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TOLERANCE, SURVIVAL RATE AND GROWTH OF TILAPIA (Oreochromis niloticus)
FINGERLINGS AT DIFFERENT SALINITY LEVELS
NTABO JANET K.
FIS/38/09
SPECIAL PROJECT SUBMITTED IN PARTIAL FULFILLMENT FOR THE
REQUIREMENTS FOR THE AWARD OF BACHELOR OF SCIENCE IN FISHERIES
AND AQUATIC SCIENCES OF MOl UNIVERSITY
5th April, 2012
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DECLARATION
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By the candidate:
I hereby declare that this dissertation has not been presented in any other institution and is my
own original work.
NTABOJANETK.
FIS/38/09.
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Signature
Date
By the supervisor(s):
I hereby declare that this dissertation has been submitted with my approval as University
supervisor.
DAVID MANGUYA LUSEGA.
Department ofFisheries and Aquatic Sciences
P. O. Box 1125
Eldoret - Kenya
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DEDICATION
To my family and those who made it possible for me to achieve this.
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ABSTRACT
The shortage of fresh water in many countries, together with the competition requirement for
agriculture and other urban activities has increased the pressure to develop agriculture in
brackish water and sea water. Tilapia is excellent candidates for aquaculture in brackish water
due to their ability to tolerate a wide range of water salinity. Salt tolerance depends on tilapia
species, strains and size, adaptation time and method and environmental factors. To develop a
simple and accurate index of the salinity resistance of tilapia, batches of 30 fmgerlings (6 to 10
g) of Oreochromis niloticus reared in fresh water were subjected to gradual increase in salinity.
Fish were acclimatized in graded series of salinities after every two days. The mortality,
monitored on a daily basis, appeared after 2-5 days with no deaths in the rest of the 11 weeks
depending on the increment of salinity. The higher the daily rate in salinity increase, the shorter
the time lapse before total mortality occurred. Growth at 10ppt and above was significantly
higher than that of 5ppt and there was a clear increase in growth with salinity.
iii
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Table of Contents
DECLARATION
DEDICATION_._
I
_
_ _
__
_11
LIS'f OF TABLES
..
.
_ .._ _ .._
_ .._
LIST OF FIGURES
VI
VII
LIST OF PLATES
VIII
LIST OF ABBREVIATIONS AND ACRONYMS
IX
ACKNOLEDGEMENf .._ _•__•__. _ _ _._ _._
_
_
_._
_
_ ..__.. X
CHAPfER ONE
1
1.0
INTRODUCTION
1.1
TILAPIA TOLERANCE
1.2
PROBLEM SfATEMENf AND JUSTIFICATION_
1.3
OBJECTIVES
2
1.4
RESEARCH HYPOTIlESES
2
1
_
_ _
1
_ _ .._
_ .. 2
CHAPI'ER lWO
2.0
3
LITERATURE REVIEW.._ _ _ _
__ _._
__
_
_
_
3
CHAPfER THREE
7
3.0
MATERIALS AND METHODS
7
3.1
STUDY AREA
7
3.2
FISH COLLEC110N __..__
3.3
MEASUREMENTS
7
3.4
EXPERIMENTAL PROCEDURE
8
3.5
EXPRESSION OF TIlE RESULTS AND STATISTICS
8
DATA ANALYSIS
9
3.6
__
._ __.._
CHAPfER FOUR
4.0
4.1
4.2
4.3
_
_
__ 7
11
RESULTS
11
CONTROLS AND 5PPT
FINGERLINGS AT lOPPT AND 2OPPT
11
13
WATER QUALITY PARAMETERS
14
CHAPTER FIVE
16
5.0
DISCUSSION
16
EFFECT OF SALINITY ON SURVIVAL AND GROWIH
16
MECHANISM OF SALINITY TOLERANCE OF O. NILOTICUS
17
5.1
5.1
CHAP'I'ER SIX
19
iv
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LIST OF TABLES
Page
Table 1: Treatment agent and its concentration tested during the experimental stages
9
Table 2: Summary of the averages of the salinities and survival rates
10
Table 3:Highest survival percentages ofthe fingerlings at different salinities at different exposure
times
11
'"
Table 4: Fingerlings Mean (±SEM) percent survival of Oreochromis niloticus in sodium
chloride treatments
12
Table 5: Model parameter statistics from the logistic regression (fingerlings
14
Table 6: Model parameter statistics from the logistic regression (lethal concentration) ...... 14
vi
LIST OF FIGURES
Page
Fignre 1: Predicted probability of Oreochromis niloticus fingerlings survival exposed to
sodium chloride for 12.24 and 48 hours at acclimation stage based on logistic
analysis modeL
12
Figure 2: Predicted probability survival of Oreochromis niloticus exposed to highest
concentration of sodium chloride for 48 hours at acclimation stage based on logistic
13
analysis model
Figure 3: Shows mortalities ofOreochromis niloticus during experimental period
15
Figure 4: Growth curves for 0. niloticus in different salinity levels in plastic buckets installed
in a greenhouse
15
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LIST OF PLATES
Page
Platel:Mortalities of Oniloticus fingerlings in the greenhouse at a concentration of 5ppt and
24
lOppt
Plate 2: Mortalities of Oniloticus fingerlings in the greenhouse at 20ppt
viii
25
LIST OF ABBREVIATIONS AND ACRONYMS
SEM-
Standard Error of the Mean
ppt
Parts Per Thousand
LC­
Lethal Concentration
LBM
Length before mortality
LAM
Length after mortality
ix
ACKNOLEDGEMENT
My sincere gratitude goes to the Director ofKMFRI, Dr Johnson Kazungu for giving me an
opportunity to pursue this degree course, my supervisor Mr David Manguya Lusega for his
tireless effort in ensuring that the work was done well and all the time going to the greenhouse to
ensme that everything went well, as well as making positive criticism of the entire write up.
