Download WHAT IS A FISH? - Two Oceans Aquarium

TABLE OF CONTENTS
INTRODUCTION ........................................................................................................... 2
WHAT IS A FISH? ............................................................................................................... 2
FISH SHAPES...................................................................................................................... 2
ORIGINS AND DIVERSITY OF FISHES ................................................................................... 3
CLASSIFICATION OF FISHES ............................................................................................... 4
1. BONY FISH ..................................................................................................................... 4
INTERNAL STRUCTURE OF A BONY FISH .......................................................................... 5
SCALES AND SLIME ......................................................................................................... 6
SWIMMING WITH FINS AND TAILS .................................................................................. 6
THE SENSE ORGANS ....................................................................................................... 7
FEEDING ........................................................................................................................ 8
HOW FISH BREATHE ....................................................................................................... 9
BUOYANCY IN WATER ..................................................................................................... 9
LIVING IN FRESH OR SALT WATER .................................................................................. 9
REPRODUCTION .......................................................................................................... 10
SEX CHANGES IN FISH .................................................................................................. 10
2. CARTILAGINOUS FISHES ............................................................................................... 11
EXTERNAL STRUCTURE OF A CARTILAGINOUS FISH........................................................ 12
CARTILAGINOUS FISH SKIN TYPES ................................................................................ 12
TAIL SHAPES ................................................................................................................ 12
INTERNAL STRUCTURE OF A CARTILAGINOUS FISH ........................................................ 13
FEEDING ...................................................................................................................... 13
FEEDING ...................................................................................................................... 14
REPRODUCTION OF BEARERS ........................................................................................ 14
3. JAWLESS FISH .............................................................................................................. 16
EXAMPLES OF FISHES FOUND IN THE OCEANS AROUND SOUTH AFRICA ............................. 17
1. COELACANTH ............................................................................................................... 17
2. SHARKS, RAYS, SKATES AND CHIMAERAS ...................................................................... 17
3. REEF FISH .................................................................................................................... 19
4. PELAGIC FISH ............................................................................................................... 22
5. EELS ............................................................................................................................ 22
5.1 MORAYS ................................................................................................................. 23
6. SEAHORSES.................................................................................................................. 23
7. SUNFISH ...................................................................................................................... 23
CONSERVATION THROUGH RESEARCH AND OBSERVATION ......................................... 24
CONSERVATION VERSUS ECONOMIC FISHING INDUSTRIES ................................................ 26
1. OVERVIEW ............................................................................................................... 26
2. STATUS OF CERTAIN FISH STOCKS IN 2001 ............................................................... 28
Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH
Page 1
INTRODUCTION
WHAT IS A FISH?
A fish is a cold-blooded vertebrate that lives in water, breathes by means of gills and has fins for
stability and movement. Most, but not all fishes, have scales and a lateral line.
FISH SHAPES
Fishes can have many forms (see the illustration below). They can range in size from less than 1
cm (a goby) to over 12 m (a whale shark).
A. Lamprey
B. Hagfish C. Shark D. Ray E. Chimaera F. Lungfish G. Teleost
They do not include seals, whales and dolphins (mammals), turtles and sea snakes (reptiles) or
shrimps, lobsters, and crabs (crustaceans) or mussels (molluscs)
Some marine and freshwater invertebrates (animals with no backbone) and some animals with
shells (such as molluscs) are called ‘shellfish’. Therefore true fish may be called ‘finfishes’.
ICHTHYOLOGY is the study of the classification and the biology of fishes.
FISHERIES SCIENCE is the study of the management and utilisation of fish populations.
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ORIGINS AND DIVERSITY OF FISHES
The fish came first!
Ancient fishes first appeared in the fossil records over 500 million years ago, more than 100 million
years before any other vertebrate group. Fishes are therefore the most ancient, and all other
vertebrate groups (amphibians, reptiles, birds and mammals) evolved from them.
Fish first laid down the basic ground plan and functions of vertebrates.
These include the 10 organ systems:
skeleton, muscles, gills (respiratory), digestive, blood circulation, kidneys (urinary),
reproductive organs, hormone (endocrine) systems and the nervous system (including
the sensory organs), as well as the basic locomotion systems.
But fishes are not primitive because they are ancient. Some of them are very advanced and have
well developed senses of sight, taste, electro reception, vibration reception, in addition to
internal fertilisation, parental care, placental nourishment of the young, live birth,
learning and memory.
Many of the ‘inventions’ of man were first evolved by fishes, for example – echolocation, sonar,
camouflage, electro reception, electrical discharge and so on.
Fish species constitute almost 50% of all living vertebrate species and the extinct fish species
outnumber all other vertebrates.
Pie chart of living vertebrate species.
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CLASSIFICATION OF FISHES
Fishes like other animals may be classified based on the ancestral relationships and on their
feeding and breeding behaviour. This is known as Taxonomic classification.
The evolutionary sequence of fish is thought to begin with the jawless fish, then the
cartilaginous fish followed by the bony fish. The elephant fish shows characteristics of both
cartilaginous and bony fish. However, for practical purposes, as there are a greater variety
of bony fish than cartilaginous fish in the Two Oceans Aquarium, the bony fish are here
dealt with first.
The main groups of fishes that are described in the following pages are:
1. Bony fishes (Class: Osteichthyes) with a skeleton of bone such as lungfishes,
coelacanth, and all ray-finned fishes. Their bodies are usually covered with thin scales.
They have a single gill opening.
2. Cartilaginous fishes (Class: Chondrichthyes) with a skeleton of gristle or cartilage
such as sharks, chimaera, skates and rays. Their scales are buried in their skin. There are
several gill openings.
3. Jawless fishes (Super Class: Agnatha) such as hagfish, and lampreys that have no
jaws or scales. The skeleton is made of cartilage. There are several gill openings.
1. BONY FISH
As fishes live in water, a medium 800 times denser than air, and as water is buoyant they do
not have to support themselves, but density causes friction against their bodies so they have
to be streamlined.
EXTERNAL STRUCTURE OF A BONY FISH
Operculum (gill
cover)
Eye
Sight is well developed in most
fish and the eyes are most
sensitive to yellow-green the
wavelengths that penetrate
furthest into water.
Water taken through
the mouth is forced
out over the gills
beneath this cover.
In the process,
oxygen is absorbed
and waste products
released.
Dorsal fin
This single fin
acts as the
main ‘keel’
preventing
the fish
rolling during
swimming.
Nostril
Scales
These are
extremely thin,
overlapping bony
plates that protect
and streamline the
body. They contain
pigment cells,
although apparent
colour in many
fishes is produced
by reflected light.
