
venile clams by submerging the trays in raceways or tanks and
eniles per square metre. The juveniles are left undisturbed for 48
al attachments, whereafter they can be moved offshore.
vere losses of juveniles if they are exposed to moderate wave
ed.
ular checks for predators, principally Cymatium species and
fouling organisms which can clog the meshes and reduce
Juvenile clams can be grown in the floating nurseries until they a
on their location and degree of exposure, and then transferred to
be possible to retain them in floating cages until they attain a siz
in enclosures or exclosures.
There is no difference in the mortality rates of juvenile clams in u
floating ocean nurseries. However, there is a dramatic change in
ocean, with the juveniles in the floating ocean nurseries attaining
point they can be transferred to benthic ocean nursery cages.
water exchange within the tray. Algal overgrowth can be reduced
simply fanning the bottom of the tray and wafting away the unw
such as Cerithium species, will also reduce algal growth.
Chapter
If a protected area with moderate current is found, clams can be
The exposure during extreme low tides minimises the need to cl
retarded by direct exposure to sunlight. Excessive exposure to su
Shallow depth of water. Ocean nurseries can be placed on eit
too deep «10 m) portions of the inshore environment. These are
the lowest low tide.
Sites that have the follOwing conditions have been found most su
of clams.
2.1 Site selection
The length of time that juveniles stay in the ocean nursery (befor
dependent on the clam species and the conditions of the ocean
2.1 illustrates an ocean nursery.
The culture site may be subtidal or intertidal. T. gigas and H. hip
while T. derasa and the rest are best grown in shallow subtidal si
culture is that it is relatively accessible and easy to maintain. The
exposure during tropical cyclones (typhoons) and accessibility t
The ocean nursery phase in the culture of giant clams begins wh
to the sea in protective mesh cages. They are caged for protectio
size' (about 20 cm) is reached.
Tlte olean nursery
2
CLAMS
y kill the clam, or if the clams survive, the shells tend to become
idal ocean nurseries have limited application in the Philippines,
as for docking and other needs. Also, these areas may be
monsoon trade winds.
'* c=
~
<""-
~ CI~;>
- ""t
.~
n nursery somewhat deeper where wave action is minimised by
must be good (3-7 m) to ensure optimal illumination for
possible areas (arrows) within the coastal environment where
ery
Figure 2.2
j
_
~O w_ll ~e ~Y! I _
HI;'" lid!! h!!vel
_
possible areas (arrows) where an ocean
nursery may be established.
----t- --- r-
~~
Sea bed with few or no predators. To ensure clam survival, a
be chosen. Coral reefs, although natural habitats of clams, have
Areas with slow circulating water (as in deep bays) are not advis
substrate of bays is usually mud and light penetration is correspo
Areas with naturally occurring strong currents can retard normal
clams grow thick, bulky shells to protect the flesh.
Strong water movement is caused either by naturally occurring c
wave action can destroy cages, chip clam shells and overturn cla
downward instead of upward. Water movement due to cyclones (
similar damage. Further mortality can be caused by sand shifts,
clams or bury them alive.
Quiet water with good circulation. Clams thrive in areas with
Good circulation prevents the column of water from stagnating w
water with nutrients for the clams.
Giant clams have a narrow range of tolerance to changes in salin
established in areas away from freshwater runoff. Heavy rainf
high sediment load with river waters reducing light penetration in
Clear water with high salinity (not brackish). Giant clams re
penetration. This is necessary because they have symbiotic alga
in their mantles which are responsible for providing food for the c
At Orpheus Island Research Station (OIRS), Australia, where tidal
from James Cook University (JCU), North Queensland, found th
0.4 m to 0 .6 m gave the best growth rates and survival for T.giga
tides was about 3 hours at this tidal height.
CLAMS
found nea r the mouth of bays are also good areas for ocean
astro pods. In additio n, unless a damaged portion of a reef is
verely limit the size of the ocean nurse ry.
.
an ocean nursery can be established. Although the substrate on
and silt, there are some seagrass beds that have a firm, sandy
d fring ing the coastline away fro m bays and composed of several
ty Marine Laboratory, (SUML) Dumaguete, and at University of
te (UPMSI), Bolinao, the giant clams a re successfully cultured on
exhibiting good growth and survival rates.
n nursery
rs for Intertidal ocean nursery culture
el mesh unit, covered with plastic mesh or chicken wire. In the
ces of steel mesh (lOO mm aperture) were used : a rectangular
e lid and a larger piece measuring 2.3 m x 1.3 m for the base.
ded up along each edge to give the box its depth . The corners
ical cable or cable ties. Cable ties designed for outdoor
ny steel in them to prevent corrosion are used . A plastic mesh is
using the cable ties. The size of the plastic mesh used depends
5 mm aperture appears to work well. A hinge is made from three
ubing approximately 20 mm in diameter. The top wire of the
HINGE
SUBSTRATE
o 9m
111111~ Jo"
L
Box for intertidal ocean nursery culture
""\ "
~~
Figure 2.3
Figure 2.4
Line for intertidal ocean nursery
A line is the extension of the box which uses only the plastic mes
structure is derived from the use of galvanised fencing wire which
the pickets (Figure 2.4). Plastic mesh of 12 mm aperture is used
the lid. These are commercially available in 30 m lengths in Aust
line. Initially, the base is rolled out in the required position. The e
required 0.2 m. The corners are again fixed together using electri
raised a picket can be placed alongside the corners at one end. T
substrate until they are level with the top of the side. Working alo
driven into the substrate every five metres, carefully keeping the
end pickets. The galvanised fencing wire is threaded through the
second strand is threaded through at the bottom of the side to ac
case one breaks. One end is tied off around the end picket and t
helps to have an anchoring picket driven in at 45° and about a m
prevent the end pickets from being pulled out. Electrolysis occur
and the picket. To prevent this, a sleeve cut from reinforced gard
point. There are two methods of securing the sleeve: (1) by tying
Lines
Once the box is positioned on the reef-flat or on blocks in sandy
fencing pickets and electric cable. A substrate such as coral rubb
clams to attach themselves to. This substrate should be shovelle
Similar boxes could be made with a wood frame and chicken wir
tends to corrode in the intertidal zone.
framework is split at the centre of three divisions along one of the
the lid at the equivalent points. These allow the tubing to be slipp
base, thereby joining them. It is often necessary to make a short
beyond the split in the wire which can then be taped up. The lid is
electric cable.
