WEEK TWO
SUBJECT: AGRIC SCIENCE
CLASS: GRADE 8
TERM: SECOND
TOPIC: FISHERY AND FISH
FARMING
MEANING AND
CLASSIFICATION: Fishery is a branch of
agriculture which deals with the methods and general principles pertaining to
the production and management of fishes and some other aquatic animals.
CLASSIFICATION OF FISH: Fishes
are classified by basing them on certain criteria. Such criteria include the
following;
(A) HABITAT: This is
the classification of fishes which is based on their living environment i.e. the type of water in which they
live and grow. Fishes are therefore classified as fresh water fish and salt
water fish.
Fresh Water Fish: This
category of fish lives in a fresh water (salt-free water) environment like
ponds streams, rivers, lakes etc. Examples are mud catfish, tilapia, heterotis,
clarias, alestes, etc.
The Mud Catfish (Clarias
lazera): This is a fresh water variety found inland water streams and ponds.
It is also able to live in slightly salty water. It is usually smaller and
darker than either the sea catfish or the brackish water catfish. It breeds all
year round and fingerlings are easily transported into standing water pools. It
is a natural invader of ponds, living on both water plants and animals of
smaller sizes. It can also be grown in artificial ponds with tilapia and fed
supplementary feeds. Clarias is very popular for eating and is usually smoked
or fried.
Tilapia Spp: There
are many types of these scaly medium sized fishes. The most common examples are
tilapia melanopleum and Tilapia (Oreochromis) lotica. Tilapia melanospleum is
more tolerant to saltiness in water than Tilapia (Oreochromis) nilotica which
lives better in fresh water. Both fishes vary in length from 10 cm to 25 cm.
They produce large quantities of eggs all the year round. Tilapia fishes feed
on algae, phytoplankton, deritus and supplementary feeds. The fingerlings or
young fish usually invade ponds naturally from nearby streams.
Salt Water/Marine
fishes: These types of fish are those that only live in salt
water-oceans and seas. They cannot live in an ordinary fresh water environment.
Examples are bonga fish, croaker, ray, mackerel, sharks, silver fish, sea
catfish etc. They are mostly referred to as pelagic fish.
(a) The Croakers
(Pseudotolitbus Spp): These fish belong to a class of fin-fish found
along the Nigerian coast. They are called fin-fish because they have prominent
fins. Croakers spend the whole day at the bottom of the sea below 20 m deep.
They rise and disperse in the water column during the night. There are many
types of croakers varying in length from 10 cm to 30 cm, but they can grow up
to 120 cm when fully mature. The males and females mature at different sizes
and produce eggs throughout the year. They produce the largest number of eggs
between January and February and April to July Croakers are scaly fishes. The
two most common types are those with a sea blue color and the short croaker,
which is of a silver blue color. Croakers are caught by trawl netting drawn by
big ships. They are used for food.
(b)The Silver or Cutlass Fish
(Trichiurus lepturus): These are the common inshore fishes and the second
most important group found in the West African coastal waters. The fish can be
as long as 200 cm when fully mature. It is dark, silver grey in color with a
pointed head-end.
It has
very fine scales. Young fish of 12 cm to 30 cm in length are raised near the
coast. The adult fish live in the bottom level of the sea during the day, but
move upward and disperse at night. The male and female fish look alike and
occur in equal proportions in the sea.
(c) The Sea Catfish: This is
found in the deep sea along the shores of Nigeria. It is usually found off the
mouth of the Escravos River and the Niger delta at various depths of 10-13 m.
The adult fish can grow to a length of 70 cm and is usually caught by large
nets drawn by ships called trawlers. The fish has light pink skin with a flat
head which is bigger than the body. Other members of the group may grow to
bigger sizes. The sea catfishes produce a small number of eggs varying from
forty-five to ninety. The survival of the fishes is ensured by the excellent protective
ability of the male parent. In the catfishes, the males protect and incubate
the fertilized eggs in their mouths until they are hatched. Usually, as many as
eighteen young fishes of 10 cm in length may be hatched from one mature male.