Many fish have a highly
developed sense of smell.
The nostrils do not connect
to the mouth.
Mouth
Lateral line
The lines of dots
along the flanks are
tiny holes leading to
a canal that runs
the whole length of
the fish. Nerve
endings respond to
changes of water
pressure enabling
the fish to detect
vibrations in the
water.
Caudal fin (tail)
The shape and position varies
between surface, midwater &
bottom feeders.
Pectoral fins
(paired)
Fish use these to
steer and change
direction in the
water – even to
swim backwards!
Anal fin
Pelvic fins
(paired)
These also
help a fish
to control
its position.
Cloaca
(vent or anus)
This is the
opening for
urinary, digestive
& reproductive
systems.
This single fin acts as
a stabilizer during
swimming & in males
of certain species is
modified for breeding
purposes.
Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH
Most fish swim by
sweeping the back
part of the body from
side to side. The tail
fin helps to convert
that movement into
forward thrust.
Page 4
INTERNAL STRUCTURE OF A BONY FISH
The internal organs of a typical bony fish are packed into the cavity in the lower front half of the
fish. The rest of the body consists of muscles used for swimming.
1.
2.
3.
4.
5.
6.
7.
8.
eye
skull
brain
vertebral
column
dorsal spines
dorsal rays
lateral line
muscles
9. anal rays
10. anal spine
11. cloaca (vent or anus)
12. kidney
13. swim bladder
14. ovary or testes
15. intestine
16. stomach
17. spleen
18. pyloric caeca
19. liver
20. heart
21. gills
22. gill rakers
23. tongue
THE BODY SHAPES OF BONY FISH are adapted to their environment and this illustration
shows the terms used to describe their physical appearance.
1. Square in cross-section e.g. boxfish
and cowfishes.
2. Robust e.g. sea breams, rockcods.
3. Elongate, e.g. snoek and eels.
4. Compressed (that is flattened from
side to side e.g. butterfly fish,
moonfish, batfish.
5. Flat or depressed e.g. soles and
flounder.
Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH
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SCALES AND SLIME
The majority of bony fishes are covered with thin transparent plates called scales.
Scales are in fact outgrowths of the skin and provide the animal with a flexible covering that,
together with mucus (slime) secreted by the glands in the skin.
 forms a barrier to bacteria and fungal infection
 preventing the loss of body fluids (seals the body from osmoregulation).
Scales grow with the fish and the ‘annual rings’ are useful to determine a fish’s age and history.
1. Cycloid (smooth edged)
2. Ctenoid (rough edged)
3. Lanceolate (sharp and deeply
embedded in the skin e.g. marlins)
4. Rhomboid (not overlapping,
criss-cross pattern e.g. triggerfish.
Collection of fish for aquarium display:
Need to collect animals of the best physical quality to display in exhibits.
Hake cannot be displayed because it is difficult to catch them from the harbour wall. If anything
disturbs the slime covering the skin of the fish – the flesh disintergrates. Similar problem in
collecting snoek.
Sardines shed their scales to escape from predators. Scales are shiny and confuses predators.
Precautions taken during collection to prevent damage to scales and slime:
 Fish caught on hook and line rather than using nets as it damages the surface of the fish.
Hooks used are barbless.
 Stretcher is then placed into water to scoop the animals out or plastic bags. The stretcher is
kept as smooth as possible to reduce abrasion – seams are on the outside.
 Plastic bags and wet sponges are kept at hand in the event it is needed
 The collection
tank are made using fibre glass. These are made smooth using
sandpaper(?).
 The inside of all the collection tanks and those in quarantine have black lines painted on
them so that the fish can sense their boundaries and not bump into the sides.
SWIMMING WITH FINS AND TAILS
(a) FINS
Fishes can move in 3-D, forwards and backwards, left and right as well as up and down. They
wiggle through the water with a series of S-shaped waves. Their dorsal and anal fins act like keels
keeping them upright while the paired fins are used like oars to slow down or turn corners. A fin
has a thin layer of skin supported by fin rays, which may have stiff and bony spines or soft and
flexible (rays).

If the pelvic fins are set far back they are probably fast
swimming species.
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
Slower moving fishes that live on reefs for example have large
side fins, as they need to be able to manoeuvre around
obstacles.

If the pelvic fins are placed well forward, sometimes even
further forward than the pectorals, it is then typical of a bottom
dwelling hovering species.
(b) TAILS
The tail or caudal fin is, in many fishes, the main means of forward
propulsion and it uses the powerful muscles in the caudal peduncle with a
sweeping side-to-side motion.
Taking the shape of the tail and the general body shape is usually an
indication of the fish’s speed through the water. Faster, wide-ranging fish
such as mackerel and tuna have forked tails, which are hydrodynamically
more efficient than the rounded tails of the slow-moving fish such as kob
and rockcods.
1. Pointed.
2. Rounded.
3. Truncate.
4. Emarginate.
5. Lunate.
6. Forked.
THE SENSE ORGANS
Like us, fish can smell, see, taste and hear. They also have special sense to help them find their
way or search for food.
1. Seeing.
A fish’s eyes bulge out at the side of the head and it can see clearly to the front and detect
movement at the sides. Many fishes can see colour. They focus their eyes by moving the lens
not by changing the thickness of the lens as we do. Fishes have no eyelids as the water
constantly bathes their eyes.
2. Smelling.
A fish has a good sense of smell. Most fishes have a pair of nostrils that they use for smelling
not breathing.
3. Hearing.
Fishes have ears inside their heads, which pick up sound vibrations from the water. Some fish
use their swim bladder, like a drum, to magnify noises while others, the grunters, make loud
drumming noises which bounce back from rocks enabling them to find their way in murky
conditions. There are small bones in the ear called otoliths. The otoliths rest on sensory
pads and are used for balance, telling the fish whether it is upside down or on its side.
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4. Lateral Line.
Most fish have a lateral line running along each side of their body. Little holes in the line can
sense vibrations in the water, which may be made by other animals or waves bouncing off
obstacles or maybe sound waves. The lateral line is particularly helpful when fish swim in large
shoals or a predator approaches.
5. Tasting and feeling.
Some fishes have feelers or barbels on their chins, mouths or even fins. The fish uses these to
taste and search food.
6. Making and sensing electricity.
A few fish (such as the electric eel), can make electricity. They can sense anything that alters
the electrical field they produce. Coelacanths use electrical impulses to find food in the
darkness.
FEEDING
Fishes do not have regular meals. Some, like pilchards and sardines, constantly sieve plankton
from the water as it passes through their gills, while certain predators may go without food for
days or even weeks.
