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Agricultural Science

Fish Farming

Definition of fish farming

Fish farming (culture) is the act of rearing selected species of fish under scientifically controlled conditions in enclosed bodies of water such as pond, streams, rivers etc. where they feed, grow, breed and are harvested for consumption or for sale.

Terms associated with fish farming

Fingerlings                             –               The newly hatched fish(es)

Fisheries                –               This is the study of fish and fishes

Fish                                         –               This refers to a particular species, regardless of the

Number or quantity

Fishes                     –               This refers to the different species of fish

Pond                                       –               This is artificial body of water where fish (es) can be reared

Gears                                      –               These are equipment used in harvesting fist

Fry                                          –               This refers to young fish (es) or baby fish(es)

School                    –               This is a group of fish (es)

Hatchery                                –               This refers to a unit where fish eggs are incubated and

Hatched artificially into fish

Aquarium                              –               This is an artificially fish pond kept for aesthetic or

Entertainment purposes at home

Aquaculture                          –               This refers to the study and production of fish, shrimps

And other aquatic food organisms.

Importance of fish farming

Fish farming important for the following reasons:

  • T provides fish which serves as a source of food e.g. protein to man and livestock
  • It provides a means of increasing the availability of protein to people at reduced

cost

  • It provide a means of recycling wastes e.g. animal dungs from farms, factories

and sewage disposal system

  • Fish can be processed into fish by products such as fish meal, fish oil, manure

and skin

  • It provides employment and income to many people
  • A better use of land and water in our environment is also ensured through fish

farming

  • It can generate foreign exchange to a nation, especially when fish are exported

to others countries

  • Fish farming is also useful in the area of research work and other educational

purposes

Conditions of factors necessary for siting a fish pond

The factors or conditions necessary for siting a fish pond include:

  • Adequate water supply
  • Soil in the area
  • Vegetation of the area
  • Topography of the area
  • Availability of fast growing fishes
  • Availability of supplementary feedstuff.
  • Adequate water supply: There must be constant supply of water of good quality and quantity. The water can be from streams, lakes, rivers, irrigation canals, springs etc. Good quality water is necessary because it will provide oxygen and food to fish, create a medium for waste discharge and reproduction. The water should not have a bad smell, taste or colour and should not be too muddy and must be free from pollution
  • Soil in the area: Soil in the area must be fertile so as to supply nutrients to the fish. It should be clay because of its ability to hold water which is very important in fish pond construction. Soil with too much sand or gravel is to good and would not retain water
  • Vegetation of the area: Low vegetation especially grasslands are preferred. Woody sites are not suitable because clearing and stumping will greatly increase the cost of setting up the fish pond
  • Topography: The shape of the land should allow for easy draining and filling of pond with water. The water must flow from a place that is higher than the pond so that the water can flow into the pond directly if not, the need for water pumps would arise and this will increase the cost of the project. However, fish pond can be constructed on a flat or level ground but lots of soil have to be removed to create the slope
  • Availability of fast growing fish: fingerlings or baby fish for stocking a fish pond should be the type that can grow fast and mature within a very short time. The use of improved varieties (breeds) in stocking fish pond makes fish farming more profitable
  • Availability of supplementary feedstuff: Supplementary feeding is done to ensure rapid growth of fish and allow high stocking density. Artificial or compounded feeds in from of pellets are used to supplement the natural feed (planktons) the addition of fertilizers also promotes the rapid growth of planktons (natural fish food) in the pond.

Classification of fished

Fishes can be classified into two main groups:

  • Classification based on fish habitat: under this classification, two groups exist:
  • Fresh water fishes: These fishes live in fresh water i.e. the water does not contain salts. Examples of such fresh water include pond, streams, rivers and lakes. Examples of fishes in this group include tilapia, carp, perch, trout, mudfish etc.
  • Salt water fish: These fishes live in water containing salt such as lagoons, seas and oceans. Examples of salt water fishes include salmons, mackerel, shark, tilapia, rays, eels, etc.
  • Classification based on body structure under this classification, two groups also exist:
  • Bony fishes: These fishes possess bony skeletons. Examples include tilapias, mudfish, carps, trout, catfish, salmon, perch, and herring. Majority of these fishes are found in fresh water.
  • Classification fishes: These fishes possess soft bones composed of cartilages. Majority of these fishes are found in salt water and examples include shark, dolphin, dogfish, and rays.