(B) MORPHOLOGY: This
involves classification based on the type of skeleton possessed by each fish.
In this account, two types are identified. These are:
Bony Fish: This is
the category of fish having bones as a skeleton. Examples are tilapia,
mackerel, catfish, carp, fimbriata, etc.
Cartilaginous Fish: In this
category, fish have cartilage as a skeleton. Examples are sharks, skates, ray,
dogfish, electric fish, sawfish, etc.
OTHER AQUATIC ANIMALS
Shell Fish:
Examples of shell fish are shrimps, crabs, lobsters, prawns, crayfish, oysters,
periwinkles etc.
Shrimps of the Nigerian Coast:
Shrimps
are sea animals which belong to the class known as Crustacean in the animal kingdom.
Like the insects, the crustaceans belong to the large group of animals known as
Arthropoda. All the arthropod's bodies are functionally divided into head,
thorax and abdomen. Their external skeleton is made up of a
cellulose-resembling compound known as chitin. They have jointed appendages and
a highly developed compound eye. The appendages are made up of a series of
short rigid pieces held together at the joints by soft tissues. There are two
main shrimps that are of economic and commercial importance in Nigeria. They
are the pink shrimp (Penaeus duorarum) and the red shrimp (Parapenaeus
longirostris).
The Crab: These
animals also have a large external skeleton which usually look like a large
shield on their backs. The legs or appendages extend from underneath the backs
and may or may not be hairy. There are various types of crabs in Nigeria viz.:
The African Fresh Water Crab:
It has
the scientific name of Sudanonautes africanus. This animal is found in holes
called burrows along muddy banks of fresh-water brooks and streams. It is
brownish in color with prominent eyes. It can usually be found at night.
The Swimming Crab: This is
also dull grey or light brown in color. It is found in the lagoons. It has a
flattened appendage which it uses for swimming. Its burrows are found on the
edge or on the beds of Lagoons.
The Common Mangrove Crab: This is
another land form of crab. The animal digs into the lower soil layers in
mangrove areas. It only comes out at night. Some of these mangrove crabs are
more hairy than others. The hairy mangrove crab lives under the drift at high
tide mark.
The Ghost Crab: It is a
smaller type of crab found on sandy shores at high tide mark. It is a land-form
crab but its burrow must have water in it.
Lobsters: live
in salty or brackish water.
Prawn: Prawn is
a common name for small aquatic crustaceans with an exoskeleton and ten legs
(which is a member of the order decapoda), some of which are can be eaten.
The Crayfish: These
are much larger than shrimps and are found at the beds of rivers. In Oyo State,
a large grey crayfish known by the scientific name of Macrobrachium spp. is
found in the River Osun near Asejire. The body has an external skeleton of
chitin and lime. The head has five segments, the thorax eight segments and the
abdomen, six segments. The crayfish has a pair of jointed appendages on each
body segment. The appendages can be just as long as the body. The body coloration
of the grey crayfish turns red when boiled.
Oysters: Oyster
is a common name for a number of different families of salt-water bihalve
mollusks that live in marine or brackish water habitats.
Periwinkles: Periwinkles
is a species of small edible whelk or sea snail, a marine gastropod mollusc
that has gills and an operculum.
Reptiles:
Examples of reptiles living in water are turtles, crocodiles, alligator etc.
Mammals: Mammals
in the water include hippopotamus, whales, dolphins, seals, etc.
USES OF FISH AND FISH
PRODUCTS:
(i) Fish
and other aquatic products are used as food for human and animal consumption.
(ii)The
skin of fish e.g. cartilaginous fishes is processed into leather for
manufacturing belts, shoes, bags, etc.
(iii)Fish
bones and scales are processed into animal feeds, for manufacturing glues and
fertilizers.
(iv)Some
fishes are good sources of oil which are used as food and for manufacturing
soaps and medicines e.g. cod liver oil.
(v)Oysters
and periwinkles shells are sometimes mixed with cement as a hardener for
building construction and beautification purposes.