CLAMS
y drilling holes at the correct height through the pickets with
re secure.
ivide the line into 15 cells. These partitions are made about
base and 100 mm taller than the height. The excess is used to
ste ning. The cell is 2 m long so 14 dividers will be used per line.
or tying them to the base. When this is done the substrate is
the whole bottom to a depth of about 50 mm. The line is now
ut along the full length, making sure that it is long enough and
d the windward side is secured with cable ties to the galvanised
pening edge is secured using electrical cable, two or three
id tied down securely. For every second cell a split is cut into the
proximately two thirds across the top. This allows the top to be
divider beneath a cut will need a 100 m piece laid flat along the
a pe from occurring at the cut. The split is joined using a piece of
artition.
ic mesh is to pull everything tight. It should not be put under too
movement during wave action and it is less likely to tear.
n nursery
w tide) site should be sought for subtidal culture. Clams are
a combination of these either on or without substrates.
Figure 2.5
Bamboo slot cage
I
- --'---
30em
-I
Cages
A bamboo base, bamboo strips and Leucaena trunks can be use
for covering. The net should be doubled on the bottom part of th
Net and bamboo or leucaena cage
Bamboo slats, such as those used in making the traditional fish t
(Figure 2.5).
Bamboo slat cage
Below are suggested types of benthic cages and their specific req
Experience at SUML, UPMSI and at Micronesian Mariculture Devel
nurseries has shown that cages have to be regularly cleaned of fou
shade the clams and overly restrict water movements. This can be
cages or replacing and drying them. In intertidal nurseries the cag
tides, cutting down algal growth and invertebrate colonisation. Th
is not recommended as the paint peels off too easily to be effectiv
Materials for clam cages depend on the raw materials locally avai
polyethylene, nylon or nylon netting material), bamboo, Leucae
others. Cages should be designed and positioned with the least p
ensure durability. This could be done by lowering cage height (a
of the cage with least surface area to the direction of the oncomi
behind big coral heads, firmly pegging the cage to the bottom, or
Clam cages function (1) to protect clams from bottom dwelling p
carnivorous fishes (e.g. triggerfish) and (2) to retard strong water
disturbance to the clams.
2.3.1
CLAMS
discourage the entrance of the bottom dwelling predators. The
with a net of larger mesh (25-40 mm mesh) to allow water
can replace Leucaena or bamboo as frames for clam cages.
amboo but are more durable. The size of the cage depends on
s type of cage are shown in Figure 2.6.
made from polyethylene like the ones employed at SUML and
hylene meshes are available in the Philippines at various mesh
h (approximately 20 mm) and 1/2 inch (approximately 12 mm)
vers, respectively. A 1.5 m length is cut from each roll and a
smaller mesh and a 1.2 x 0.6 m lid from the bigger mesh. Each
h an electrical cable wire to form a rectangle. Bottom and lids are
of the box. The cages are pegged to the bottom using iron bars,
k. Iron bars are fitted into the cage fold of the bottom mesh. Two
strate keep the cage at the bottom.
Bolinao uses polyvinylchloride (PVC) pipes as frames (Figure
ce they are more durable than bamboo frames . The case and the
esh size as at SUMl.
d when deploying clams with shell lengths less than 60 mm.
orated trays. The bigger mesh (20 mm) is used for clams larger
ced directly on the cage. The cage is elevated one metre from the
bars to minimise predation from benthic organisms. 'Skirts'
ed on each post to prevent predation from herm it crabs and other
on the clams (Figure 2.8).
Figure 2.6
A
Figure 2.7
IRONBAR ~
20m
,-
Cage made of net and iron bars
----. j
A. Plastic cage design utilised at SUMl.
B. Plastic cage design utilised at UPMSI
Figure 2.9
.--J
/ 1
...
Figure 2.8
/
/'
-~~ l
2 '
PVC-coated wire mesh cage
----------
~
/
'1!.~')
.
Platform design used by UPMSI
':/
Platforms
Enclosures
Enclosures, fences or pens (Figure 2.11) can be used as protectio
ocean nursery area has most of the requirements mentioned for si
2.3.3
In shifting sandy-seagrass areas as in Bolinao, Pangasinan, Philip
become buried by mounds of sand produced by burrowing organ
elevated 200-300 mm from the bottom (Figure 2.8) are used . Th
materials as the PVC cages.
2.3.2
Advantages over other materials include ease of handling during
to wire diameter (which means that less surface area is available
between the mesh and cement used for the cage base. The main
is the susceptibility of the wire mesh to corrosion, which limits th
depending on wire diameter and cage location.
In many countries the cheapest and most easily available cage m
mentioned above, are a variety of galvanised wire meshes such a
wire mesh products. Galvanised wire meshes are used extensivel
ICLARM-CAC, in benthic and floating cages (Figure 2.10) and al
Galvanised wire cages
PVC-coated galvanised wire mesh (14 gauge) is widely used by
are made into either square or rectangular cages with two remov
Figure 2.9 shows an example of a cage made with wire mesh .
PVC-coated wire cages
CLAMS
ges
nclosure held in place by bamboo or wooden (Leucaena) posts.
rowout phase except for the presence of the net enclosures.
mesh fence anchored to the substrate and floated from the
htly different from an enclosure, which does not have floats . The
ean nursery needs to be determined prior to construction so that
but not sink the floats. Once the height above the substrate has
eds to be added to use as the skirt around the bottom.
ion is best done on land. The netting is prepared in two sections,
plus some overlap). The oyster mesh comes in 2 m wide rolls. If
Figure 2.11
Clam enclosure
-
r1-
I
ISm square
0)
v
V-
v
lA
,
~
_
~o. 'm'
j\
G
~
,">
~
~ w" h flo015
pe
During a good low tide, the area for the excIosure should be mar
To prepare the float line, a 250 mm ball float with a central hole i
balls along each side. Each float is separated by a plastic sleeve
The length of each piece of tubing is the same, the two end ones
the extra diameter of the end float). Each 15 m side can be made
attachment to the net.
two widths must be joined this can be done using 3 mm rope wo
mesh should lie flat along the full length, with the ends securely ti
threaded along the top edge. One rope is positioned close to the
below it. These are used to attach the float line to the net.