Features of a standard fish pond

The essential features of a standard fish pond (fig. 31.1) include: (i) Dam (ii) Core trench

Fig. 31.1: Top or Aerial view of a fish pond

  • Distribution channel
  • Spill way
  • Monk
  • Boards
  • Screen
  • Dam slope (inner and outer).
  • Dam: This is the large area of the pond that holds water. It ensures the

availability of water in the pond

  • Core trench: This is the excavated portion of the fish pond. It consolidates the

walls with stones and cement

  • Distribution channel: This is the area which helps to introduce water nto the

pond. Water is distributed to all the sections of the pond until it gets to a particular volume. Fertilizers can equally be mixed up with water and distributed together

  • Spill way: This is a passage for water to flow over or around a dam. It is

positioned at one end of the dam. It uses wood or wiremeshed screen

  • Monk: This monk regulates water level automatically in the pond. It helps in the

discharge of water from both the surface and bottom. It has vertical low and horizontal culverts or pipes. They are constructed with concrete

  • Boards: These are structures which regulate the flow of water. They are made

up of desirable wood and also hold water inside the pond. They are fitted at the Centre or middle of slabs at the gates

  • Screens: These structures helps to prevent the entry of undesirable species of

fish into the pond. They also prevent fish movement out of the pond

  • Dam slope (inner and outer): This helps to regulate water movement into and

out of the pond. It also ensures the availability of water in the pond. It is usually constructed at the beginning and end of the pond.

Establishment/construction of a fish pond

The following operations are normally carried out when establishing a fish pond:

  • Site selection: Site selection involves the choice of best site based on necessary

conditions like, a piece of land through which a perennial stream flows. The site should be on a fertile and clay soil to prevent seepage of water. It should have a valley with narrow neck and at a fairly open area

  • Reconnaissance or general survey: Detailed survey of the chosen site should be

carried out, especially by extension workers. Such workers help to determine the height of pond, volume of earth to be used for duke, total water surface area, volume of water in the pond or embankment

  • Clearing and stumping of site: This involves the removal of thrash, cutting of

trees and removal of stumps

  • Construction of dam: Dam is usually constructed across the stream. Material

used in the construction should be of good quality. Clay soil should be used for dam construction because of its ability to hold water

  • Construction of core trench: This involves the removal of the soil or excavation.

It is positioned at right angle to the dam. Such dam should be made with consolidated stones or cement walls

  • Construction of spill way: Spill way is positioned at one end of the dam. Wood

and wire-meshed screen should be sued to construct the spill way

  • Impoundment of pond: This involves the filling of the pond with water by

opening the monk board of the reservoir. This leads to the release of water and flow to fill the pond

  • Liming: This involves the addition of limestone or calcium carbonate powder to

the sides and bottom of the pond to seal pores and prevent water loss. Liming also reduces acidity of the pond water and encourages the growth of planktons (fish food). However, liming is done before filling the pond with water. The lime materials should be left for four weeks in its dry state

  • Pond fertilization: fertilizer encourages the growth of planktons (fish food).

Pond fertilization is done by pouring organic fertilizers such as poultry droppings, cow dung or the use of inorganic ones like N.P.K. or super phosphate. Pond fertilization should be carried out 15 days before stocking pond with water

  • Pond inoculation: This is the introduction of proper plankton’s species into the

pond. This is done by obtaining some water from a plankton rich pond and pour into a newly fertilized pond. When the pond water begins to turn green, this green water indicates the abundance of planktons (natural food of fish). To keep the water green, fertilizer is added into the pond every week

  • Stocking of pond: this is the introduction of the proper baby fish called

fingerlings or fries into the pond. The pond is stocked at the rate of two fingerling per square meter. The fingerlings should not be poured into the pond, rather, the container should be placed gently into the water and the fingerlings allowed to swim into the water pond themselves.