(vi)Fishery,
as a science and art, creates employment opportunities for the scientists and
the farmers respectively.
FISHING METHODS AND EQUIPMENT:
(a) Scoop Nets or Fixed
Bag Nets: These are made out of nylon strings closely woven
into netting material and then sewn into bag-like containers of various sizes.
They are mostly used for catching fish in streams, ponds and smaller fish
farms. Some scoop nets are large enough to be drawn by boats.
(b) A line: The
simplest method for catching fish is by the use of a string or rope called a
‘line’ which is tied to a hook with bait at one end. Commonly used baits are
earthworm, small fishes or maggots. This is used by individuals to catch fish
anywhere. The strength of the line as well as the size of the hook and the type
of bait will depend on the type of fishing being done. Small strength twines or
cords with small hooks and baits of earthworm are commonly used when fishing in
a pool, or stream for tilapia or clarias.
(c) Cast nets: These are conical falling nets, with lead
weights attached to them at regular
intervals along the perimeter of the cone. The netting of cast nets is made of fairly
thick synthetic material popularly known as nylon with mesh sizes varying
between 12.7 mm and 50.8 mm. The total length of each net varies from
4.20metres to 7.11 metres with a retrieving line for four metres to ten metres
attached to the apical portion. Cast nets are used to catch fishes of 5cm to
10cm in total length like sardines.
(d) Gillnets: A
gillnet is basically a curtain of nylon netting hanging vertically in the
water. The mesh sizes range from 25.4mm to 127mm. Head and foot ropes pass
through the marginal mesh at each end of a net. Gillnets and drift net are used
for catching fish species like catfish and sardines in shallow and deep water.
(e) Seine Nets: These
are used along beaches in mud flats and other shallow areas at the mouth of
rivers. Usually one net is fixed or closed and the free end is used to surround
a given area. Fish are then trapped within the area enclosed by the net. Seine
nets are useful for fishing in ponds. Small fishes like crayfish and mullets
are usually caught by seine nets.
(f) Bouys: These
are used along with the nets to serve two main functions. They mark the whole
length of gillnet for easy identification especially at night and ward off
other canoes from the fishing zone. The sound bouys located in Lagos lagoons
are made with raffia cane sticks. They look like rectangular crowns. Empty cans
of beer or shell of snails are attached to the crown. As a result of the movement of the water, the
shells knock against each other and make a sound. Sometimes a lantern is
mounted on a floating board and this serves as a buoy. It has the advantage
that it can be sighted at night and the light also attract some fishes. The
floating board can be made of cork.
(g) Purse Seines: These
are larger nets which measure over 1000m in length and 120m in depth and are
used in industrial fishing. Deep sea fishes such as tuna, mackerel and sardines
are caught by purse seines. These nets can only be put in place by a large
mother ship and two small ships. The net has a float line which is held on top
of the water by small floats and a lead line which sinks to the bottom. The purse
seine is used to encircle a shoal of fish and requires the power from the main
ship to bring in the catch.
ASSIGNMENT
OBJECTIVE QUESTIONS:
1.
Which of these methods is NOT good for harvesting fish? The use of A. basket B.
explosives C. hook and line D. net E. spear
2.
Which of these tools is not needed in fishing? A. bait B. cast net C. sickle D.
spear E. trap
3.
The following are bony fishes except A. tilapia B. mackerel C.
catfish D. carp E. shark
4.
The possession of gills by fish enables it to – A. defends itself from their
predators B. feed from micro plankton C. move freely in water. D. takes
dissolved oxygen and remove carbon dioxide. E. takes in water and removed waste
5.
Which of these fishes belong to cartilaginous family? A. Catfish B. Carp C. Dog
fish D. Mackerel E. Tilapia
6. All these are mammals living in water except
A. cat B. hippopotamus C. Dolphins D.
seals E. whales
THEORY QUESTIONS:
1.
What is fishery?
2.
Classify fish with examples.
3.
Mention three other aquatic animals and give two example of each
4.
List three uses of fish and fish products
5.
List seven methods of fishing.
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