A. Exclosure for subtidal ocean nursery - JCU design . B. Exclosure for subtidal ocean nursery utilised at UPMSI.
/'
~~
Figure 2.12
I~
I!
-
.v
~
.f,
MarKer ouoys ------.J
CLAMS
er two sides are measured, making sure that a true square is
with two more pickets per side installed 5 m apart. The netting is
nised fencing wire threaded through the mesh and leaving the
closure. Precautionary measures should be taken against the
2.2.1 on lines). After one length is attached it should extend
st beyond the opposite corner. The other 31 m length can also
p occurs. This means that there is an overlap of approximately
can now be joined using 3 mm rope threaded through alternate
at against each other and the top edges are lined up. If two
by a small gap, it makes the joint more secure.
ched. Starting at one corner, the top of the net is wrapped over
s are attached together using cable ties. Three ties per length of
are should be taken not to put a tie too close to the float as it will
t is important to make sure that all along the float line the tubes
ners, the loose ends of the rope from each side are passed
d tied together outside the float. This acts as a joining point for
in place, the loose ends of the rope are trimmed and sealed. The
and tied to a picket placed diagonally off the corner. The guy
g the corner down at the highest tide. If 3 mm rope is tied at
grid pattern inside the exclosure the clams can be monitored
t.
along it to prevent any benthic predators from crawling under it.
he ends are tied off, the ties are all tight and that there are no
ed together.
uring low tide, the net slackens and covers the clam at the
cation of this design is employed in Bolinao (UPMSI) where
height of the low tide level (see Figure 2.12B). With this design ,
ater mark is still upright even during low tides.
I
t===i':.';-=
/
1/
/
/' /
I
/
/
/
/
I
/
/
I
I
/
I
I
/
/
I
,
I
/
I
/
_
/
I
, T.
/-~ ~ ---(
embedded stones
A. Concrete block; B. Block with
/
I 1/ /
/
I
I
/ /
I
/ I
/
_ _ _ 0 5m _
B
Gravel
Concrete blocks
Concrete blocks (Figure 3.1) offer juvenile clams substrates with
Block size depends on the size of cages - a rule of thumb is eas
3.2.2
Gravel 20-30 mm in diameter can be used for substrate. It is po
cells to a depth of 50 mm.
3.2.1
Large pieces of coral rubble and stones may be placed between
water movements to prevent them from being washed about.
Juvenile clams are allowed to attach to substrates in the land nu
nursery. The attachment of clams can also be delayed until plac
nursery. However, transfer should only be attempted during cal
daily for possible displacement until attachment is strong enoug
In the ocean nursery , substrates are used for the attachment of t
clams from being moved by water currents. Substrates for byssa
coral, limestone, coral rubble, stones and cement.
All clams possess byssal threads for attachment during their earl
these are retained in some species (T. squamosa, T. maxima , T
The other clam species mainly rely on their shell weight to hold t
3.1 Substrates
Olean nursery ,ulture 01 Ilams
3
~
Figure 3.1
A
Chapter
LAMS
m x 3 cm supported by a wire mesh frame embedded in the
s scratched with 50 1-mm lines, using a common nail to create
wise smooth surface. Juvenile T. crocea and T. maxima were
in the land-based nursery before transfer to the ocean nursery.
pecies cultured at the laboratory. One modification was making
Another modification was embedding gravel (20-30 mm) in
ore surface area for clam attachment. The embedded gravel
clams with weak byssal attachment. Smaller sizes (5-10 mm) of
over the entire surface of the block. Smaller areas for
appear to attach more readily.
ks per 1 m x 0.5 m cage used by SUML. Smaller blocks,
ater and fit into cages.
constructed of wire-reinforced concrete. A frame for the base is
r galvanised material such as angle bar. Galvanised chicken wire
oss the frame and covered with a thin layer of concrete (about
considerable reduction in weight compared to other concrete
ade. These bases are commonly used in floating systems at the
sed at CAC are 1.5 m x 0.75 m and 1.0 m x 0.75 m. In the case
h folded into the shape of a basket or box, the base of the cage
ge size does not exceed 1.0 m x 0.75 m.
bers of iuvenile clams
nursery tanks by cutting the byssal attachments with a sharp
ut cleanly and the clam should not be pulled. The clams are then
Stockl ........ 'Ity
For a cage size of 1 m in length x 0.5 m in width x 0.3 m in heig
(30-50 mm) can be stocked. For bigger juveniles (70-80 mm),
For an intertidal box or cell (of a line), stocking density of about
recommended. Keeping the density reasonably high helps to con
chains must be monitored closely for the possibility of overcrowd
substrate is covered by clams then they must be thinned out bec
inhibited. When the clams are about two years old then 30-45 p
a cell. It is important that if the clams have a seasonal growth pa
summer to allow them to have uninhibited growth during their fa
3.3.1
3.3 Stocking with juvenile clams
Measure clams by starting with a known volume of seawater in a
add clams to 198.5 mL.
51 x 3.5 = 178.5 mL.
Therefore, for 3500 clams:
Le. 51 mL = 1000 clams
5.1 mL seawater displaced per 100 clams added (average of 1
For example, for 3500 clams per ocean nursery container:
siphoned out of the tank into an appropriate sized screen and the
clams each, randomly counted, are made. A pile is added to a gr
of seawater and the increase in the volume of water is recorded.
is calculated.
OCEAN
CLAMS
mensions. Once the clams start to appear crowded, they should
ld be transferred to another cage).
grid can easily take 90 two year-old clams. Up to 120 can be put
to be thinned at a later date. It they are left in the exclosure until
directly into the growth areas. The alternative is to remove the
n and setting up the exclosure somewhere else.
g juveniles are listed in Box 3.1.
rs of travel juveniles must be wrapped in moist cheesecloth or
d boxes to prevent desiccation and jarring of clams. If transport
oist cloth need to be placed in plastic bags to which pure
can be procured from oxy-acetylene outlets.
d be set up before the arrival of the juvenile clams. If clams are
ld be lowered into the sea water to allow the clams to adjust to
re then unwrapped and sprinkled with sea water. When
red to the nursery tanks.
of juveniles
rowth and survival of batches of juvenile clams at least 3-4
nal differences and the general growth rate to be expected in
ed is basic: a vernier caliper (200+ mm length) , made of good
T. deraso
T.cr«eo
Spedes
AuslrmlO: Reeform 01 Cairns
Morsholllslands: CIomform 01 Wo'u I.
