Tuesday 6 August 2013


In the same way as crops and livestock which are cultivated or raised on land, fishes can be reared for meat, oil and bone and fish meals. The practice of rearing fish meals. The practice of rearing fish in specially designated areas of land and water is referred to as fish farming (or fish culture). This practice requires a knowledge of the different species of fish, their growth requirements, and the conditions under which an optimal production of fishes can occur.
As a source of animal protein for man, fish farming is an important aspect of Agriculture. It is also important to the nation as:
(i)                 An avenue for providing employment;
(ii)               A source of foreign exchange earnings through fish exportation; and
(iii)             A source of vitamin-rich-oil, calcium and phosphorous (in the form of bone meal) and fish meal for livestock.
It is important, therefore, to learn about the different types of fish farming that can be practiced in Nigeria. It is equally important to learn and acquire some skills in site selection, establishment and maintenance of fish farms. All these points, including the existing laws regulations on fishing, will be the focus of this chapter.
At the end of this chapter, you should be able to:
(1)   Define fish farming and explain its importance;
(2)   List and describe the various types of fish farming;
(3)   State the conditions necessary for siting a fish pond;
(4)   Establish and maintain a fish pond or an aquarium; and
(5)   State the basic laws and regulations on fishing.
The practice of fish farming developed out of a human desire to control, with ease, the amount and availability of fish at a given period in time. Depending on the environment under which fish production is desired, several approaches can be adopted. Some of these approaches include ranch, pond, and cage cultures.
This is similar to ranching of cattle on the range; but in this case fish are produced within an expanse of natural water. Fish ranching involves the fencing of bodies of water such as the coastal lagoons, streams, and rivers, to retain and restrict the movement of fishes contained there. The fence serves to restrict the movement of fish within the encashment (pen) area thus promoting efficient utilization of energy foods for body building and production.
In situations of high tides, fish from the open sea are washed into the pens and become retained within the fenced areas as the tides recede. The fisherman is thus able to harvest these fishes in addition to previous inhabitants of the ranch.
Little or no supplemental feeding is required in fish ranching, while water is naturally supplied all-year round from the rest of the body of water. Fencing is the major expenditure incurred in fish ranching, though the cost of preventing poaching (stealing) often adds to the production cost. How would you prevent poaching on a fish ranch?
These are bodies of water which are naturally existing or are man-made for the purpose of rearing fishes. Fish-pond farming involves the selection of a suitable location, excavation of soil to create a water reservoir, continuous provision of suitable water, stocking, and maintenance of the pond to ensure optimum fish production. Pond culture provides for the effective control of breeding, feeding, poaching, and harvesting. This is because ponds have limited areas that can be easily managed.
The household aquarium of beautiful fish species is an example of a portable mini-fish pond. Can you list some privately owned fish ponds in your locality?
The productivity of a fish pond is usually higher than that of a ranch of similar area (size) because supplemental feeding, selected species combination, and good quality water supply can be maintained in ponds.
Cage Culture
This involves the rearing of fishes in specially constructed cages which are suspended in a body of shallow water such as lagoons, streams and rivers. This system capitalizes on the fact that if given water in which to swim and breath, and adequate feeding, fish would grow rapidly. That is, like birds raised in battery cages, fish in cages have restricted movement and adequate feeding which enables them to utilize nutrients efficiently for growth and production.
The cages can be made of palm fronds, bamboo, synthetic plastic or any other suitable material. They are usually suspended in water, stocked with desired fish species, and maintained till the fishes reach market size. In this way, the cage culture ensures effective protection of the farmer’s fishes and easy harvesting. It also ensures the regular supply of quality water to the fishes. Although the initial costs of cage production or procurement could be high, the returns on investment are however, very high. The profit margin in cage culture is much higher than in ranching or ponds.
A less popular type of fish farm which is sometimes found in the rice-producing areas of Nigeria is the integrated rice-fish farms. The rice and fish farm entails the stocking of rice paddies/fields (which are usually flooded) with fast growing fish species which are tolerant to low oxygen levels – e.g. Clarias spp or catfishes. Fish thus stocked are harvested with hand nets when the water is drained from the paddy in preparation for rice harvesting.
In the selection of a site for fish farming, certain environmental factors are considered.