The shape and position of the fish’s mouth gives clues as to how it catches its food. Snoek have
ferocious sets of teeth and are predators on fish and squid. The mussel cracker has powerful jaws
and large grinding teeth used for crushing shellfish and sea urchins. The sea horse sucks in small
food items, while the teeth of a parrotfish are fused into a sturdy beak for nibbling hard corals.
The bones in a fish’s head are not usually fused together so the fish can move and expand its
head and jaws when feeding. Some fish blow small prey out of the sand.
In the illustration above the shape and position of a fish’s mouth can give clues to its feeding
behaviour or hunting strategy, for example:
1. The elongate jaws of fast-swimming surface carnivores e.g. Needlefish.
2. The protractile jaw (shown as retracted 2a and extended 2b). e.g. rockcods
3. The superior or undershot jaw typical of slow-swimming predators such as rockcods that
‘ambush’ their prey, but also of many other fishes including the fast-swimming pelagic wolf
herring.
4. The inferior or underslung jaw also typical of many fishes from anchovies to bottomdwelling barbels.
5. The terminal jaw where the mouth is at the tip of the snout typical of fishes, which nibble
or probe on the reef e.g. butterfly fish and wrasses.
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Fishes feed on a wide variety of foods, but the following major feeding groups are recognised.
Herbivores
Feeding mainly on plants - either phytoplankton, algae or higher plants.
Scavengers
Feeding on the remains of plants and animals, and associated organisms,
usually on the bottom.
Feeding on detritus and associated diatoms and bacteria.
Detritivores
Predators
Feeding on other animals, including zooplankton, other fishes, and
shellfishes. Worms etc.
Feeding on plant and animal food.
Omnivores
HOW FISH BREATHE
All animals from fleas to flamingos to fishes need oxygen in order to survive. On land oxygen is
contained in the air breathed into the lungs. Water dwelling creatures generally use gills to
extract oxygen that is dissolved in the water.
Water enters the mouth of a fish and flows out between the gills, which are richly supplied with
blood. Oxygen passes through the thin gill membranes and into the fish’s blood and is then carried
around the body.
Gill arches
Beneath the gill cover is a v-shaped bony arch. There are two rows of gill filaments with many
leaf-like folds to give a large surface area for absorbing oxygen. The surface area of the gills is 10
times the area of the fish’s body. Stiff gill rakers on the arch sieve food and debris from the water
before it passes between the gills.
BUOYANCY IN WATER
Swim bladders
The hydrostatic function of the swim/air bladder enables a fish to maintain the same weight as
the surrounding water it lives in, enabling it to float in the water without the tendency to either
rise or sink, exerting the minimal muscular effort.

As a fish rises the pressure in the surrounding water decreases and the gas in the bladder
expands. To counteract this and to restore equilibrium at the new level, gas is absorbed or
allowed to escape (depending on species).

Conversely, if the fish swims downwards, the hydrostatic pressure increases; the body
becomes heavier and tends to sink. By increasing the gas in the swim/air bladder the fish
is able to equalise.

Rapid exchange in external pressure of fish causes the gas in the air bladder to expand,
the body tends to shoot upwards, and the swim/air bladder is forced out through the
mouth. (See Barotrauma, page 4, AQUARIUM OPERATIONS).
Ragged tooth sharks do not have a swim bladder. Instead they take a gulp of air at surface to help
with buoyancy.
Precautions taken when collecting fish at depth:
 Bring fish up slowly to the surface to reduce barotrauma.
 If fish is experiencing barotraumas e.g. swimming lobsided obe it is brought to the surface,
determine where the swim bladder is positioned in the body of the fish – this is not the same
for each fish species
 Insert a hyperdermic needle into surface of skin and swim bladder to remove the excess air.
Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH
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LIVING IN FRESH OR SALT WATER
The saltiness of water has a great effect on a fish’s internal chemistry.
 Marine fishes tend to lose water to the salty sea surrounding them. They have to drink lots
of water and produce a little highly concentrated urine.
 Fresh water fishes on the other hand absorb water and must make large quantities of
dilute urine to remove the excess water.
A relatively small number of fish species (e.g. salmon, eels, grunter and moonies) are adapted to
live in both sea and fresh water.
Application for treating fish:
If fresh water fish are a bit stressed – aquarists may add a little more salt to the water.
REPRODUCTION
Almost all bony fishes lay eggs but there are two main
categories for reproduction:
 High numbers, small sizes of eggs.
Used by fishes living in unpredictable
environments to spread the risk widely in order to
increase their chances of having some of their
young survive.
 Small numbers, large sizes of eggs.
Used by fishes living in predictable environments
where there is strong competition from a large
number of species and they invest a lot of time
and energy in a few, large young.
There are three main breeding groups of fishes
Produce large number of small eggs released into the water column or on
Non-guarders
the bottom where they are fertilised. The parents abandon the eggs and do
not guard them.
Example : Herrings, catfish, kingfishes and most familiar fish.
Make a nest or burrow in which eggs, embryos, and/or juveniles are
Guarders
guarded until they are able to fend for themselves. They produce an
intermediate number of young.
Example : Bass, some tilapias, salmon, clown fish, steenjie.
Produce a few, very large eggs (coelacanth’s are the size of an orange)
Bearers*
which hatch either within the body, in the mouth or in skin pouches
(seahorse and pipe fish). These are only released into water once they are
well developed.
Example : sharks, rays, coelacanths, surfperches, some catfish
*Reproduction of cartilaginous fish - see next page
SEX CHANGES IN FISH
Sex change is common in many families of fishes including the rockcods, seabreams, wrasses,
parrotfishes, anemonefishes and damselfishes. Some species are able to change from female to
male and are known scientifically as protogynous hermaphrodites. Others change from male to
female and are known as protandrous hermaphrodites.
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Generally, sex change is regulated by population structure. On coral reefs, where space is limiting
and competition for prime spawning sites is fierce, species generally change sex from female to
male.
Why? In simple terms, it makes good sense to be a female when small and unable to defend a
spawning site. Small females can spawn with large dominant males for several years. When
older, the female may become sufficiently large to defend a site and, if the dominant male is
removed (usually by predation) she may change sex and become a male. Now ‘she’ can spawn
with many females and produce large numbers of offspring.
The simplest example of a fish changing from male to female is the anemone fish (clown fish).
The life of this species is linked to a single anemone. Its ‘world’ is rather small and, in this case, it
makes good sense to start off as a male and change to a female. Why? Generally, there is only
space for one breeding pair on an anemone. Males produce sufficient sperm to fertilize literally
hundreds of females so, in this instance, there is no advantage in being a large male. There is
however, a distinct advantage in being a large female – the larger the female the more eggs she
can produce! So the smaller fish of the pair is a male and the larger fish is a female. Should the
female be removed (by predation or disease), the male will become a female and an immature
fish, which has been waiting on the outskirts for this opportunity to arise, will come in and become
the male.