Secondly I would like to thank Mr Julius Manyala for his positive criticism of this script and
giving suggestions, Proffessor Liti and Mr Josiah.In the same note I would like to thank the
following without whose support I could not come up with this project. Chief technician Mr
Kinyua, Mr Odhacha, Mr Andrew, Ms Mary, Mr Obiero, Mbaru, Kembenya and my colleagues
for their support in coming up with this project.
Lastly I would like to thank my family who patiently bore the pain of my absence from home to
accomplish this mission for their own good.
GOD BLESS YOU ALL!
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CHAPTER ONE
1.0
INTRODUCTION
1.1
Tilapia Tolerance
There is a very strong rationale for aquaculture of salt tolerant fish. Around estuaries, there is
less competition for water and land between agriculture and aquaculture. The water resources
available fOT inland aquaculture, particularly in arid areas are often in salt laden areas. Irrigation
of land for agriculture can also lead to salt accumulation in the soil to a point where agriculture
must cease. Incorporation of fish ponds into flushing schemes for desalination can help in the
rehabilitation of salt laden soils while also producing useful crop.
Many fresh water tilapias are moderately salt tolerant (Chervinski, 1982). Estuarine tilapias such
as 0. mossambicus are euryhaline (payne, 1983; Trewavas, 1983) Salt tolerance is often equated
with survival but in a production system, survival and good growth performance should be the
criteria. Tilapia has a threshold salinity beyond which growth (payne, 1983; Stickney, 1986) and
reproduction (Watanabe and Kuo, 1985) are inhibited.
For salt water tilapia culture, it is important to detennine these thresholds and to establish the
ways in which other factors influence them. Since changes in salinity affect osmoregulation (an
active process) one probable modifier is likely to be temperature. This paper describes a series of
tolerance performance assay of 0. niloticus fed on a commercial feed under different conditions
of temperature and salt concentration.
Numerous reports have been dedicated to acclimation of tilapias from fresh water to salt water or
salinity up to 70ppt (Potts et aI., 1967) They showed that tilapias tolerate a higher salinity after a
progressive transfer, also called multistep acclimatization, gradual increase or stepwise increase.
1
1.2
Problem Statement and Justification
The shortage of fresh water in many cOWltries, together with the competition requirements for
agriculture and other urban activities has increased the pressure to develop aquaculture in
brackish water and sea water. Tilapia are excellent candidates for aquaculture in brackish water
due to their ability to tolerate a wide range of salinity. Published reports indicate that tilapia
reared in seawater and brackish environments may require lower protein levels for optimum
growth than fish grown in freshwater. This study was therefore conducted to find the salinity
level at which Oreochromis niloticus showed better growth and maximum survival.
1.3
Objectives
The objectives of this study were to:
i) To detennine the level of salinity at which 0. niloticus survives.
ii) To ascertain the effects of salinity on growth of 0. niloticus.
1.4
Research Hypotheses
The research hypotheses for this study were:
110:
Salt tolerance does not depend mainly on adaptation time and method, species and
strains.
HA:
Salt tolerance depends mainly on adaptation time and method, species and strains.
110:
Pre-acclimation to salt water and gradual transfer to high salinity has no significant
effect on tilapia growth and survival.
HA:
Pre-acclimation to salt water and gradual transfer to high salinity has a significant effect
on tilapia growth and survival.