These are;
(a)    Quantity and quality of water supply;
(b)   Type of soil;
(c)    Type and density of vegetation; and
(d)   Topography and ground elevation.
Water Supply. Water supply is an important factor in selecting a site for fish farming. This is because fish depend on water for all their needs, that is, to breathe, eat, grow, and reproduce. Thus, water must be available at all times and in good supply.
Water comes from many sources, e.g. rainfall, springs, rivers, the sea, and boreholes. Whatever the source of the water, it must be pollution and contaminant-free to support fish culture. A desirable water source is that which has high plankton population since most culturable fish species are planktivorous (i.e. feed on planktons).
Type of soil: The best   soil for a fish farm is one that contains a lot of clay. This is because the clay holds water well, it serves as a good diking material, and allows little water infiltration. Clayey soils also provide a suitable substrate for algal (planktonic) growth which most fishes feed on.
Type and Density of Vegetation: Sparse vegetation is normally preferred to densely forested areas because of the cost of site clearing. In addition, the amount of stumps and roots found in sparse vegetation is lower and can be completely removed; this becomes necessary to prevent decomposition which may reduce available oxygen and possibly change the acidity of the aquaculture to the detriment of growing fishes.
Topography and ground elevation: topography refers to the run of the land. For fish farming, a topography that allows the farmer to fill and drain the farm with ease is preferred. A gentle slope is most ideal for it allows for less excavation work in constructing the ponds. A survey of the site will indicate the elevation and the ways of ensuring the entry and exit of water to the farm.
Some of the culturable species of fishes in Nigeria are as follows;
1.      Clarias spp. (aro – Yoruba)
2.      Cbrysicbthys nigrodigitatus (Obokun)
3.      Gymnarchus niloticus (eja osan)
4.      Tilapia Sp. (epiya)
5.      Lates nilotica (giwa ruwan)
6.      Gyprinus carpio (Common carps)
7.      Heterotis niloticus
Some of these species of fish, e.g. Tilapia, are planktivorous and generally fast growing while others e.g. Gymnarchus niloticus are essentially predatory. Thus, for the purpose of rearing in fish farms, a combination of planktivores and predators is maintained to reduce supplemental feed supply and achieve a bigger Tilapia harvest. A stocking ratio of ten planktivorus to one predator is considered adequate for optimum production of both species in captivity.
The combination of culturable species on a fish farm is however, based on
(a)    Quickness of growth,
(b)   Shortness of the food chain,
(c)    Resistance to diseases,
(d)   Acceptance of available supplemental feeds,
(e)    Ease of breeding in captivity, and
(f)    Acceptance by consumers, that is, in terms of meat quality, taste, etc.
Establishment and maintenance of fish farms
The site available to a farmer often determines the type of fish farm to establish, for instance, farmers located around the coastal lagoons or along streams and river-banks usually exploit the natural water supply by establishing ranches or cage cultures. On the other hand, farmers located away from such natural water sources are able to produce fish only in artificially created ponds. Thus the type of fish farm to establish is dictated by the available water source.
Also, the species of fish a farmer can rear is determined by the quality of water available. This is because certain fish species are capable of growth in salty waters only while others will only thrive in fresh-water (e.g. heterotis niloticus, Clarias Lazera). There are however, compromise species such as Tilapia, which are capable of surviving in both salt and freshwaters, including brackish waters. In other words, the salinity of available water dictates the types of fish species to rear in a fish farm.
The establishment of a fish ranch is probably the easiest among the three types of fish farming. This is because it only involves the use of wooden poles or bamboo and mesh plant materials or nets. The poles, usually about 2 metres in length, are spaced and forced down into the riverbed or shore bottom to demarcate the area of the farm. Mesh made of plant materials like palm leaves or net are then strung from pole to pole (to about I metrehigh on the poles),to form the enclosure (pen) which often times substends the river bank or shore.  
Where specific types of fish are not the production goal, the native fish fauna of the ranch may be allowed to breed and grow to harvest. If the converse is the case, the ranch is first depleted of its naïve fauna before the desired fish species are introduced (stocked); in which case, the number stocked must equal the amount recommended for the size of the ranch (i.e. the stocking capacity).