The examples given above are the most simple known to man. Sex change is more often a lot
more complicated than this, but it works for many species.
Which fishes in the Aquarium change sex?
Sea goldies (rockcods)
Yellowbelly rockcods
Red Roman (seabream)
Blacktail (seabream)
Red stumpnose
Clownfish
2. CARTILAGINOUS FISHES
Evolved about 450 million years from their bony fish ancestors. There are about 960 species in
cool and warm oceans worldwide of which about 300 species occur in southern Africa.
The two main groups are:
Sub Class: Elasmobranchii - Sharks, skates and rays with the upper jaw not fused to the skull,
teeth usually separate and 5-7 pairs of gill openings.
Sub Class: Holocephali – Chimaeras with the upper jaw fused to the skull, teeth in the form of
solid plates, and only one pair of external gill openings with a soft gill cover.
Important characteristics of cartilaginous fish:
 Gristle-like cartilage skeletons.
 A number of gill slits rather than a single gill opening.
 All males have claspers.
 Internal fertilisation.
 43% of cartilaginous fish (sharks and rays) lay eggs.
 Egg incubation periods vary from 1 to 15 months.
 Have true jaws and teeth and many species have rows of teeth, which move forward as
others break or wear out.
 Are primarily marine fish with some freshwater species.
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

Most have a highly developed sense of smell and are acutely sensitive to vibrations, which
they sense through their lateral line, allowing them to hunt their prey in very murky waters
where sight is not effective.
Maintain a high concentration of urea in their blood and other tissues so as to maintain the
ionic balance of their tissue relative to seawater.
EXTERNAL STRUCTURE OF A CARTILAGINOUS FISH
External structure of a
guitarfish
1. Eye
2. Spiracle
3. Tubercles
4. First dorsal fin
5. Second dorsal fin
6. Caudal fin
7. Pelvic fin
8. Pectoral fin
CARTILAGINOUS FISH SKIN TYPES
Cartilaginous fishes have placoid scales
which are not exactly like the ‘typical’
scales of bony fishes. The overlapping
pattern looks similar to scales but the
difference is that these are tooth-like and
each has a central core overlaid with
dentine and coated with enamel
Their skin is very rough and abrasive and
sharkskin (known as shagreen) has wide
applications and is still used in primitive
societies as ’sandpaper’ and to make nonslip handles on knives, spears and other
tools.
The four skin types here are from:
1. Tiger shark,
2. Dusky shark,
3. Sandbar shark
4. Lesser guitar fish
TAIL SHAPES
.
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Forward movement in sharks is the function of the tail. The shape of the tail can, in most cases,
give an indication of the speed of the fish.
1. The mackerel shark is the swiftest and its tail is a great sickle shape.
2. and 3. The grey and thresher sharks have robust tails giving them great speeds.
4. and 5. Caudal fins of the spiny dogfish and cigar sharks and are not as powerful.
6. Ragged tooth and hound sharks have a reduced lower lobe showing they are slower moving.
7. and 8 here the lower lobe is almost lacking in bottom-dwelling, and slow moving catsharks and
shysharks.
INTERNAL STRUCTURE OF A CARTILAGINOUS FISH
1.
2.
3.
4.
5.
6.
7.
8.
9.
nostril
eye
brain
spiracle
nerve cord
vertebrae
muscles
testis
first dorsal fin
Internal structure of a shark
10. dorsal spine
11. second dorsal fin
12. caudal fin
13. muscles
14. claspers
15. cloaca
16. pelvic fin
17. spleen
18. intestine
19.
20.
21.
22.
23.
24.
25.
26.
27.
spiral valve
pancreas
stomach
pectoral fin
liver
heart
gills
pharynx
mouth
Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH
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FEEDING
Cartilaginous Teeth
Although variations occur, the teeth of most
cartilaginous fishes usually fall into four categories
and it is possible to understand their eating
habits.
1. The great white and grey sharks have
triangular heavily serrated teeth suited to
cutting and tearing.
2. The tiger shark has slanted cocks-comb teeth
suited to cutting and tearing.
3. The ragged tooth shark has triple-cusped
pointed teeth suited to grasping and piercing.
4. Ray and guitarfish have round teeth that
provide a mill-like grinding action for crushing
mollusc and crustaceans.
How the jaws work
The jaw of many fast swimming sharks can
hardly be seen as it fits so neatly under the top
one allowing for a smooth profile. However,
when the mouth is open - the upper jaw seems
to dislocate therefore opening up the mouth to
its fullest extent.
REPRODUCTION OF BEARERS
Typical Life Cycles
There are three main
amongst the bearers
methods
of
reproduction
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Oviparous: The eggs develop and hatch outside the body of the female. The embryo, with an
adequate yolk supply, is encased in a leathery egg case called a ‘mermaid’s purse’ laid by the female
and attached to suitable material (e.g. seaweed) by coiled tendrils. A fully formed young shark hatches
from this case. Catsharks and shy sharks reproduce in this way and the egg case shown here is just one
example of various shapes laid by different sharks, skates and rays.
___________________________
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Ovoviviparous: Most common mode of reproduction where the
embryo hatches from an egg while still in the uterus. The young is
fed by a yolk sac before being born in an advanced state. Some
sharks and dogfish reproduce in this way.
____________________________
Viviparous: The embryo hatches from an egg and is
fed either by a placental connection or through a form of
uterine milk that bathes the embryo within the uterus.
Gestation period can vary from 2 months to 2 years before
free-swimming young are born. Examples of this are the
Great white and Hammerhead sharks.
3. JAWLESS FISH
Although many ancient and now extinct fish were ‘jawless’ the only surviving ones today are the
hagfishes and lampreys.
They are found in cool, temperate oceans in the Northern and Southern hemispheres. There are about
83 species worldwide and 4 species in southern Africa.
They have:




Cartilaginous skeletons and eel-like bodies with
no scales.
Paired rudimentary eyes and no true teeth or
vertebrae.
The gills are carried on the one edge of the gill
arches and are fused to the skull.
They have fins and a simple suction mouth.