2
CHAPTERlWO
2.0
LITERATURE REVIEW
The literature concerning the tilapias demonstrates that the ability to live in salt water (i.e
tolerance) depends on the species, the mean individual weight, the method of transfer, the
feeding techniques for pre-acclimation, the physiological status of the fish and more generally
the effect of environmental factors(Chervinski,1982;Watanabe et al..1988; Suresh and
Lin,1992).The tolerance to salt water is often negatively correlated with the growth capacity. For
example, Oreochromis niloticus is considered to be a species which grows particularly well but
has very low tolerance to salinity. Conversely, species such as Sarotherodon melanotheron and
0. mossambicus which have naturally low growth capacities tolerate a salinity of 80-117g1-1 in
the wild which is considered to be among the highest levels known in tilapia species (Whitfield
and Blaber, 1979; Stickney, 1986; Green, 1997). Tilapia fishes, despite being fresh water, are
believed to have evolved from marine ancestors (Kirk, 1972) therefore most of these fishes are
able to tolerate a wide range of water salinity. They can grow and reproduce normally in
brackish water .Some species can even grow and reproduce at very high salinity .However
limited data are available on tilapia culture in brackish water and seawater compared to the
voluminous information available on their culture in fresh water environments. The global
freshwater shortage and competing requirements has increased the pressure to develop
aquaculture in brackish water and seawater. In Kuwait, tilapia production is only done in small
scale due to water limitation hence the re-circulating system is recommended to efficiently
utilize water. Since initially it was envisioned that tilapia would be produced only in seawater,
the most abundant resource in Kuwait, most studies done on grow out production is done only in
seawater;(Cruz and Ridha 1991; 1995; Cruz et al., 1990) and only spawning activities were
conducted in brackish water(2-4ppt) The environmental factors affecting tilapia in the wild or
under aquaculture conditions include salinity, temperature, dissolved oxygen, Ammonia and
nitrites, pH, photoperiod and water turbidity. Extensive work has been published on the tolerance
and adaptability of tilapia to water salinity and the suitability of salt water for tilapia culture. The
studies indicated that salt tolerance depends mainly on tilapia species, strains and size, adaptation
time and method and environmental factors (Chervinski, 1982; Philipart and Ruwet, 1982;
3
Suresh and Lin 1992). It has been reported that 0 mossambicus, 0 aureus and T zilli are the
most salinity tolerant tilapia species. 0 mossambicus can tolerate up to 120% water salinity
(Whitefied and Blaber, 1979). Moreover they can grow normally and reproduce at water salinity
of 49% and their fry live and grow reasonably well at 69% (Whitefied and Blaber, 1979).Other
tilapia are generally less euryhaline and can tolerate water salinities ranging from about 20-35%
including 0 niloticus. Most of these tilapia grow, survive and reproduce at 0-29%0 depending on
the species and acclimation period. Salinity tolerance of tilapia is also affected by fish sex and
size. Perschbacher and McGeachin (1988) evaluated the salinity tolerance of red tilapia (0
mossambicus) fry juveniles and adults. Adult fish were more salt tolerant than fry and juveniles.
Fry and juveniles tolerated direct transfer to 19%0 without apparent stress and mortality, but
1000;. mortality occurred at 27%o.On the other hand adult fish tolerated direct transfer to
27%owith 100% mortality at 37%0.Similarly, Watanabe, et al (1985) studied the ontogeny of
salinity tolerance in Nile tilapia, blue tilapia and hybrids of tilapia O. mossambicus female x 0
niloticus male. The Median Lethal Salinity -96h(MLS-96) for Nile tilapia and blue tilapia over a
period of 7-120 Days Post Hatching(DPH) was 18.9 and 19.2%o.In contrast MLS-96 of tilapia
hybrids changed with age and increased from 17.2%0 at 30 DPH to 26.7%0 at 60 DPH. The
authors associated these ontogenetic changes in salinity tolerance to body size than to
chronological age. Watanabe et al (1985) reported also that male tilapia tend to be more salt
tolerant than females. Water salinity has also been reported to affect reproduction of tilapia
where gonadal development and spawning of tilapia occurred at salinities of 17-29%owhile the
onset of reproduction was delayed with increasing water salinities of 25-50%0 and reproduction
stopped completely at salinity above 30%0 (Fireman-Kalio, 1988).On the other hand Watanabe
and Kuo (1985) found that the total number of spawning of Nile tilapia females was greater in
brackish water (5-15%0) than in either full strength seawater (32%0) or fresh water.