Solomon Islands: CA( 01 Honiaro
Poluo: MMDC 01 Koror
Philippines: SUML 01 Dumoguele
Austrolia: Reefarm HoIcheries 01 Coims
Polou: MMDC 01 Karor
Philippines: SUML 01 Dumoguele
UPMS 01 Bolinoo
Location
Sources of juvenile giont cwms
T. gigos
A~: 01 Mokogoi
Phitlppines: SUML 01 Dumoguel'
BOl3.1
T.moximo
H. hippopus
T. squamaso
Polou: MMDC 01 Koror
Philippines: SUML 01 Dumoguele
Austrolio: Reeform 01 Cairns
Polou: MMDC 01 Koror
Philippines: SUML 01 Dumoguel,
Solomon I.: UC 01 Honiaro
Aji: AJ Mokogoi
Philippines: SUML 01 Durnoguele
Tongo
H. parcel/onus
If a stocktake (keeping a record of the total stock by counting a
is carried out every six months then an accurate account of the
After the ocean nursery has been operating for a while it will be n
different areas to allow for their increase in size. If accurate recor
confused. It pays to establish a program so that age classes are
important to keep separate spawnings distinct, then it is vital to
placed.
Records of clam seed, including age, mean size, spawning date a
This information is usually indicated in the receipt given by the h
3.6 Records
When weighing clams, the animal should be inverted on a paper
weights are taken. If the clams are sensitive to drying (especially
easiest and probably most accurate method is to weigh the clam
the clam and then get the weight of just the mantle cavity water.
difference between total weight and weight of water.
A randomly chosen group of 50-100 juveniles which are about 4
individually tagged with plastic Dymotag numbers and two-part e
Aquatopoxy) onto a cleaned and dried area of their shell. These t
the nursery and regularly measured. Individual tagging is superio
at each measurement because individual growth increment incre
individuals are measured each time.
plastic or stainless steel for shell length measurement and a bala
2-3 kg. A measuring board can also be constructed such as is u
lengths.
OCEAN
CLAMS
es the farmer to determine if there have been any major losses
ng general monitoring. Also total average weights can be
r the total farm for determining production rates.
sery include the following:
off algae and other organisms growing inside and outside the
ry few days to prevent dense algal growth which will be harder to
on on predator control in Chapter 5);
mination of the shells for probable causes of death;
ges when they become overcrowded;
age and destruction of anchors;
, strong wave action,and other occurrences which may affect the
d
,
Growout phase
4
Figure 4.1
Clams during the grow out phase
o£Jo~,~~
~~@V£< '~~Q
~
..
..r"O~
~1~-6 ~ ~
~ ~
_A-~~d..
'
<:if--;:::C --.-- . eT ~ ~~Jf~~ ~)
Chapter
no data
no data
3
3
2.5
2
3
T. g;gas
T. derasa
T. squamosa
H. h;ppopus
H. porcel/anus
T. maxima
T. crocea
Age (year)
180
150
150
150
220
Size (mm)
Age and size of transfer of diFFerent species of giant
Species
Table 4.1
Once the juveniles reach a certain size (about 200 mm) or age
withstand predator attacks and environmental stresses they are
culture. The protective mesh containers or the enclosures in whi
away and these more mature juveniles can be left to grow out to
4.1). Table 4.1 summarises the data gathered from several place
transfer clams to growout area.
4.1 Transfer to growout site
CLAMS
or growout
cean nurseries. The sites may either be adjacent to the ocean
y from the nursery.
niles
hose from the ocean nursery which have reached 'escape size'
y also be purchased from agencies with ocean nurseries and
ral ways. One way is by placing the collected animals on their
haded area of the transporting vessel. The clams must be
e to time. Clams can also be transported by putting them in
d aerated. If possible, a wedge (Le., tyres or wood) must be
pport it and prevent excessive jarring during transportation.
clams should be wrapped in moist cloth and placed in insulated
urs, the wrapped clams are placed in plastic bags and pure
f clams in growout area
grouped together and separated from other species. They
so that the valves will not touch. Each clam should be able to
another clam.
Growout sites should be visited as often as possible, preferably e
clams that have changed position, been preyed upon, or have ot
may indicate the occurrence of a disease, parasites, predators, h
environmental conditions.
4.6 Monitoring
Chapter
Ranellidae (= Cymatiidae)
The species most commonly found attacking juvenile clams is C
Perron et al. (1985) but C. aqua tile, C. pileare and C. nicobaric
attack in the same way. All four species are shown in Figure 5.1.
been observed consuming clams and may prey in the same way
and Belda 1988). Juvenile Cymatium sp. are frequently found in
Members of this sea snail family (which until recently was known
carnivores found throughout the tropics. They occur at almost all
Pacific. Ranellids cause mass mortalities of ocean nursery clams
biological constraint to the ocean nursery culture of giant clams.
5.1.1
During the ocean nursery phase, juvenile clams are protected by
voracious predators. Nevertheless, there are some predators that
mesh and can kill many clams. These are listed in Table 5.1. The
just a few groups and these, together with methods for their contr
sections.
Most mortality of juvenile clams in a well-sited ocean nursery will
pests. The success of the whole clam farming operation may well
adequate control of these predators.
5. 1 Predators and pests
Predators and predator (ontrol
5
CLAMS
o prey on giant clams
Species
Sty/ochus sp.
Cantharus fumosus
Vexillum plicarium, V. cruentafum?
Cymatium aqua tile, C. muricinum, C. nicobaricum, C. pileare, C. vespaceum?
Pleuroploca trapezium
Chicoreus brunneus, C. microphyllum, C. ramosus, Cronia fiscella, C. margariticola, C. ochrostoma, Morula granulata,
Thais aculeata
Tathrella iredalei, Turbonilla sp.
Melo sp.
Octopus spp.
Dardanus deform is, D. lagopodes, D. pedunculafus.
Gonodacty/us sp.
Thalamita spp.
Afergatis spp., Carpilius convexus, C. maculafus, Demania alcalai, Leptodius sanguineus, Lophozozymus pictor,
Zosimus aeneus.
Balistapus undulafus, Balistoides sp., Pseudobolistes sp., Rhinecanthus sp.
Monotaxis grandoculis
Choerodon spp., Cheilinus sp., Halichoeres sp.
Canthigasfer valentini, Tetradon sfellafus.