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EXAMPLES OF FISHES FOUND IN THE OCEANS AROUND SOUTH AFRICA
1. COELACANTH
The coelacanth is the only surviving member of the ancient super-order of lobe-finned fishes, the
Crossopterygii. It first appeared in the fossil record in the Devonian Period 375 million years ago. The
earliest coelacanths lived in shallow fresh waters, but during the Mesozoic era these and many other fish
invaded the sea. Although fossils have been found on every continent except Antarctica, none date from
the time after the Cretaceous Period, 65 million years ago. For this reason the coelacanth was long
presumed extinct, until it was rediscovered in South Africa in December 1938.
Studies in the Comores have shown that coelacanths spend daylight hours in groups of up to 14 in
caves in the steep barren lava slopes of volcanic
islands. The caves lie at approximately 200 m
and the coelacanths can descend to 250-300 m
to feed on benthic fish. Females are larger than
males and are ovoviviparous. The eggs, the size
of an orange, are retained in the female’s uterus,
where they hatch and the female gives birth to
multiple live young. The largest specimens have
been 1.8m long and weigh 85 kg.
2. SHARKS, RAYS, SKATES AND CHIMAERAS
There are some obvious external differences that distinguish rays and sharks. Of these, the position of
the gill openings and the arrangement of the pectoral fins are most characteristic. Rays have their gill
openings located on the underside of the head as opposed to the lateral gill slits of sharks, and their
pectoral fins are enlarged into the typical flattened disc.
2.1 RAGGED TOOTH SHARKS
(Also known as the grey nurse shark & sandtiger sharks).
This shark is robust, extremely plump-bodied and has a pointed snout. The overall colour ranges from
light brown to grey with a pale underside. Large brown spots cover the body but these may fade with
age. Can attain 3m in length. Both jaws carry a few rows of long pointed teeth that it uses to pierce and
grasp the fish rather than ripping off a chunk like the Great White. A ragged tooth shark will have
approximately 20,000 teeth in its lifetime.
Their reproduction is different to other ovoviparous sharks in that the ovary and oviducal gland produce
different types of egg capsules during the 9-12 months gestation period. After their own egg yolk supply
is used up, the embryos begin feeding on other eggs in the uterus. At about 10 cm the embryos begin
to feed on their smaller unborn siblings as well as eggs during the last 2 or 3 months of the gestation
period the single remaining embryo in each uterus feeds on enlarged egg yolk capsule. – Intra –
uterine canabalism.
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2.2 SMOOTH HOUND SHARK
A common shark especially abundant along the shallow sandy beaches of False Bay and areas of the
southern Cape although they can be found at great depths too. They prefer to swim sluggishly along the
bottom and their diet is mainly composed of
lobster, hermit crabs, and squid. The female
can have up to 25 young which are born alive
after a gestation period of nearly a year.
Many specimens have distinct dark spots on
the upper part of their bodies.
2.3 SPOTTED GULLY SHARK
The overall colour is dark grey with lighter
underbelly and black ‘inkspots’ on its skin.
Numerous rows of teeth are set in a large wide jaw
and arranged in pavement fashion. In summer this
species congregates in shoals in False Bay for
breeding and the females are ovoviparous.
Endemic to South Africa.
2.4 STINGRAYS
There are about 89 species in this family, which occur, in marine, brackish and even freshwater.
Stingrays are bottom dwellers and often lie partially buried under sand or soft mud. This, coupled with
their brown or mottled body covering, makes them totally inconspicuous even in clear water.
2.5 EAGLERAY
This is a brown ray with large eyes and spiracles on the sides of its
head. The females give birth to 3-7 young after a year’s gestation
period. Although not poisonous to man, the poisonous spines on the
tail can give a painful wound which must be soaked in very hot
water to destroy the toxins.
2.6 GUITARFISHES OR SANDSHARKS
The forward part of the body,
including the head, pointed
snout and large pectoral fins,
is
flattened and shovel- or
wedge-shaped. A row of
small, closely set, dermal
denticles forms a ridge along
the midline of the back. The
mouth and gill slits open
ventrally. The eyes and
spiracles on the top of its head are an indication of this family's bottom-dwelling habits. They prey
mostly on shellfish and during summer, females give birth to a number of live young.
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2.7 CATSHARKS AND SHYSHARKS.
Mottled or striped markings provide
camouflage to these sluggish, bottomliving sharks that are found in both
coastal and deep, oceanic waters.
They are nocturnal and feed on small
fish, octopus and other invertebrates.
2.8 JOSEF’S OR ELEPHANT FISH
These unusual fishes belong to the Chimaeriform fishes once diverse and numerous but now mostly
extinct. It is not known if they share a common
ancestor with the shark, however, like the shark they
have a cartilaginous skeleton, and no rib cage. They
have a single gill slit like bony fishes. The female
deposits only 1-2 brown egg capsules on the seabed
after being internally fertilised by the male.
Question:
Which examples (from the list above) of cartilaginous fish do we have in the aquarium?
_________________________________________________________________________________
________________________________________________________________________________
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3. REEF FISH
Reef fish make up the most spectacular elements of coral reefs around the world. The brilliant range of
colours and patterns is believed to have developed for identification purposes. Many reef fishes are very
territorial and distinct ‘poster-like’ colours are shown by the most aggressive species. Other reasons for
specialised colouration are:
Counter shading
where darker and lighter
pigments appear on the
upper and lower body
respectively.
This camouflages the
fish when seen from
above or below.
Disruptive shading
distracts from the fish as
a whole i.e. the false
black ‘eyespots’ near the
tail (e.g. Butterflyfish)
and
the
eyes
camouflaged by a black
stripe (e.g. Butterflyfish,
Moorish Idol, Angelfish
etc.)
Cryptic colouration
which blends the fish into
the coral on which it lives
(e.g. red hawkfish) or the
substrate such as the
poisonous stonefish.
Warning
colouration
such as that of the red
lionfish
could
warn
predators that the fish is
poisonous and should be
avoided.
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Coral reefs have the most species of fish in the world each adapted to specific foods for which the
mouth, teeth, body shape etc has been developed to maximise their chance of survival. In the next
illustration the different mouth shapes give an indication of some of the feeding habits of fishes. ( also
look at page 8 and compare the mouth shapes to those illustrated on page 8)
Threadfin Butterfly fish.
Coachman or longfin bannerfish.
Widespread from Indo-Pacific to Mossel Bay. Widespread from Indo-west Pacific. Grows
Grows to 20cm.
to 16 cm.
Feeds on small reef invertebrates
Preys on small invertebrates.
Birdfish.
Bluestreak Cleaner Wrasse.
Found in Indian Ocean grows to 28 cm. Common and very active fish found in IndoColour varies with age and sex.