It bas been reported that tilapia hybrids descended from salt tolerant parents (such as 0
mossambicus and O. niloticus) Suresh and Lin, 1992; Romana-Eguia and Eguia, 1999. This
explains why Taiwanese red tilapia (Liao and Chang, 1983) and Florida red tilapia (Watanabe et
al., J988) grow faster in saltwater and brackish water than freshwater. Pre-acclimatization to
saltwater and gradual transfer to high salinity have a significant effect on tilapia growth and
survival, as reported by Al-Amoudi (1987). It was found that 0 aureus, 0 mossambicus and 0
4
spiluros required shorter acclimatization time (4 days) for a transfer to full strength saltwater
than 0. niloticus and 0. aureus x 0. niloticus hybrids (8 days). These results indicate that the
former tilapia group is more euryhaline than the latter group. The earlier eggs and fry are
exposed to high salinities, the higher the survival (Watanabe et at., 1985b) and prolonged
acclimation over days, or even weeks from freshwater to saltwater increases survival. It has been
recognized that some tilapia may have higher survival with higher growth in saline conditions
than in fresh water. The Florida red tilapia is one variety that exhibits superior survival growth at
elevated salinities Oreochromis aureus has been shown to reproduce in salinities as high as
9ppt, grow in salinities of 36ppt and die at 53 ppt (Chervinski and Yashour, 1971). 0. niloticus is
widely accepted as a culture species
due to its rapid growth (Mair, 2000) but its salinity
tolernnce is comparatively low, about 20-25 ppt (Watanabe et aI., 1985a)Similarly the
physiological responses to 0. niloticus to saltwater have been evaluated by Morgan et al. (1997).
Fish reared in freshwater were transferred to freshwater, isotonic salinity (ISO 12%0) and 75%0
seawater (25%0) and a number of physiological parameters were measured. It was found that
plasma Na+ and CI- were elevated one day after transfer to saltwater but returned to freshwater
levels on day 4. Plasma cortisol and glucose levels were higher; while growth hormone,
Na+ATPase activities and prolactins were lower in freshwater and ISO than in seawater.
Mechanisms that allow tilapia to tolerate elevated salinities have also been investigated. Its
believed that tilapia developed from a marine teleost ancestry and that the mechanism that allow
for salt tolerance in some species are based in this ancestry (Allanson, 1971) Chloride cell
proliferation in gill filaments along with increased Na+IK +ATPase activity when fish are
subjected to elevated salinity levels apparently enhances tilapia survival under saline
conditions(Avella et aI., 1993)It has been suggested that chloride cell counts and elevated blood
levels of Na+IK +ATPase, an enzyme used in salt regulation are indications of salt tolerance in
tilapia (Avella et al., 1993).Other mechanisms that may aid in salt tolerance in 0. niloticus
include a secondary haemoglobin type that develops 47 days after hatching. This haemoglobin
molecule has been reported to have better affmity for oxygen at elevated osmotic and
temperature levels than in the conventionally recognized haemoglobin. This secondary
haemoglobin could transfer oxygen at elevated salt levels when conventional haemoglobin could
be less effective.
5
It has been reported that the metabolic rate of tilapia increases with increasing water salinity
(Bashohideen and Parvatheeswararao, 1976). Despite that the economic potential of tilapia
cultme in saltwater has not been well investigated, the available information revealed that rearing
these fish in sahwater environments can be cost effective if proper management measures are
adopted. Head et al. (1996) found that feed, processing and distribution and sex reversed fry
represented the highest variable costs in commercial scale, seawater pond production.
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6
CHAPTER THREE
3.0
MATERIALS AND METHODS
3.1
Study Area
This study was conducted at Moi University, Chepkoile1 Campus specifically at the Fish fann
(Department of Fisheries and Aquatic Sciences) greenhouse in January to March 2012. The campus is
located 9 kIn North East of Eldoret Municipality on the Eldoret- Ziwa road. It is in Eldoret town, Uasin
Gishu District of Rift Valley province. Eldoret town is positioned at Latitude 0° 35° N and Longitude
35~ 12° E at an altitude of2180 m above the sea level. Accordingly 8 containers (non toxic basins)
were used and were labeled according to the salinity levels (Oppt. 5ppt. IOppt 2Oppt) in replicates
.Fresh water was obtained from the tap which is supplied from local Municipal supply and was
placed in a 1000 tank and left in the sun for 2 days to allow residual chlorine to evaporate. The
salt for salinity was Itkg of commercial sea salt which was used for the whole experiment.
3.2
Fish Collection
Tilapia fingerlings (Oreochromis niloticus ) of size (6 g and 5.5 em) by net casting from
different ponds at the Chepkoilel Fish farm and placed in freshwater holding tank. They were
acclimatized to salinity of 5ppt before distributed for 8 hours before they were placed in the
experimental cylinders in the greenhouse.
3.3
Measurements
The temperature was measured to the nearest 0.1 C with a calibrated mercury thermometer. The
salinity (±O.t g-I) was monitored with a salinometer-conductimeter. The pH meter used (±O.t)
was the laboratory model (Hanna Instruments, Model 85t9, USA) Dissolved oxygen was done
using Winkler Method. A balance model KERN EG balance 420-3NM accurate within 0.01 g
was used to weigh the fIsh.