Maintenance of a fish pond

To ensure the continuous availability of fish in a fish pond or maintain high fish yield, it is necessary to ensure:

  • Regular feeding: The fish must be fed twice daily from selected point (s).

supplementary feed in the form of compound feed should be given in sufficient quantity to ensure rapid growth and early maturity of the fish

  • Deweeding: This is the removal of weeds from the pond. It allows the

dissolution of oxygen in water, the penetration of sunlight to the bottom of the pond which will promote the growth of fish food (planktons). It also prevents the build-up of pests and disease

  • Desilting: This is the removal of silt or prevention of silt from entering into the

pond. Desilting makes the water to be clean, promotes easy movement of fish within the water and also prevents pollution of the water

  • Aeration: Aeration enables oxygen to dissolve in water which is required by fish

to dissolve in water which is required by fish for respiration. Fishes usually come to the surface of water due to lack of oxygen in the water. Weeds, excessive organic manure, overstocking etc. prevent proper aeration of the pond

  • Constant supply of water: The pond should always be filled with water and any

leakage repaired

  • Control of predators: Predators like birds and snake should be prevented from

entry into the pond because they could eat up the fish in the pond. This can be done by keeping the pond surrounding clean (e.g. by constant weeding).

  • Prevention of diseases: Diseases should be prevented as this could kill all the

fish in the pond. Adequate feeding, stocking, temperature, manuring, weeding, etc. help to prevent diseases

  • Regular harvesting: Regular harvesting of fish is necessary to prevent over

population, outbreak of diseases and cannibalism. Periodic or total harvesting could be done six months after stocking, using net or by draining of the pond

  • Regular application of fertilizer: This should be done once in a month to

promote the growth of fish food (planktons) in the pond.

Processing and preservation of fish

Harvested fish is either consumed, sold or preserved for future use. Fish processing involves the removal of scales, fins, gut and gills. The remaining part is than cooked or fried for eating. By-products of fish processing include (i) fish meal (ii) fish scales (iii) cod liver oil (iv) fish skin.

Fish can be preserved for future use by any of the following ways:

  • Salting: This is the application of salt on the fish. It prevents the growth of

spoilage organisms

  • Smoking: This is the drying of fish over naked fire. It reduces he moisture

content and increase the taste and flavor of the fish

  • Sun-drying: This involves the drying of fish using heat from the sun. in this

process, fish can only be stored for a short time

  • Freezing: This involves the use of cold storage like refrigerators and deep

freezers to store fish over a very long time

  • Canning: This involves the storage of processed and consumable fish in cans

under special conditions for future consumption e.g. sardine.

Fishing tools or gears

Examples of fishing tools or gears commonly used to harvest fish (es) include (i) cast net (ii)  drag net draw net or sein net (iii) clap net (iv) set net (v) trawler with sein net or fishing trawler (vi) fish traps, gill net, fishing basket, harpoon or spear.

  • Fishing nets

Functions/Uses: Fishing nets are generally used for the harvesting of fish (es) from either ponds, streams, rivers, lakes, oceans or sea

Description: There are various kinds of nets commonly used. Examples include:

  • Scoop net: This is a small net which may be rectangular or cylindrical in shape

with the required or regulated mesh size. It has a wide mouth and a small / long wooden handle. After the pond has been drained, harvesting can be done with a scoop net (fig. 31.2)

  • Gill nets: Gill nets are used to harvest or catch bigger fish (es) in a pond, thus,

leaving the smaller fish (es) until they attain bigger sizes. Gill nets are usually made of 2-3cm mesh size. They are called gill nets because the fish pokes its head through the net mesh and is caught around the gills as it tries to wriggle through the net. The gill nets have lead sinkers (weights) at the bottom rope and floats at the top ropes

  • Seine net: A seine net (fig. 31.3) is capable of collecting all the fishes in the pond

at once because it has smaller mesh size than the gill nets. It is made of heavy fibre to hold the fish. The nets usually have lead sinkers (weights) attached to the bottom ropes. These weights hold the nets at the bottom of the pond so that the fish cannot escape underneath the floats attached to the top ropes to help the net form an enclosure. Seine net is used with trawlers called fishing trawlers

  • Fishing trawlers: This is a large fishing boat in which large nets called seine nets

can be attached. It is used for harvesting large fish (es) in the deep sea or oceans. The net can or is capable of harvesting or catching large quantities of fish (es) at a time for commercial purposes