Pacific southwards to Algoa Bay. Feeds on
ectoparasites and mucous of other fish
Feeds on small benthic (bottom dwelling) entering mouths and gill chambers if
invertebrates and uses its long snout to necessary. Parasite-infected fish queue up
for ‘cleaning service’ provided by these
remove prey from crevices
wrasse.
Emperor Angelfish.
Powder-blue surgeonfish.
Found from Sodwana to Indonesia and
Found in Indo-pacific and grows to 40 cm. grows to 23 cm.
Juveniles differ dramatically from adults in
pattern and colouration.
Feeds on seaplants.
Feeds on sponges and other invertebrates.
Picasso triggerfish.
Clown triggerfish.
Found in the Indo-West Pacific area grows
Found in the Indo-West Pacific area grows to to 30 cm.
30 cm.
Omnivorous
Preys on hard shelled invertebrates which it
crushes with its teeth.
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4. PELAGIC FISH
The ocean beyond the littoral zone is divided into two regions
(1) Benthic – all plants and animals that live on or near the bottom
(2) Pelagic – all plants or animals in the ocean that are not associated with the bottom.
Pelagic fish are fish that live in the open seas. Many species of pelagic fish migrate along the coast
and breed in large numbers. Pelagic shoals are the main source of fish caught by trawlers and fish
factories. Snoek, tuna and mackerel along with sardines, anchovies and herrings are commonly found in
the sea around South Africa.
Four species of pelagic fish found in the ‘Open Ocean’ or ‘Predator Exhibit’ at the Two Oceans Aquarium
are:
Cape Yellowtail (also called Albacore, or Amberjack).
Grows up to 50 kg and occurs in large shoals in summer in
False Bay down to Struisbaai. In winter they migrate to
Eastern Cape and KwaZulu Natal following the annual
pilchard migration.
Geelbek (also called Cape Salmon)
Grows up to 25 kg and occurs in large shoals at all
times around the west coast although they migrate
up to KwaZulu Natal in spring for spawning. It is a
very aggressive fish and squid feeder.
Elf (also called Shad)
Can grow up to 12 kg but most usually around 1-2 kgs. An
aggressive fish with razor sharp teeth that spawns in KwaZulu
Natal from September to November.
Maasbanker (also called Horse Mackerel)
A spindle shaped silvery fish that grows up to 70 cm and is heavily
fished around the South African coast. Spawns in late winter and spring
and is preyed upon by seals and dolphins.
Task:
1. Find at least two examples of benthic (bottom dwelling fish) in the aquarium.
_______________________________________________________________________
2. What is the national fish of South Africa?________________________________
5. EELS
Eels are long-bodied, snake-like fishes that are usually scale less and lack pelvic fins. The saying 'as
slippery as an eel' refers to the copious supply of mucus that covers the body and makes them very
difficult to grasp. Eels have many more vertebrae and fewer bones in the face and jaw than do other
fish. These structural features are associated with their habit of hiding in holes and crevices or
burrowing in the sand, but some species are pelagic and swim in the open ocean. Perhaps the bestknown eels are the freshwater eels and the morays.
Breeding
All eels, even the freshwater species, breed in the open ocean. They pass through a prolonged stage
called a leptocephalus larva when they are flat, transparent and glassy, quite unlike the adults. The
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larval stage, can last from a few weeks to a few years depending on the species (which migrates great
distances in the ocean currents).
5.1 MORAYS
The most conspicuous eels of the coral reefs are
the morays, which are sharp-toothed, longmouthed and successful predators. Morays often
have distinctive patterning and colouring. In
KwaZulu-Natal morays and rock lobsters often
share a hole. If an octopus feels along the ledges in search of a lobster meal the moray darts out and
catches the octopus instead.
Task:
What kind of moray eels do we currently have on exhibit in the aquarium?
_______________________________________________________________________________
6. SEAHORSES
Seahorses are thought to have evolved at least 40 million years ago. They inhabit
shallow seagrass beds in estuaries and warm coastal water.
Feeding
Seahorses feed on small, planktonic organisms that are sucked through their small
mouths.
Breeding
Seahorses mate for life and are highly territorial. The female deposits her eggs
(where they are fertilised) in the male's pouch, the soft tissues of which provide the
eggs with the oxygen and nutrients.
Pregnancy lasts between two and four weeks and during this period the female
seahorse develops a new batch of eggs. As soon as the male seahorse has expelled
his brood, the female will deposit another batch of eggs into his pouch.
Did you Know?
In the aquarium the temperature for the Knysna seahorse display is kept at 150 C to
prevent them from breeding.
We are not allowed to release the Knysna seahorses as the main threat to them
currently is habitat destruction.
7. SUNFISH
They are found in all, except the polar, oceans. The skin is thick and
tough with small rough denticles, similar to a shark's skin. Although
sunfishes lack a swim bladder, the fat stored in their tissues makes
them light and buoyant.
They have four gill arches and a single round gill opening on the side of
the body at the base of the pectoral fins.
The sunfishes have large mammal-like eyes and seem to rely on their
eyesight for finding food and avoiding objects.
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Feeding
The sunfish sucks jellyfish, salps and comb jellies (on which it feeds) into its small round mouth and
then crushes them, using a parrot-like beak comprised of fused teeth.
Breeding
The sunfish is the most fecund( fertile) of all fishes, producing nearly 300 million eggs that are shed into
the sea during spawning.
CONSERVATION THROUGH RESEARCH AND OBSERVATION
It is almost impossible to observe an animal throughout its life. Many fish are broadcast spawners
shedding their eggs into the vast ocean and others have microscopic larval stages. Obviously it is
equally difficult to find the same adults again and again. In the case of whales, helicopters are used to
track individuals due to their distinctive markings but how could you distinguish between two yellowtails
or two sea urchins?
There are a few methods that have been used and they are described here:
1. Tagging
There are three groups of animals that have been extensively tagged in South Africa either because
they are easy to tag or because of their extensive exploitation and importance to the fishing
industry. They are fish, rock lobster and molluscs.
Tags have to be attached firmly, and survive moulting in the case of rock lobsters, to a suitable
surface and the glue must stick underwater.
The animal has to be recaptured to obtain a result and this is done by relying on the fishing
industry, and the public. Not only do large numbers of animals need to be tagged to ensure some
results (which is very costly), but also more education is needed to get total cooperation from all
sectors.

Fish
The Oceanographic Research Institute (ORI) encourages all angers to participate in their
nationwide Tagging Programme. This involves anglers tagging and releasing their catches. All
participating anglers receive feedback on the statistics they submit and a computerised report if
their fish is recaught.
 Rock lobster
As they grow in spurts just after moulting and before the new shell has hardened, large numbers
have to be tagged before they moult. A long plastic tag with a hook on the end is inserted
between the thin joints of the shell and embedded in the muscle of the abdomen so that it is
retained when the animal moults.