7
3.4
Experimental Procedure
A group of 240 fingerlings of Oreochromis niloticus (mean weight:6-20 g) were stocked to the
their respective salinity containers of Oppt (control) 5ppt,lOppt and 20ppt respectively in
replicates. The weight and standard length of each fish were measured before stocking. 50g
(5ppt) of sodium chloride was dissolved using the water in the experimental bucket from each
container and the brine solution poured into each container, 30 fmgerlings which were not fed
were captured and randomly distributed into each tank and each treatment replicated 3 times
including control in 10 litres salt water. This random distribution of fish was stopped when each
tank contained 30 fish. The fmgerlings were then acclimatized to their fIrst salinity of 5ppt for 8
hours the first day.
Fish were acclimatized to the respective treatment salinities by raising the salinity at the rate of 5
ppt every 2 days till the last container was 20 ppt. Fish were hand fed to satiation twice daily
(0800 hours and 1500 hours) on a commercial tilapia diet (30% protein and I% lipid) . Air
temperature was measured in and outside the green house as well as water temperature 3 times
daily. pH was measured using pH meter on daily basis while DO was measured using Winkler
Method. After every 3 days the water was replaced and, uneaten food siphoned .. During this
operation., the behavior of the fIsh was observed and the mortality (number of fish died within
the previous 24 h) was monitored. The dead fIsh were removed and counted in each tank. The
test of salinity ended when there were no mortalities in each tank and there was signifIcant
increase in weight and length.
3.5
Expression of the Results and Statistics
The mean and standard deviation of the water quality variables (Temperature, pH, Dissolved
Oxygen) were calculated for each test and for the entire series of tests. For each tank the data on
mortality and salinity versus time were expressed as the mortality versus salinity (number of
dead fish observed after a 24- hour period at a given salinity) and plotted as the predicted
probability survival rate (Probit)- (mortality in %) against the change in salinity. The curves of
the probability survivals from 100% to 0% versus salinities were drawn and the equations of
8
their linear regressions and their correlation coefficient r2 were calculated by Microsoft Excel
software. These calculated for each experimental condition using the 4 MLS values of the
replicates.
3.6
Data analysis
The data from the experiment consisted of the number of fmgerlings in each tank that survived at the end
of the experiment. Since the survival success is a binary variable, which should follow a binomial
distribution a logistic analysis was performed (Agresti, 1990) on the data by fitting the logistic model.
The logit model is a general logistic model as shown below:
log i1[O(z)] =
IOg[ 1 ~~~ )] = po +
PIZI
JoJ
-.L] = po + PIC + P~~2 + PlCl
ll-P
+ P2Z2 + ..,+ PiP
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Is a general logistic model, which takes the form of equation 2 in dose
probability of survival,
Po is the
intercept,
Equation 1
treatments~
where p denotes the
P2 is the coefficient of quadratic response
in C2 and P3 is the
coefficient ofcubic response in Cl .
The model parameter statistics are given on table 5 and 6 Mean (SEM) percent survival of fish
fUlgerlings subjected to varying concentrations of sodium cWoride and exposure times are shown in
tables 1, 2,3 and 4 while figures 1, 2 and 3 present the predicted probability of survival of fingerlings. As
shown in figure 1, 2 and 3 treatment of fingerlings with sodium cWoride significantly affected the
probability offish survival. The logistic regression model fits the survival data adequately.
Table 1:
Treatment agent and its concentration tested during the experiment (ppt) fmgerling
stages
Treatment agent
Range of concentration tested (ppt)
Acclimation stage (Nacl)
Stocking stage (Nacl)
Monitoring stage (Nacl)
Oppt,5ppt
5ppt, lOppt
Oppt,5ppt, lOppt, 20ppt
9
Table 2:
Summary of the averages of the salinities and survival rates
Concen1ration
SUMMARY
Groups
Count
Sum
Meah
Sld Err
10ppt
4.415
0.218143
3.661667
0.172324
4.825
0.187816
Avemge
Variance
20ppt
Con1roI
34
168
4.941176
2.586132
5ppt
5ppt
34
172.1
5.061765
2.247888
Control
4.646667
0.203201
10ppt
34
157
4.617647
3.293619
Grand Total
4.387083
0.101573
20ppt
34
141.2
4.152941
2.548021
df
US
F
P-wlue
Fait
2.101638
0.103078
2.673218
ANOVA
Sofm;e of Variation
SS
Between Groups
16.82728
3
5.609093
Within Groups
352.2968
132
2.668915
369.124
135
Total
CHAPTER FOUR
4.0
RESULTS
4.1
Controls and 5ppt
The results showed that concentrations of Sodium chloride of 5ppt gave survival percentages of
more than75%, which were higher than the treated control ( Oppt). However treatment with
sodium chloride at lOppt improved the survival rate with high mortalities recorded at
concentration of 20ppt in the first week. .