  • Fishing basket: This is a fishing tool designed like a basket (fig. 31.4). It has a

cylindrical shape with a wide mouth. It has a trigger close to the mouth while at the taper end, holds the food (bait). The bait attracts the fish and when it enters the basket, the trigger is pulled down as the body of the fish touches it and this closes the mouth of the basket. By so doing, the fish cannot come out of the basket as it is being trapped

  • Hook and line: The hook and line is also a fish harvesting tool. It has a long

wooden handle (fig. 31.5), a long line, rope or twine, a float and a hook. The principle used in hook and line fishing is to offer the fish a bait (usually a small piece of fish or earthworm) fixed to a hook at the end of the line or rope. The fish while trying to bite the bait, swallows the hook and thus gets caught.

Other method of harvesting fish include:

  • Trapping: This involves the setting of traps to catch fish. It involves the use of

gears made from ropes or raffia woven into various models of enclosures for capturing fishes. They are set along water courses and any fish that enters the trap would not be able to get out but remains there until it is caught by the fisherman

  • Netting: This involves the use of various types of nets to catch fish. Nets like gill

net, clap net trawl net etc. which have been woven into various sizes and thickness are thrown into water to catch fish

  • Electro-fishing: This involves the use of electricity to catch fish by creating

electric fields in an enclosed area such that current is sent across, killing fishes between poles. It can only be used for total harvesting of fish

  • Draining of ponds: This involve draining of pond water for easy use of net to

catch large fishes

  • Use of ultrasonic: This is an instrument which can make sound in water and

attract fishes so that they can easily be trapped or harvested using other means of harvesting

  • Impaling: This involves the use of spears or harpoons to attack and catch big

fishes.

Basic laws and regulations of fishing

Meaning: Fishery regulation is a set of rules and laws governing the exploitation and other practices of fishery resources, especially in open access water. In other words, fishery regulations are laws made by the government in order to control and protect fish harvesting so that they do not go into extinction and for them (fishes) to be in regular supply from time to time.

Fishery regulations or decree in Nigeria was promulgated in 1971 during General Yakubu Gowon’s regime. The regulations are:

  • Close season: This is a regulation in which no fishing is permitted to take place

for a given period of time. This allows the smaller fishes to grow and mature

  • Catch quota: This is a form of control in which a fisherman is allowed to catch a

specific quantity of fish or regulating the number of fisherman by issuing them fishing permits or licenses at a specific amount

  • Mesh size regulation: This involves the use of a particular mesh or net size such

that only the matured fishes are caught, thus protecting the young ones

  • Regular stocking: This involves the addition of compactible species of fish to

increase the population of fishes in water

  • Population control: This involves the use of other fish types like clarias (catfish)

to eat up tilapia or early harvesting to prevent over population

  • Prevention of vessels: No vessels (except canoes) shall fish within the first two

nautical miles of the water of the Nigerian continental shelf

  • Ban on the use of poisonous materials: The use of noxious or poisonous matter

is prohibited because it often results in the death of both the mature and the young fishes

  • Ban on the use of poisonous materials: The use of noxious or poisonous matter

is prohibited because it also result in the death of both matured and the young ones

  • Landing tax: Landing tax should be introduced such that total catch and sizes of

fish should be taxed at the site of landing

  • Allocation of fish areas: Fishing areas are allocated to individual fisherman so as

to curb indiscriminate interference within large fishing areas

  • Restriction on breeding section: The breeding section of water should be

identified so as to restrict fishing in the section

  • Ban on discharge of pollutants or toxic substance:Pollution or toxic materials

should not be discharge into the Nigerian waters

Ways of making fishery regulations effective in Nigeria

There are several ways in which fishery regulation can be made effective in Nigeria these are:

  • Use of local or native languages: The fishery regulations should be written and

made available in local or native languages

  • Simple presentation to fisherman: The regulations should be presented to the

fishing community or fisherman in very simple ways

  • Wide publicity to create awareness: The regulations should be given wide

publicity, using radio, television, posters, leaflets/handbills in order to bring such to the awareness of the people

  • Use of law enforcement agents: Appropriate law enforcement agents should be

used to enforce the regulations

  • Revocation of licences: There should be revocation or withdrawal of licences of

defaulting fisherman

  • Prosecution of defaulters: There should be prosecution of defaulting fishermen.

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