Researchers rely on the rock lobster industry to return all tagged animals and provide reward
incentives. Over 2000 rock lobsters are trapped and tagged annually. The recapture rate is high
enough to provide information on growth rates for management of that stock.
 Molluscs
The most successful results are obtained from animals with shells on which to attach tags and
those like limpets and abalone, which are slow moving and return to their home scars, can be
found again and again. Squid have also been tagged with a ‘spaghetti tag’ embedded in the
muscle.
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How the Aquarium assists with research and tagging process:
Both sharks recently released have been tagged with internal acoustic tags. After anaesthetizing the sharks, the
vet made a short incision (3-5cm) in each shark’s belly, inserted the tag into the abdominal cavity & sutured the
cut. The tag itself is slightly shorter than a white board marker, about the same diameter and has a battery life
of 10 years! These tags are made of a biologically inert material, meaning that it will not harm the shark in any
way; it will stay inside the shark’s body for the rest of its life.
The tag transmits a signature signal that is logged each time the animal passes by a specialized “listening”
station. There are an array of these stations along the South African coastline -this means that we should get
near-shore migration data on each shark for the next 10 years, helping scientists to track their movement,
leading to better understanding of ragged-tooth shark migration, behaviour and population dynamics.
Here's an article Stuart from FLOW wrote for South African Tourism on the shark release, with a 3min video
highlights package of the best bits from the two separate videos: http://blog.southafrica.net/blog/entry/doinginvaluable-work-for-shark-conservation or you can download the Youtube video of Kays release.
2. Aquaria or aquaculture farms
Useful information can be provided from these sources but it needs to be compared to the
natural environment. Only selected species can be grown successfully in captivity in sufficient
numbers such as mussels and oysters. Rock lobsters have a complex and lengthy life cycle as
larvae and this has meant that it is not yet viable to farm these animals despite the obvious
rewards.
Direct observations in aquaria have provided the following interesting facts:
Anemones have been known to live for 100 years in aquaria.
Seahorses born at the Two Oceans Aquarium have grown from 1cm to about 2cm in a single
month.
Mussels are successfully ‘farmed’ by aquaculture – and the black mussel can grow to 6cm in
length in about 6 months reaching 9cm in a year.
Abalone (perlemoen) grows slowly once the larvae settles after 3-6 days. After 5 months in
aquaculture they are only 5mm, after 5 years about 8cm and at 13 years reach 11+cm, which is
the legal size for harvesting. Note that shells of 18cm are about 30 years old!
Octopuses are short lived and die after about a year when their eggs are hatched.
Tropical fish have been bred for many years and a great deal of information has been amassed
about them.
Did you know:
Fertilised kob and yellowtail eggs removed from the I & J Predator exhibit has
been cultured in the Seapoint research aquarium to assist with establishing
aquaculture of these species.
3. Growth rings
Several methods have been
explored using the idea of growth
rings, much like those in a tree
trunk. The principle is that certain
substances are laid down at
different rates under different
conditions experienced seasonally,
monthly or daily – which create
alternating thick and thin layers
seen as rings.
Remarkable results have been
obtained from two groups of
animals – fishes and corals.
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Fish otoliths
Otoliths are the ear bones of fishes. These bones move in a pocket of sensory cells which record
their position and give the fish information about balance, determine its orientation and
speed of turning. Otoliths are distinctive for different species of fish and have summer and
winter growth zones laid down each year, which are best seen when a thin section is taken from
the otolith and polished.
Some fishes lay down two rings a year so the zones need to be verified against fishes of known
ages.
A chemical, tetracycline is injected into a fish to stain the current ring on the otolith. So, if the
otolith is collected a year or two later, the number of rings laid down since the tetracycline
staining can be counted.
Information from otoliths has been used extensively to age fish and even those otoliths
recovered from predators can provide an insight into the species and age of their prey. Obviously
the big disadvantage is that only a dead fish can provide this information!
Corals
Stony coral skeletons record not only annual growth rates, but also monthly and daily rates. This
is because the calcium deposited is affected by temperature, tides and sunlight.
The living coral houses micro-algae in its flesh, which photosynthesises, provides food and
assists in the deposition of calcium during light hours.
4. Year Group Analysis
This method can be used where the animals occur in fairly dense established populations –
especially useful for an animal like the sea urchins is that it is difficult to label! It gives the best
results in animals with distinct spawning times, preferably once a year.
Either - ALL the animals in a FIXED AREA are measured or a FIXED number of animals are
measured. This needs to be repeated at intervals during the year.
The population shows distinct size groups called cohorts, which correspond to larval settlements.
Scientists need to determine what these peaks correspond to – are they annual, biannual or even
monthly peaks. The gonads can be examined by dissection through the year to determine when
the animals spawn. When possible the peaks can be correlated with results from tagging.
The population can also be measured throughout the year to see how the cohorts grow and how
long it takes for cohort 1 to reach the original size of cohort 2 for example.
CONSERVATION VERSUS ECONOMIC FISHING INDUSTRIES
1. OVERVIEW
Over the last century the fishing industry has undergone major changes. Before the early 1900’s no
large-scale fishing existed worldwide however this is not the case today, with fishing fleets roaming the
oceans and removing huge quantities of fish.
In South Africa several factors have to be considered when considering how to sustain our valuable fish
stocks.
2001 Government announces tough new angling limits1. The measures will follow the recent
declaration of a fishing ‘state of emergency’ by Environment Minister Valli Moosa.
Similar measures are being laid down by the United Kingdom and the European Union. Several popular
species have been pushed to the brink of collapse because of the pressure of too many anglers catching
too many fish.
1
This article appeared in March 2001 by Bruce Mann and Independent Newspapers and highlights the current
thinking on fishing.
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Full details of the new line-fish conservation measures have not been announced yet, but officials have
published a list of at least 20 key species, which are considered to be dangerously overexploited or
seriously threatened.
Yet fish harvesting by humans this century has reached alarming, unsustainable levels.
As recently as the 1930’s the total world catch of fish and shellfish was less than 20 million tons a year.
But by 1970, this catch climbed to 70 million tons because of human population growth and improved
fishing technology, such as echo sounders to locate shoals, and more sophisticated freezing techniques.
And locally, fishing competitions have increased the pressure.
It is inevitable that there would be protests when the new regulations are announced. But if dwindling
fish stocks are to be protected for present and future generations, the only options are either to restrict
the number of fishermen or to limit their catches.
It is believed that recreational or ‘sport’ fishermen will still be able to enjoy their sport.