Table 3: Highest survival percentages of the fingerlings at different salinities at different
exposure times
Exposure time
Optimum concentration
Highest survival percentage
12 hours
5ppt
75%
24 hours
10ppt
50%
48bours
20ppt
40%
Generally 8 hours acclimatization gave the highest percentage of survivors compared to the other
exposure times of 12 hours and 24 hours. Survival for 24 hours gave lower values compared to
12 and 24 hours. The highest percent survival for 48 hours was observed at 5ppt where (75%) of
the fingerlings survived. For 24 hours exposure time the highest percent survival was observed at
10ppt where 50% of the fingerlings survived. For 48 hours survival observed at 20ppt was 40%
far below the expected range..
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\\::~
11
~'l
~,J'«'~~
~.!l~ 'V~j"
~'-'" JJ
.<.r:> ~
("T
'
~
'1
',.(\
'",":.!.l'",
...." ....,~i
~.
<
.
••:
, •.~
•
f
.p
.'
loP
~:'C
~/!
, •
r:
. '.
,.x­//
.":.,~~;,.~::,. ;~:;.;) ......"''' ..
'
Table 4: Fingerlings Mean (±SEM) percent survival of Oreochromis niloticus in sodium
'chloride treatments
COKeDtratioD (ppt)
Exposure time
12 hrs
24 hrs
48 hrs
0
22.7 ±0.6
20.7 ±0.6
14.3 ±3.2
5
30.7± 0.6
27.3± 2.3
23.7 ±0.6
10
29.7± 0.6
32.7 ±1.2
30.7± 0.6
20
38.7 ±0.6
40.7 ±0.6
39.8 ±1.5
Predicted probability survival
~
.;;;;.;;;.-~-::.
O. j-
__.. __
0.8
- ..... .......
/ ' .--,
0.7
I .... ·
....
"',
/
'.'"
'. , "- ...
0 . 6 ·, ' '
0.5 .
,:
"
0.4
0.3·
'
0.2
0.1
o
o
- - 1 2 hours
......
,
- - - - 24 hours
...... ·48 hours
'\
...
, ,
. ,
'. , ' .... ....
'::-:,
-',
5
10
20
15
25
Concentration (ppt)
Figure 1: Predicted probability of Oreochrom is niloticus fmgerlings survival exposed to
sodium chloride for 12,24 and 48 hours at acclimatization stage based on logistic
analysis model
12
4.2
Fingerlings at lOppt and 20ppt
The results for the fingerlings showed almost the same trend as the ones in the controls but
differed slightly with increase in exposure time. One interesting observation for fingerlings was
observed at 48 hours where they performed better than those in the controls. The results showed
that concentrations of sodium chloride ranging from 5-l0ppt gave survival percentages of over
70%, which were higher than the control (Oppt). However treatment with sodium chloride at
more than lOppt reduced the survival rate with total mortalities recorded at concentration of over
10ppt. Concentrations more than 5ppt gave low survivals.
Predicted probabllltv survival
o.~ ~
i
0.8
0.7 '
0.6
0,5
0.4
0,2
0.3
~----
•.. ~f"':- -
/
..
./
---.' ....
'"
\,
'.
...... ·24 hours
./
- - 4 8 hours
,•••• , \
i
.. \
1
0.1o
'.
\
0···\
I
5
20
10
25
Concentration (ppt)
Figure 2:
Predicted probability survival of Oreochromis niloticus exposed to highest
concentration of sodium chloride for 48 hours at acclimatization stage based on
logistic analysis model
13
4.3
Water Quality Parameters
To assess the kind of conditions the fingerlings were subjected to during the experiment water
quality parameters were monitored throughout the experiment though they were not part of the
objectives of the experiment. Temperature, dissolved oxygen, pH and total ammonia nitrogen
monitored. The means of these variables were 26±2oC, 6.8-7.7, 6.6-7.3 and 0.27±O.08mg/1
respectively. Temperature was measured using a thermometer, dissolved oxygen measured using
the Winkler meth<XL pH measured using a pH meter (Hanna Instruments, model 8519, USA).
The water volume was maintained at 10 litres of saltwater with the fmgerlings that survived the
salinity throughout the acclimatization and monitoring period.