The subsequent maintenance of the ranch would involve provision of supplemental feeds and reinforcement of the fence to preven loss of stock or invasion of the ranch by predatory species from the surrounding waters. Aeration of the ranch is achieved by the movement of the surrounding water (in which oxygen dissolution continues undisturbed) in and out of the ranch. In this case, ‘spent’ water from the ranch is constantly replaced with oxygenated water of the surrounding waters.
The desire for easy and efficient harvesting of ranches has often led to the establishment of practical sized ranches. These are easily harvested at will using such tools as fish traps, drag nets, and cast nets. One major advantage of fish ranching is the production of fish and fingerlings on the same farm. Thus at harvesting mature fishes are selectively removed while the fingerlings serve to re-stock the ranch.
Cage culture and management
For cage culture, natural water sources like the lagoons, streams, and rivers are usually used. Cages of about 2 metre x 1 metre x 1 metre are constructed using suitable material such as bamboo. These cages are fitted with floats on the top-sides and suspended and anchored in water about three quarters way up. An opening is usually made at the centre of the top through which fish are stocked, and fed regularly (i.e. twice daily).
The flow of the water source in addition to the 0.25 metres space left on top of the cage enables adequate replacement and aeration of the cage water. Regular brushing of the cage sides is also carried out to prevent clogging by algae (plankton), which may reduce the movement of water in and out of the cage.
The species of fish encaged are usually surface feeders and fast growers (e.g. Tilapia, Carps). The stocking rate is determined by the cage size, but ranges from 200-300 fingerlings for the 2 x 1 x 1m cage. The restriction created by the cage, and the high quality feed (e.g. fish pellets) provided in cage cultures enables the caged fish to grow rapidly and make them ready for market within six months of stocking.
Harvesting is effected by lifting the cages out of the water and collecting the fishes. Unlike the ranch, only mature fish is harvestable in the cage culture; fingerlings and eggs produced by the stocked fishes usually get lost in the surrounding water through the tiny spaces left on the sides of the cage for water movement.
In comparative terms, the cost of cage construction and feed supply is much higher than that of fence construction and management in ranches. The productive ability of cage culture is however, higher than that of reaches. Cages are also amenable to movement from one spot to another with the stock they contain.
Establishment and maintenance of fish ponds
In establishing a fish pond, the factors considered in site selection must be taken into account. The farmer also takes into cognizance the type and size of a pond he can afford, and manage, and which meets his needs completely.
Preceding the construction of the pond, a survey of the land is carried out to determine the slope and thus decide the location of the pond’s main wall (normally located where the slope is greatest and marks the deepest part of the pond). A site with a slope of 2 – 5% is ideal for a fish pond. Next, the wall locations are marked out on the site and excavation work commences.
The depth of the pond depends upon the purpose and the growth of the fish. For instance, a nursery pond for fry is usually shallow (about 0.5m deep) while a production pond for adult fish is usually between 1.5-2 metres deep. Ponds should not be too deep, so as to allow adequate light penetration for plankton growth, and for easy harvesting.
The walls of the pond are then constructed so that their height is at least 30cm – 50cm higher than the water level to be maintained. Also, to make room for the ‘settling’ of the wall after construction, a 10% allowance is further given, so that a pond that is to contain 1.2m of water should have 1.2m + 0.3m + 0.15m (i.e. 10% of 1.5m) as a wall height or 1.65metres. the walls (also called dam dikes, levees or bunds) hold water within the pond; as such they must be made impervious (water-tight) to prevent leakage, and strong enough to withstand the pressure of the water inside the pond.
The drainage system is then established, using bamboo or plastic piping through the main wall of the pond. The pipe is located 30cm from the base of the wall; the end inside the pond is covered with a screen to prevent the escape of pond fish while the outer end is plugged with clay or wood which can be easily removed when the need to drain arises.
The inlet pipe, also of bamboo, plastic or other suitable material should be placed above the water level so that incoming water drops into the pond. This break in water flow enables the water to pick up (dissolve) more oxygen from the air.
If the site had a clayey soil of hard pan, it may be unnecessary to artificially seal the bottom of the pond and walls. However, where the bottom is sandy or gravelly, it should be made water-proof by lining with polythene sheeting or rubber wedged down with some soil.