According to the DEAT (Department of Environmental Affairs and Tourism) there are now about 3 000
commercial fishing boats, more than 3 500 recreational ski boats, 400 000 shore anglers and an
unknown number of subsistence fishermen - all chasing a limited pool of about 200 fish species.
The 2800 commercial licences are likely to be cut by more than two thirds to 450 traditional line-fish
vessels, 130 hake hand-line boats and 200 tuna vessels.
Recreational bag limits for some fish could also be cut from five fish a day to just one or two a day,
while in some cases (e.g. dusky kob) a night-time ban on recreational fishing has also been recommended.
Limited Users
On the basis that open access to all is not an option, different controls are appropriate means of limiting
catches and methods of control need to be tailor-made for each stock.
When rights to fish are allocated, issues such as transferability of rights, length of time of these rights,
payments for the rights and methods used to allocate the rights fairly are all critical. Rules and
regulations regarding the capture of fish are promulgated under the Living Marine Resources Act 1998.
Economic Efficiency
Any system that is put in place must be economically efficient as the fishing industry provides
employment and a means of survival for many people and yet the sustainability of the fish resources
must not be put in jeopardy.
At present the government has not agreed with the European Union which has requested that South
Africa grant fishing rights to EU trawlers within her territorial waters. As studies in Namibia have shown
that foreign fishing vessels do not adhere to a quota system and it is very difficult to monitor their
movements.
How do Marine Reserves benefit Marine Life?







Protects them from urban development and human pressures and provides shelter for threatened
species.
Population densities of larger species that are normally exploited by fishermen are enhanced.
Provides breeding refuge from exploitation and better balance of marine ecology.
Protects habitat and helps recovery of damaged areas.
Easier to police than other management methods such as bag and size limits and closed seasons.
Some species need extra protection when spawning.
Protects from pollution.
How do Marine Reserves benefit humans?




Creates recreational facilities and commercial ventures.
Enables observation and study.
Valuable tourist asset for the eco-tourist, providing an opportunity of seeing endemic species in
their natural habitat.
Job creation for tribal people living on the land and fishermen can use their knowledge to educate
visitors.
Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH
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

Enhance certain species in adjacent areas e.g. Galjoen at de Hoop nature reserve.
Act as seeding ground for adjacent exploited areas.
Conclusion
Heavy fines or penalties should be implemented for exploitation of all forms of marine life, and also
beach vehicles that cause damage to sand dunes and sand dwelling plants and animals.
Community involvement will promote job creation and general upliftment of their everyday life e.g. curio
shops etc. Without Marine Reserves, the country could end up with a devastated coastline and nothing
for future generations to learn from or to observe.
2. STATUS OF CERTAIN FISH STOCKS IN 2001
1.
DUSKY KOB
Status: Collapsed.
Recommendation: Increase size limit from 40 cm to 60 cm; reduce
daily bag limit from five fish to one; ban recreational night fishing;
reduce commercial effort by 70%.
2. SQUARETAIL KOB
Status: Collapsed.
Recommendation Increase size limit from 35 cm to 40 cm, bag
limit unchanged pending further research; reduce commercial effort
by 70%.
3. GEELBEK
Status: Collapsed.
Recommendation: Reduce daily bag limit from 10 fish to two; ban
recreational night fishing; reduce commercial catch effort by 50%.
4. SEVENTY-FOUR
Status: Collapsed.
Recommendation: Maintain current fishing ban for at least 10
years.
5. SLINGER
Status: Collapsed.
Recommendation: Reduce commercial effort by 50%.
6. RED STEENBRASS
Status: Collapsed.
Recommendation: Increase Size limit from 40 cm to 60 crn;
reduce bag limit from two to one; reintroduce a closed season from
September 1 to November 30.
7. YELLOWBELLY ROCK COD
Status: Collapsed.
Recommendation: Reduce bag limit from five to one; and possibly
increase size from 40 cm-60 cm.
8. CATFACE ROCK COD
Status: Collapsed.
Recommendation: Possibly increase size limit from 40 cm to 50 cm
and extend current bag limit of five fish per day to include
commercials.
9. SCOTSMAN
Status: Collapsed.
Recommendation: Increase size limit from 30 cm to 40 cm; reduce
bag limit from five fish to one.
10. ENGLISHMAN
Status: Overexploited.
Recommendation; Reduce commercial effort by at least 50%;
reduce recreational daily Bag limit from five fish to one and introduce
a minimum size limit of 40 cm.
11. POENSKOP
Status: Collapsed.
Recommendation: Reduce bag limit from two fish to one for
commercials and recreationals.
12. STREPIE
Status: Under exploited.
Recommendation: Move strepie from ‘bait list’ to ‘exploitable list’
and introduce a daily bag limit of 10 fish as a precautionary measure
13. ELF (SHAD)
Status: Overexploited.
Recommendation: Reduce daily bag limit from five fish to four;
reduce closed season by one month; consider listing it as a
recreational fish only, with concessions to some commercial fishers.
14. KING MACKEREL
Status: Overexploited.
Recommendation: Maintain current restrictions pending further
control measures in Mozambique.
15. QUEEN MACKEREL
Status: Optimally exploited.
Two Oceans Aquarium Recommendation:
Volunteer Manual – MODULE
-- FISH
Page 28
Maintain5current
restrictions pending further
control measures in Mozambique.
REFERENCES
Bond, C.E. 1979. Biology of Fishes. London: Saunders College Publishing.
Bruton, M.N. 1995. Questions & Answers: Sea Fishes of Southern Africa. Cape Town: Struik.
Lagler, K.F., Bardach, J.E. Miller, R.R. & Passino, D.R.M.. 1985. Ichthyology. London: Wiley.
Paxton, J.R. & Eschmeyer, W.N. (eds). 1994. Encyclopedia of Fishes. Sydney: University of New
South Wales Press.
Skelton, P.H. 1993. A Complete Guide to the Freshwater Fishes of Southern Africa. Halfway House:
Southern Book Publishers.
Smith, M.M. & Heemstra, P.C. 1988. Smiths' Sea Fishes. Halfway House: Southern Book
Publishers.
Van der Elst, R.P. 1988. A Guide to the Common Sea Fishes of Southern Africa. Cape Town:
Struik.
Van der Elst, R.P. & Denis King 2000. Everyone’s Guide to Sea Fishes of Southern Africa. Cape
Town: Struik.
Norman, J. R. A History of fishes. Ernest Benn Limited, London
Steven Hall, Your Healthy Garden Pond. A supplement to Essential Water Garden. Aceville
Publications Ltd, Britain.
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