Aetobatis narinari.
Figure S.l
,
Growth series of the fou r species of
Ranellidae most commonly found preying
on juvenile tridacnid Clams. From top to
bottom : Cymatium muricinum,
C. aquatile, C. nicobaricum, C. pileare.
Note the different protoconchs,
particularly in juvenile shells.
Muricldae
Muricids slightly resemble some members of the Ranellidae, but
more abundant ribs and their lack of any hairy covering. Some m
(Muricodrupa) fiscella and Chicoreus brunneus drill holes thro
through which they feed, while others such as Chicoreus ramosu
gaping valves of the clams. Small clams placed directly on the se
the substrate is coral rubble or rock.
Muricid seasnails are well-known pests of cultured bivalves in tem
abundant in coral and coral rubble substrates. A number of speci
juvenile giant clams but have rarely been reported to cause exten
5.1.2
Adult or sub adult Cymatium are voracious predators, usually att
consuming up to 10 juvenile T. gigas (30 mm shell length) per w
toxic saliva into the clam through the mantle or byssal orifice, qui
large juvenile clams (up to 200 mm). The dying clam is then rapi
free-swimming larvae which are capable of drifting in the ocean f
kilometres. When a suitable substrate is found the larval snails se
giant clams provide such a substrate, inducing settlement. Certai
just a few millimetres within, or close to, juvenile clams in ocean
clams at this virtually undetectable size and proceed to feed, som
internal surfaces of the clam's shell. Eventually the juvenile clam
which time the snail has grown to a visible size (6-20 mm) . The s
nearby clams. Because these snails often attack at night and are
when very small, they are often not identified as the cause of mor
usually distinguished by their thin shells, prominent protoconch (
juvenile shell) and by their sometimes dense covering of fine hair
PREDAT
CLAMS
many species of cultured bivalves, including giant clams
ported to affect giant clams; Turbonilla, which has been found in
s and Fiji, and Tathrella, which has been reported from Palau to
han 8 mm) and appear white and fragile (Figure 5.3) .
izes of clams, juvenile clams are more seriously affected.
snails and the size of the juvenile clam, effects range from loss
th of the juvenile clam. Usually mortality only occurs after a
may cause the clam to form blisters on the inner surface of the
ear the byssal orifice. Shell thickening and uneven growth
ay also be present. The mantles of affected clams may be
-like scars.
valves of clams, under the clams or on the nearby substrata.
e or other refuges during the day and come out to feed at night.
xible snouts to suck the clams' body fluids , either from the edge
ifice.
3-4 months, and once a breeding popUlation is established, they
l orders of magnitude over just a few months.
s are known to be serious pests of cultured oysters and mussels
pecies of flatworm belonging to the family Stylochidae has been
ocean nurseries for T. gigas at Solomon Islands (Figure 5.4) .
ve an irregular shape. Their light-brown to grey colour makes
d in well with clam shells and the cage substrate. They vary in
in length. Nothing is known about the distribution of the species
Figure S.2
Some species of Muricidae and
scavenging organisms commonly found
in ocean-nurseries. Clockwise from top
left: Chicoreus brunneus, Cronia
(Muricodrupa) fiscella, Pyrene turturina
and Cronia ochrostoma.
Figure 5.3
Pyramidellid parasites (Turbonil/o sp.) on
a juvenile Tridocno gig05. Photograph
courtesy of John lucas.
Boring sponges
Other predators
A variety of other animals can prey on clams (Table 5.1). Specie
Portunidae), hermit crabs (Dardanus spp.) and fish (such as trig
5.1.6
These sponges are visible on the outer surfaces of the clam's shel
obvious on the underside of the clam. The holes vary from 0.5-1.
sponge tissue which may be orange, yellow, green or brown (Tho
the clam's shell the boring sponge appears as a network of chan
sponge and in seriously infested clams the shell may be blistered
particularly boring algae and bristle worms may cause similar da
same way as boring sponges (Velayudhan 1983).
Some kinds of sponge have been found to bore into the shells of
can make clams so weak that they either die or are easily killed b
sponges are usually only a problem in older clams which are rais
resistant to most other pests and predators and therefore not so c
farmer.
5.1.5
Although flatworms are not particularly voracious, they reproduce
reaching high densities in clam cages. They then infect nearby ca
flatworms are usually associated with increased mortalities of juv
have been found only in cages raised off the seabed.
found in Solomon Islands but similar species can be expected thr
how the stylochid flatworm kills clams, but the flatworm enters th
orifice or the inhalant siphon, the clam soon dies and appears to
lay their egg masses on the inner surface of the dead shells of cla
settle on the cage.
PREDA TO
CLAMS
ells. Clams are usually protected from these animals by cages or
an sometimes find their way into cages through badly closed
, as do stone crabs (Figure 5.5) and triggerfish.
clams open to eat them. Often empty clam shells from an
stance from the cages. Octopuses are able to get into even well
sented a major threat to clam farms.
ol
predation on giant clams is regular and thorough checks of the
rence tends to be sporadic or occasional, it is important that the
though no problems have been detected for a considerable
ied out two or three times a week but greater frequency may be
or a mass mortality of clams has occurred. When clam mortality
onmental conditions or poor maintenance, dead or dying clams
ties. When such clams are found during routine checks, the
as well as the empty shells, the cages and the immediate
uld be paid to apparently inoffensive, small (3-5 mm) snails.
muricids, may be identified from characteristic markings made
predator's feeding behaviour (Table 5.2). Dying clams should be
edators or may contain pests that will affect other clams.
Dead shells, debris, fouling animals and algae should be removed
suitable egg-laying substrates for predators. In this respect, the
e important as gravel and coral rubble may provide such refuge
h substrate will not, thereby making predator detection easier.
rom cages except for known grazers such as top shells
Figure 5.5
Figure 5.4
Carpi/ius convexus, a xanthid crab
capable of preying on juvenile
tridacnids.
Turbellarian Ratworms (Sty/ochus sp.)
from Rooting ocean-nurseries in Solomon
Islands.
possible causes
Crabs, hermit
crabs, fish
Muricid snails
Pyramidellids
Juvenile ranellids
Pyramidellids
Octopus
Chipping or crushing
Drilled hole/ s
Blistering on internal
surfaces
Layering or thickening
along valve edge
Ligament torn and/or
hinge dislocated
possible causes of predatorrelated shell damage in juvenile
Tridacna 9i9as.