On completion of the pond construction, it is then conditioned by placing a layer of lime (usually hydrated (builders) lime at the rate of 114kg/ha) at the bottom, about 2 weeks before the pond is filled with water. The lime helps fertilizers to be effective in the pond, and it controls the acid in the soil which may harm fish. After water filling, the pond is left to settle for a few days before it is tested for quality. This implies that the pond water is tested for temperature, oxygen content, pH, hardness, and alkalinity.
For a productive pond, the water temperature should usually range between 20o and 35oC, because at a higher temperature, the fish will not feed and will move slowly, resulting in poor growth.
Fish grow better between a pH of 6.5 and 9.0 and as such, the water ph should be maintained within this range and possibly go through liming. Also, like other living things, fish require an adequate oxygen supply for respiration. This can be maintained in pond water by stirring the water occasionally with a paddle or bubbling air into it artificially (i.e. aeration) or replenishing the water with fresh water.
Once the optimum hardness (of between 50 – 300 parts per million of dissolved salts such as calcium and magnesium) and alkalinity (of between 50-200ppm of dissolved carbonates and bicarbonates) is achieved along with the appropriate pH, the pond could then be stocked. Usually, 10,000 – 20,000 carps per hectare or about 20,000 tilapia per hectare is considered adequate in monoculture of these species.
Subsequent maintenance of the pond would include:
(a)    Daily feeding of the fish with foodstuff such as bread-crumbs, rice bran, fish meal, ground maize, broken rice, soyabean cake, sweet potatoes, groundnut cake, silkworm, pupae, fish pellets, and some animal manures. Occasional fertizers could be effected to promote plankton growth which later becomes a food source to pond fishes. It is important to provide only the amount of feed the fish can consume at the time of feeding because, excessive feeding may be injurious to the fish and leftover feed may or could tie-up pond oxygen through decay oxidation. 5% of the fish body weight should be fed daily for six days a week,
(b)   Checking the pond for leaks,
(c)    Watching fish behavior near the feeding area to determine if there is any stress on them as a result of low oxygenation of pond water, which may then imply need for replenishment,
(d)   Watching for predators such as crabs, eels, strange fish, and snakes,
(e)    Improving the water quality through the addition of lime.
There are two sets of regulations, governing fishing and fishery. These can be classified as
(i)                 International regulations and
(ii)               Local regulations.
For our purpose, it is sufficient to summarize international fishery regulations as those which
(a)    Defines national fishing zones (preserves) as that 100 nautical miles of water sub-stending the  national land mass;
(b)   Declares bodies of water outside this national fishing zone as international fishing areas;
(c)    Forbids nations of the world from mining or polluting international waterways; and
(d)   Forbids the killing of near-extinct aquatic animals such as certain species of whales, seals, etc.
On the local level, the Nigerian government have regulations which
(i)                 Forbids the harvesting of fish by poisoning (e.g. with gammalin 20) or dynamiting (with explosives) both of which pose health hazards to human consumers;
(ii)               Forbids industries and manufacturers from discharging factory waste into streams, or rivers, which serve as a source of water to fish farmers or as a source of drinking water to other communities upstream.
In this chapter, you have learnt that:
1.      The practice of rearing fish in special or artificially created areas of land and water is known as fish farming.
2.      Fish farming is important for the production of fish which is a source of animal protein, vitamin-rich oil, calcium and phosphorus as well as fish meal for livestock.
3.      Three types of fish farming exist in Nigeria, ranching, cage and pond cultures.
4.      Water source and supply, soil type, and topography are some of the factors to be considered in site selection for fish farms.
5.      Combination of culturable species of fish for farms are based on quickness of growth, resistance to disease, ease of breeding in captivity, acceptance by consumers, and feeding habit.
6.      About procedures for the establishment and maintenance of ranch, cage and pond cultures.
7.      Regulations are established which specify national fishing zones, international fishing zones, and forbids use of poisons and dynamites for harvesting fish.

1 comment:

  1. I would like to thank you for the efforts you have put in writing this website. I am hoping the same high-grade site post from you in the upcoming also. Actually your creative writing skills has inspired me to establish aquaculture project.

    Aquaculture Fishing