Table 5: Model parameter statistics from the logistic regression (fingerlings)
fingerings
Time
Chemical
hours)
Sodium
chloride
12
24
48
----- --
-----
-
Model
Parameter significance (p-vakle)
log (p/1-p)=5.3750E-01 + 1.3892E-02*C-1.2601 E-04*C2 +
130 (0.0000) ~1 (0.0000) ~2 (0.0000) Ih
2.3307E-08*C3
(0.0003)
log (P/1-p)=5.0477E-01 +1.6295E-03*C-1.9294E-o6*C2+
130 (0.0000) ~1 (0.0000) ~2 (0.0000) Jh
5.0421E-10*C3
(0.0000)
log (pl1-p)=6.0141E-01 +8.0oo1E-04*C-1.2258E-06*C2
130 (0.0000) 131 (0.0053) 132 (0.0013) 133
+3.3984E-10*C3
(0.0054)
.-----------
------
---
--
---
--
-
--
--
-
- .­
Lethal
Canctntration
concentra
Chemical
Sodium chloride
tion
0-10 ppt
20ppt
Model
Parameter significance (p-valJe)
log (p/1-p)=3.9937-o1 +9.7175E-01*C-1.1937-o3*C2 +­
130(0.0000) ~1 (0.0002) ~2 (0.7304)
4.6222E-05*C3
Ih (0.0065)
log (P/1-p)=4.1365E-01 + 1.6251 E-01 *C-o.0221 E-02*C2
130 (0.0000) ~1 (0.0024) lh (0.0088
+6.0444E-10*C3
Ih (0.0815)
14
Mortalities of O.niloticus during the monitoring period
30
25
.
20
E
15
CII
.a
~control
. . . .sppt
:II
C
10
:l
-..-10ppt
~20ppt
a
1
I
2
- - - - - - - - i
3
4
I
5
i
6
i
7
i
8
9
10
11
-
-,
12
WEEKS
Figure. 3: Predicted probability survival of Oreochromis niloticus during the experimental
period.
Changes in weights with time at different salinity levels
90
80
70
liIil
Vl
60
~ 50
~control
.!!
.. 40
. . . .sppt
:i
r
30
-.-10ppt
20
~20ppt
10
0
0
2
4
8
6
10
12
WEEKS
Figure 4: Growth curves for 0. niloticus at different salinity levels in plastic buckets installed in
a greenhouse
15
CHAPTER FIVE
5.0
DISCUSSION
5.1
Effect of salinity on survival and growth
The objective of the study was to define the salinity tolerance of Oniloticus fingerlings and
growth at different salinities. Based on the study of Watanabe et al (1985),when transferring a
given age group ,male tilapia will tend to be larger than females and more salt tolerant, though
that was not addressed in my study. On the basis of the study, fmgerlings had to withstand direct
transfer to 5ppt and feeding resumed after one day. Transfer to salinities above these levels will
require prior acclimatization for which a safe and convenient salinity is 5ppt.Watanabe et al
(1985) found that salinity tolerance after direct transfer from freshwater of 0. niloticus also
increased with age beyond day 7 according to the measurements taken as a function of body size
not age. Their results with 10-20 fish equivalent in weight to fry and juveniles in their study
revealed no mortality at test salinities of 20ppt and 17.5ppt respectively and total mortality at
25ppt and 32ppt respectively. In contrast to my study with 30 fingerlings there were mortalities
at Oppt,5ppt, lOppt and20ppt at acclimatization and after which no mortalities appeared for the
next 11 weeks. This could be attributed to handling stress as one of the reasons for sudden
mortalities Apparently, the response was very similar to that of Omossambicus, Kader et al
(1981) and Pange (1985) who reported no mortalities of juveniles following direct transfer from
freshwater to 20ppt with total mortality at 35ppt.
Salinity on the other hand has a significant effect on growth (fig 4).Tilapia even the less saline
tolerant Oniloticus ,appeared to grow well at 20ppt than in freshwater as was noted by Suresh
and Lin (1992).One major factor in the interpretation of these results is that this research was
carried out at fixed salinities whereas brackish water aquaculture is carried out at variable and
fluctuating salinities associated with tidal flows, rainfall and seasonality of salinity. From my
study conducted and from the graphs the optimum range of survival of o.niloticus is 5ppt
16
5.2
Mechanism of salinity Tolerance of O. niloticus
The chloride cells of the gill epithelium are the major site for osmoregulation in fish both for
uptake in freshwater and saltwater excretion in saltwater (Foskett and Scheffey, 1982; Uchida et
al., 2000). It should be noted also that prolactin secretion is suppressed during acclimatization to
saltwater, thereby facilitating salt excretion (Ayson et aI., 1993). The results in 0. niloticus were
in accordance with the fact that an increasing number of chloride cells become activated with the
rising salinity (Prunet and Bornancin, 1989), allowing the fish to excrete Na+ and cr ions from
plasma with a high efficiency up to a salinity of 20ppt before the mortality appeared. This
salinity is probably the limit of salinity tolerance of 0. niloticus. Beyond this salinity, the ion
secretion was probably insufficient to maintain the ionic balance and the increase of plasma Na+
and
cr concentrations led
to a lethal elevation of blood osmolarity (Avella and Doudet, 1996;
Sardena et aI., 2004) and cellular necrosis made the fish unable to withstand extreme salinities
(Sardella et aI., 2004)
In 0. niloticus, exposed to a daily salinity stepwise from 5ppt to 10ppt Iday the limit of salinity
tolerance seemed to be at 20ppt and the Mean Lethal Salinity (MLS) value observed was less
than anticipated. When the daily increment of salinity was above 10ppt per day, 0. niloticus had
a significantly lower MLS (P>O.05) which may be attributed to an incomplete development or
activation of the chloride cells with the increasing salinity. In the range 5-10ppt Iday, the higher
the salinity increment the lower the MLS, as there was likely insufficient time for the synthesis
of diverse enzymes (ATPases) and cellular structures responsible for the transfer of ions
(Fishelson, 1980; Boeufand Prunet, 1985; Jonassen et al., 1997; Morgan and Iwama, 1998). At
20ppt majority of fish survived in the four replicated tanks.