Shell damage
Table 5.2
Control of Ran.llida.
Control of pyramid.md,
Control of flatworm.
Infestation can largely be prevented by keeping cages clean and
5.2.4
Minor infestations can sometimes be controlled by manually rem
serious infestations, all the clams from the affected cages should
The cage and substrate should be soaked in bleach and rinsed or
where such infestations pose a continuous threat, it may be benef
basis (e.g. every three months) in order to prevent infestations re
be considered (see Section 5.3).
5.2.3
If a problem is experienced with adult snails entering cages from t
help to raise the cages above the substrate, using trestles, posts o
Regular thorough checks of the cages are essential for the control
inspections should be made when infestations of juvenile snails ar
due to juvenile ranellids settling in clam cages may become unac
efforts at control by the clam farmer. In such cases it may be nec
a new depth or in a different position with respect to the prevailin
be necessary to relocate the whole clam farm.
5.2.2
These gUidelines should be generally applied to control most pred
a particular predator, then more specific action is required as outl
(Trochus spp.) turban shells, and cerithiid gastropods. This is bec
cages, although not capable of killing clams, may be scavengers
(see Section 5.3 on biological control).
PREDA TO
CLAMS
d suitable egg-laying substrates. If necessary, clams from affected
d and the cages sun-dried. This action can be repeated every 3
cted. Serious infestations may be controlled by removing the
efly spraying the contents with fresh water. This only kills the
not appear affected by the brief exposure to fresh water.
es
te from healthy clams to prevent the infestation from spreading.
g the outer surface of the shell with formalin. The affected areas
solution and left out of the water for about one hour after which
water before placing back in the sea. Caution: great care should
e in contact with the clam's tissues.
ators
dators may be slowed down or stopped by a variety of methods.
or octopus. The use of tangle nets near the cages may control
an be used to control some fish and hermit crabs. However, most
d from clam cages by the use of suitable mesh sizes or by raising
or trestles. Inverted plastiC cones (Figure 2.8) can be placed on
rom climbing into the cages.
rol of predators
, hermit crab and fish (portunids, palinurids, diogenids and
at pyramidellids and can be expected to consume juvenile
pecies, if large enough, are also known to eat juvenile clams.
ed or the size of the control agents is rigorously screened there
ogical control.
Figure 5.6
Fish trap used at UPMSI to remove some
predators.
The species of giant clam being cultured may also affect the level
the ocean nursery. Some clam species may be more resistant to
resistance at an earlier age or smaller size. For instance, Hippopu
resistant to ranellid and some other predators than Tridacna giga
It has been noted that densities of pyramidellids, juvenile ranellids
in the case of f1atworms, nonexistent in benthic cages. This may b
organisms feeding on these predators. This suggests that mesh si
enough to allow access to such organisms while excluding clam p
PREDATO
Chapter
In Australia and the the Pacific, winter mortality may cause heavy
where the temperature drops below 20°C. The epithelium of the
T. maxima may contain banana-shaped, intracellular bacteria of
chilling produces retraction of the mantle followed by secondary
protozoa, and finally death.
The protozoan parasite Perk ins us sp., has been seen in both juve
like protozoan parasite has also been seen in an adult clam. A lar
(Bucephalidae) has been found infesting the gonad of adult T. cr
been discussed in Section 5.1.
Bacterial disease may be a problem in larval and juvenile stages.
contaminated culture facilities, algae contaminated with bacteria,
levels in the water and dead clams in the tank. Bacterial disease
secondary to environmental or managerial stress. Rickettsia, an
clams of all ages but infections may be most heavy in juvenile cl
6.1 Summary of diseases reported
While there is a large body of literature on diseases of molluscs, t
diseases, pathogens and parasites of giant clams. This is probabl
cultivation of the giant clams compared to other molluscs. Excep
chlamydia, mycoplasma, fungus or neoplasm has been reported
the deaths in cultured juvenile and adult giant clams have been a
environmental factors rather than specific infectious pathogens.
Diseases and parasites 01 giant "ams
6
CLAMS
ms kept in small, land-based aquaria or tanks. Prolonged
at and cold stress along with insufficient sunlight have been
mantle in clams, wherein part or all of the siphonal mantle will
y be associated with a defiCiency of nitrogen.
as bubble disease may sometimes cause losses. Air bubbles will
mall clams may float to the surface. Allowing for temperature and
on of pumped water prior to use will solve this problem.
arts per thousand, will cause the clam to close its shell valves
y may be associated with swelling of the edges of the siphonal
he above infectious agents and parasites are at present unknown.
e or other as yet undiscovered infectious agents, the movement
ms, regions or countries involves a risk of also moving infectious
d juvenile clams for translocation between centres therefore need
A quarantine protocol to ensure that the latter is carried out is
specimens for histology
, which holds the clam's shell valves closed, must be cut. This may
he clam, or (2) placing a strong wedge, e.g., of wood, between the
ong, thin knife or scalpel is slid along the inside surface of the shell
/pedal retractor muscles where they attach to the shell. Once this is
will be relaxed. The attachment of the siphonal retractor muscles to
Fixation
The purpose of this protocol (Box 6 .1) is to allow larvae or juveni
6.3 Quarantine protocol for impor
After the tissues have been in the fixative for 2-3 days, they may
cloth dampened with fixative , and placed in double, strong plasti
tape. The tissues may then be placed in a strong container (e.g .,
and mailed or sent by courier to a laboratory for histological proc
in handling formalin. Avoid inhaling the fumes or contact with th
The procedure is as follows : cut sections of each organ or tissue,
new scalpel or razor blade. This thickness is important as this is g
which the fixative will penetrate before the cells deep in the tissue
as important and a piece of tissue approximately 10 x 10 mm is
clams 4 months of age or over, place the sections in 10% seawat
100 mL 40% w/v formaldehyde solution and adding to 900 mL fi
container for ease of removal when fixed, ensuring that there is 1
each volume of tissue. Tissues from clams under four months of
seawater/formalin as the 10% seawater/ formalin will dissolve the
6.2.2
The above procedure may be repeated for the remaining shell val
clam are removed as a unit. The organs of the clams may be dis
lateral mantle, the siphonal mantle, the gills (ctenidia) and labial
kidneys, the reproductive organ, the digestive organs, the byssal
muscle.
the shell valves along the pallial line can then be cut free so that the
hinge ligament is cut or broken by bending the shell valve back an
PREDAT
CLAMS
rting giant clams.
ven~esl to redlKe the risk of a carrier status.
or eadt batch of dams inportecl.ldentily all these fO(~ities as
uthorised staR only.
ected, rinsed and dried prior to use. This is done by subjecting
Um hydroxide solution (lOg NaOH in 1litre water I using a brush
num temperature of 60 qc. This is followed by soaking for 1 hr
orinel or sod'lUm hypochlorite solution (sullicient amount is
n of at least 10 mg/t remains aher 30 minI. Aher soaking, the
hwatw and allowed to dry.
exduded from the quarantine area.
er and fed with Iaboratory-cuhured algae or artificial diets. If this
ed to alow the entry of phytoplankton. However, this aka aUows
nsussp. which ore 4-5l.1li in sizel and may confuse the issue as
e quaranHned dams.