The rilapia, even the less saline tolerant 0. niloticus, appeared to grow as well as or better at
extreme salinities than in freshwater as was noted in the results. Finally, the higher value ofMLS
in the shorter time was obtained in 0. niloticus at a daily increment of 5ppt which can be
considered as the optimal daily increase in salinity to obtain sufficient osmoregulation. It is
17
lower than the daily rate of increase in salinity of 5 g
rl
day recommended by Watanabe et al.
(1990) as the optimal for the acclimatization oftilapias to sea water, depending on the objectives
whether it is short-term versus long-term acclimatization.
18
CHAPTER SIX
6.0
CONCLUSION AND RECOMMENDATIONS
6.1
CONCLUSION
Change in salinities only affects Oreochromis niloticus sUlVival at initial days before
acclimatization, otherwise the fish can survive at salinities of up to 20ppt effectively.
After acclimatization, the chances of survival for Oreochromis niloticus were high with
all the salinity levels tested.
The mortalities observed were mainly attributed to stress as the salinity increases did not
show effects after acclimatization.
Stepwise acclimatization is an important process in ensuring survival rates during transfer
of 0. niloticus from low salinities to elevated salinities.
6.2
RECOMMENDATION
Brackish waters of up to 20ppt should be considered as suitable environment for rearing
0. niloticus.
Aquaculturists should be advised on the method and importance of acclimatization of 0.
niloticus to reduce stress that can lead to increased mortalities during stocking in elevated
salinities. Its therefore recommended that the hybrid be further evaluated in a range of
real brackish water environments such as shrimp ponds before widespread adoption is
considered,in order to confirm the fmdings of this study under more realistic conditions.
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Al-Amoud,M.M,El-Sayed,A-F.M.& El-Ghobashy,A.(1996) Effects of thermal and thermo-haline
shocks on survival and osmotic concentration of the ti1apias Oreochromis mo.ssambicus
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on Tilapia mossambica Peters (Cichlidae).2.Changes in serum osmolarity,sodium and
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Avell~.,Doudet,T.,1996.Physiological
adaptation ofOreochromis niloticus and o.aureus to
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&eshwater euryha1ine te1eost,.Zool. Tilapia mossambica AnzJena 197 (112),47-56.
Boeuf ,G.,Prunet,P.,1985.Measurements of gill (Na+ l<.+)-ATPase activity and plasma thyroid
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.(Eds) .The Biology and Culture of Tilapias, ICLARM Conference Proceedings,vol. 7.
International Centre for Living Aquatic Resources Management Manila,Phillipines, pp..
119-128
20
Pange,A.D.1985.Branchial Na+K+ ATPase activity during osmotic adjustments in two
freshwater euryhaline teleosts,tilapia (Sarotherodon mossambicus) and Orange chromide
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(1983) Estuarine and salt tolerant tilapias.In:Fishelson,L.and Yaron,Z.(eds)
Proceedings of the International Symposium on Tilapia in Aquaculture.Tel-Aviv
University,Israel,pp.S34-543.
Payne,A.1.,Collinson,R.1.,1983.A comparison of biological characteristics of Sarotherodon
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Nile.Aquaculture 30,335-351
Payne~.I,Ridgway,J.
& Hammer,lL. (1988) The influence of salt (NaCl) concentration and
temperature on the growth of Oreochromis spiru/us, Omossambicus and red tilapia
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the Second International Symposium on Tilapia in Aquaculture, ICLARM Conference
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pp481-487
Perschbacher, P.W. & McGeachin,R.B.(1988) Salinity tolerance of red hybrid tilapia fly,
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Perscbbacher,P.W.,1992.A review of seawater acclimation procedures for commercially
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22
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x
o.urolepsis
homorum)
exposed
to
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23
APPENDICES
Mortality
LAM
LBM
Grand
Total
StdDev of control
1.249463043
1.573990574
StdDev of 5ppt
0.881360617
1.454813751
StdDevof
lOppt
1.108788422
1.689732202
StdDevof
20ppt
0.88879173
1.334813091
1.55139586
1.488723548
1.608908454
1.222575565
PLATES
b
a
Platel:MortaJities of O.niloticus fingerlings in the greenhouse at a concentration of 5ppt
d 10ppt
24
sz