140
145
150
Sample size
10. Rondom samples should be collected for laboratory examination at 6weeks and 12 weeks aher the time of arrival of
the clams into the importing country or agency. The minimum sam~e size to detect a 2% prevalence of ea<h infection
(with 95% confidence I, assuming that the test is 100" reliable, is as folows:
Batch size
1000
10000
100 000 or more
Each sampling should include gross examination, Pericinsus sp. cuhure and histopathology (preserved in buffered
3-5" seawater formalinl.
11. An stress should be minimised to redlKe sickness or death which may mask the presence of 0 pothogen or porasite.
12. Aseporate set of equipment must be used for each tank/pond (e.g., brushes, nets, etc.l. Staff should disinfect their
legs and feet with 60 mg/L free chlorine solution before entry into rearing ponds/tanks.
•
•
Any RicJcellsio or (hhrrryJio
Any bacteria, protozoan, metazoan parasite or fungus associated with on inHammatory or degenerative lesion or
known to be a pathogen for other marine animab
Any lesions, e.g. inclusion bodies, or focal necrosis which may indicate the presence of a virus
Clams are deemed unsuitable for release into the local marine environment ond should be destroyed If
the following are found:
e disposed of into 0 land-based sump (e.g., sand trench I to
athogen or noxious agent that may be present in the imported
•
Any unexplained lesion
owing the protocol in No. 3. Deteriorating filters must be
hould include the foNowing details: cleaning, nutrient
•
Any unexplained mortality.
~ty, /ilter changes, water exchange rates, water temperature
•
m of 3 months.
from one region to another with minimal risk of introducing pathogens or noxious agents. Quarantine
protocols must be practiced both by the importing country or agency as well as the exporting country
or agency. The protocol given in Box 6.1 is that which should be followed by the importing country or
agency. For information about the exporting country or agency see Braley (1992) .
PREDAT
Meal
The main potential market for giant clams is for their meat (whol
mantle) but much must be done to develop this market in more
re-establish it where it has 'withered' due to insufficient supply of
developed countries, the main current market for giant clam mea
extent, T. maxima in the southern islands of Japan. Currently, it
meat from other species of giant clams to be a poor to unsatisfac
species. No market for giant clam meat has yet been established
Currently, only small remnant markets seem to exist for giant cla
and then only for the adductor muscle, especially that of T. gigas
7.1.1
The main end-markets which have been identified for giant clams
aquarium.
7.1 Markets
Giant clam farming is not yet a well-established industry but a fe
the commercial production and culture of giant clams. Because t
development, there has been little time for commercial data to ac
techniques are still in the development stage and firms entering t
for learning by experimentation and by experience. Success in th
heavily on entrepreneurship, especially in the establishment of m
industry at present should be regarded as venture capital. Nevert
techniques have been established and profitable possibilities exist
Economics and marlce,s
CLAMS
New Zealand and Australia among Pacific Islander immigrants.
to the tourists. The number of Japanese tourists to Australia is
e mainlanders do not usually know of giant clam dishes, they do
yukyu Islands. A substantial ethnic market for giant clam meat
y California and to some extent Hawaii because a large number
e migrated there. In Hawaii, the tourist trade represents a
s in Quam.
l established despite restrictions on international trade in giant
e Convention on International Trade in Endangered Species).
T. gigas and Hippopus porcellanus), are now in very short
opus seem to be most in demand with T. squamosa also of
rade (Juinio et al. 1987). It should be noted that some species
their meat, e.g., T. crocea has little value for its shell. A
der such factors in deciding which species to farm.
ms in developed countries as saltwater aquarium specimens.
d to the market by MMDC (Palau) and Reefarm at Cairns
ket is limited, it represents a worthwhile sideline outlet for a giant
g market which can be expected to improve in operations as
ore regularly available and can be better adapted to customer
or this trade are T. crocea and T. maxima because of their
nt clams as biological specimens for scientific demonstration
Economies of scope, apart from economies of scale in hatchery
in giant clam farming. This means that there may be economies
of activities, e.g., hatchery-nursery operations as well as ocean
boats have been purchased for hatchery-nursery, they may be u
operations if these occur near the hatchery-nursery. As a result,
be achieved. Furthermore, labour employed in hatchery-nursery
ocean nursery and growout operations, including surveillance w
operations are located near one another.
If the business is not already operating a hatchery-nursery, it wil
whether to purchase juveniles or to produce them itself. It will ha
juveniles with the cost of producing them. If only relatively small
on, it is most economic to purchase these rather than produce t
7.2 Whether to establish a hatche
Each of the end-markets may be subdivided into sub-markets. F
for meat for sushi, for the muscle, for the mantle and the whole
Species differ in their ability to satisfy these different markets an
deciding which species to breed and rear and whether to establis
a commercial ocean nursery and grow-out.
and experimentation purposes. It is possible that additional endthe clam for health or medicinal purposes. Particular attention sh
high value products from clams. For example, the inside of the s
be used for scrimshaw as was done by the ancient Babylonians.
scrimshaw can be seen in the British Museum.
LAMS
sions
e ocean or kept on land in suitable tanks, containers or ponds.
d may be limited by available space, pumping costs of seawater
container construction. The advantage of land-based nursery
ms from predators and diseases. If ocean nursery culture is only
are 2-3 years old, to satisfy aquarium, sashimi or sushi
2-3 is obtained for 2-3 year-old clams this method could be
ume of operations (500000 clams per year).
the ocean at about 10 months old, first of all keeping them
y reach escape size growing them out unprotected in the ocean.
ltivated, growout may be subtidal or intertidal. Each has its own
species specific. Choice of species to farm will be affected by
iderations.
e optimally held in the ocean until they are around five years old.
aximise the volume of meat production per unit. But in the initial
a cash flow problem. The time factor complicates the modelling
uction. The longer money is tied up in production the greater the
one. Economists allow for this by discounting, for example, by
y estimating internal rates of return on funds employed. This
example involving the ocean growout of T. gigas.
stralia (James Cook University-Orpheus Island Research
nt of the ocean culture enterprise independent of
nces were made for equipment such as utility truck, workers'
es and lines. The main operating costs were the cost of seed
ur.
The above example does not allow for possible additional revenue
sales of shell. Also it has been assumed that no transportation cos
farmer, or that these are not substantial for the farmer. In any case
clam meat in central food processing factories, e.g., freezing plant
done by farmers. This, for example, used to be the pattern in Fiji u
clam muscle was frozen and exported and the mantle was sold loc
outlets. The Fijian processor was also involved in preparing and m
Using these average prices, specific allowance can also be made
transit. It has been shown that up to 40% of the weight of clam m
al. 1991). This represents a substantial loss. But it is conceivable
could be developed. Nevertheless, after such weight loss, if giant
$12/kg retail, clam farming may still be economic. Assuming a 1
farm and retailing, such a loss would still result in $3.60/kg for th
In practice, adductor muscle and mantle of giant clams may be s
considered above should be regarded as average prices, taking i
muscle represents about 15% of the whole meat weight. For exa
$30/kg on the farm, this would account for a value on average o
price received on the farm for adductor muscle is as low as $20/
clam meat.
Internal rate of return analysis using the same data and assumin
the internal return on ocean culture of giant clams for meat to be
estimates allow for mortality rates for giant clams considered to
Assuming that 100000 clams were placed in the ocean annually,
maximise the firm's net present value, using a 10% rate of interes
considering prices of clam meat of $3-7/kg . Net present value i
culture even at on-farm price of as low as $3/kg clam meat. Fur
clam meat, a positive profit can be expected.
Parry, R., Saunders, T., and Munro, P.E. 1991 . Investigations into the p
from giant clams. ICLARM/ ODA NRI Report 40 p.
Lucas, J.S. , Ledon, E., and Braley, R.D. 1991. Tridacna tevoroa Lucas
species of giant clam (Bivalvia; Tridacnidae) from Fiji and Tonga .
Lucas, J.S. , Braley, R.D., Crawford, CM., and Nash , W.J .1988. Selecti
nursery culture for Tridacna gigas. In: Copland, J .W., and Lucas , J
Pacific. ACIAR Monograph No. 9,129-132.
Lucas, J . 1988. Giant clams: description, distribution and life history. In
Giant clams in Asia and the Pacific. AClAR Monograph No. 9, 21-3
Uttlewood, D.T.J . and Marsbe, L.A. 1990. Predation on cultivated oyste
(Guilding) , by the polyclad turbellarian flatworm, Stylochus (Stylo
145-150.
International Centre for Uving Aquatic Resources Management (South
Aquaculture Centre Annual Report, Jan 1990-Dec 1990
Juinio, A., Menez, L , and Villanoy, C 1987. Use of giant clam resource
Heslinga, G., Watson, Tu and Isumu, T. 1990. Giant clam farming. Paci
(NMFS/NOAA), Honolulu , Hawaii, 179 pp.
Gomez, E. and Belda, C. 1988. Growth of giant clams in Bolinao, Phili
J.S. , ed., Giant clams in Asia and the Pacific. AClAR Monograph N
Estacion, J . 1988. Ocean-nursery phase for giant clams in the Central
and Lucas, J .S., ed ., Giant clams in Asia and the Pacific. ACIAR Mo
Cumming, R. L 1988. Pyramidellid parasites in giant clam mariculture
J.S., ed., Giant clams in Asia and the Pacific. AClAR Monograph N
Crawford, C , Lucas, J. and Nash, W. 1988. Growth and survival during
clams, Tridacna gigas. I. Assessment of four culture methods. Aqu
Braley, R.D ., ed. 1992. Manual for the culture of giant clams Part 1. Ha
Monograph No. 15, 144 p.
AClAR 1986. Giant clam project, 4th Report. James Cook University of
--Referenfes
CLAMS
redators and parasites of giant clams (Bilvalvia: Tridacnidae) in the
olinao, Pangasinan. In: Zaragosa, E.C., de Guzman , D.L, and
he symposium-workshop on the culture of giant clams (Bivalvia:
maguete City, 75-80.
mul, J.O. 1985. The gastropod Cymatium muricinum, a predator on
e, 48, 211-221.
idae in the Indo-Pacific. lndo-Pacific Mollusca , 1(6),347-359.
evolution of Tridacnidae (Giant Clams). Archives de Zoologie
1-40.
destructive to economically important molluscan beds and coral reefs
eries, 26(1-2), 163-200.
ce of shell-boring polychaetes and sponges on pearl oysters Pinctada
ms. Proceedings of the Symposium on Coastal Aquaculture, 2,
Sources:
AClAR 1986; Crawford et al. 1988; Gomez and Belda 1988;
Estacion 1988.
1.3
3.8
3.6
2.9
2.6
1.3
Bindoy, Negros Oriental
Dumaguete City, Negros Oriental
Carbin Cay, Sag ay, Negros Occidental
Balicasag Island, Bohol
Pamilacan Island, Bohol
Donajon Bank, Bohol
Tridacna gigas
5.3
Apo Island, Negros Oriental
Hippopus hippopus
Tridacna derasa
6.0
Silaqui Island, Pa
Orpheus Island,
Australia
Apo Island, Negr
Carbin Cay, Sag
Silaqui Island, Pa
Apo Island, Negr
Silaqui Island, Pa
Santiago Island,
H. hippopus (cont'd)
4.5
2.8
2.3
San Juan, Siquijor
Dumaguete City, Negros Oriental
Silaqui Island, Pangasinan
Papua New Guinea
Tridacna squamosa
Locality
Growth rate
(mm/month)
Species
Locality
Species
Growth of five species of giant clams during ocean nursery and growout culture at various locations.
Re(orded growth rates of giant (lams
--Appendix