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Fish Farming: How to Produce and Manage a Fishery in the Tropics

how-to-produce-and-manage-a-fishery-in-the-tropics

If you are reading this article you are probably looking to start your own fishery. This article will discuss basic things involved in starting fish production but you still need to get specialised advice regarding your unique soil type and other factors affecting your fishery.

Most fish farmers start small by growing a few fish for fun and expand to large-scale commercial operations only after they gain the necessary skills and experience.

Commercial fish farming is a time-consuming, expensive, high-risk business that requires careful planning, a good understanding of fish biology, and sound business management skills. A careful study of economic considerations, especially product demand, financing, production costs, and marketing should be conducted before investing in a commercial fish farm. See the table below for the costs of running a fishery.

Typical Cost of Running a Fish Farm

Capital CostsOperating Costs

Land

Fish

Pond Construction

Feed

Buildings

Electricity

Hauling Trucks

Fuel

Water Supply

Labour

Plumbing and Pipes

Transportation

Hauling Tanks

Maintenance

Aerators

Chemicals

Oxygen meter

Drugs

Nets and Seines

Telephone

Waders and boots

Taxes

Feeding Equipment

Interest

Tractors and Mowers

Insurance

Growing Your Own Fingerlings

Many different hormonal preparations have been successfully used to induce spawning in African catfish. Some of these include HCG, DOCA, Carp Pituitary Suspension, Progestagen, Pimozide, and LHRha. However, the catfish farming community in Africa is now using mainly a homoplastic pituitary gland suspension to induce spawning.

This technique has been found to be highly dependable and, in comparison to synthetic hormone analogs, it is cheap and practical. This is of particular importance in African countries where sophisticated chemicals are often expensive and difficult, if not impossible, to obtain.

The whole pituitaries are removed from sexually mature adult catfish during the spawning season and are either used immediately or are stored in absolute ethanol or acetone, or stored dry after acetone or alcohol impregnation for up to 18 months with no loss of efficacy.

Pituitaries can be taken from males or females. The pituitaries are homogenised in sterile water or pure rainwater and injected into the female. The dose is calculated on a 1.5:1 (donor: recipient weight basis).

Females with suitably developed eggs can usually be stripped 12 hours after receiving a single dose at a temperature of 28oC, or 20 hours at a temperature of 22oC. At this stage the eggs have been hydrated and have gone through the process of ovulation.

The ovaries at this stage can occupy up to 70% of the abdominal cavity. Broodstock females usually vary between 1 and 2 kg in weight. Owing to high levels of aggression, the effects of which can be quite severe, broodstock females after injection
are usually separated from each other in the holding tanks by way of sturdy screens.

A simple and completely reliable method of testing the readiness of the eggs for fertilisation is by holding the females in a headup vertical position. If the eggs begin to run freely from the genital pore they are ready to be fertilised.

To increase genetic variability a minimum of two males are used to fertilise batches of eggs. To obtain adequate quantities of sperm males are sacrificed and the testes removed. Fertilisation is best effected by first diluting the sperm in physiological saline after which the solution is mixed with the eggs.

Fertilisation can also be caused by squeezing the sperm (milt) directly onto the eggs which have been stripped into a bowl, adding some water (which activates the sperm) and then mixing it thoroughly.

The fertilised eggs become sticky on contact with water and in commercial hatcheries are spread onto mosquito mesh screens, which are suspended slightly off the vertical axis in hatching troughs. If screens are not available the eggs can also be adhered to the roots of floating aquatic plants (such as water hyacinth). During the incubation period development time is temperature dependent.

Once hatching occurs the free embryos fall to the bottom of the tank while the egg envelope remains adhered to the screen. Once a few embryos have hatched the rest follow suit very rapidly. In fact the hatching rate of African catfish embryos is quicker than in most Clariid species. All commercial catfish hatcheries in Southern Africa work at 28oC at which the larvae hatches after 16-18 hours.

Hatching Nourishment and Feeding

After swim-up they flow into rearing tanks. Larval rearing is limited to a 10-15 day duration during which the fish are kept indoors under optimal conditions and fed on a complete dry feed every two hours.

During the first 3-5 days they receive a supplement of Artemia nauplii three times a day. However, catfish larvae can be reared successfully without Artemia or other zooplankton supplementation.

After a 10 - 15 day intensive hatchery period they are transferred to nursery ponds (fertilized and filled two days prior to transfer), at a density of 2,000 fry/m2, or more. During the following 4 - 6 weeks the
juvenile fish are graded into three size classes at least two times.

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The smallest size class is usually discarded each time. The fry are fed every 4 hours, with a 38% protein diet. A water exchange rate of 0.5 l/min/m2
is maintained throughout the phase. At an average weight of 4-5g they are either sold to producers or put into the farms own production ponds.

Average total survival rate from the time of hatching to the end of the nursery phase is 40%. After yolk sac absorption, the larvae are fed on live zooplankton, usually caught from production ponds and are transferred to nursery ponds as early as two days after yolk sac absorption (approximately 5 days old) at an average weight of 5 mg.
The rearing of the larvae to fingerling size under small-scale/subsistence conditions is usually achieved in organically fertilized ponds, filled two days prior to stocking, at a stocking density of 30 to 100 larvae/m2.
In some instances ponds are equipped with compost enclosures covering 10% to 25% of the surface
area. The larval fish are fed on a supplementary basis with substances such as sun-dried brewery waste, rice and wheat bran or other agricultural by-products, if available. Fingerlings are harvested six weeks later at an average weight of 3 to 5g.

Nutrition of Larvae and Early Juveniles

Due to the high thicknesses at which catfish larvae are reared, it is important that a dependable source of high quality larval feed, which satisfies all the
nutritional requirements, is always and readily available.

Live organism, particularly rotifers, cladocerans and Artemia nauplii have been used in the large scale rearing of African catfish larvae. However, the collection of live food from ponds is cumbersome and only available on a seasonal basis and the cultivation of Artemia is expensive particularly for hatcheries in developing countries in Africa.

Because of this, some workers have successfully formulated an artificial dry-feed for larvae, based primarily on a single cell protein (SCP) Torula yeast and fishmeal. Studies on larval nutrition have however indicated that live-food is essential for the first few days after the start of exogenous feeding.

The minimum requirement is an Artemia nauplii
supplement for the first 4 - 5 days after the start of exogenous feeding, during at least three of the 10 - 12 daily feeding periods.

In semi intensive and intensive hatcheries a number of different successful feeding strategies have been used. In Southern Africa larvae are normally reared in the hatchery and fed to satisfaction at two hourly
intervals. This continues for 10 - 14 days at temperatures of 28oC at stocking densities of ca.100 larvae / litres. This protocol results on an acceptable growth rate and survival (80%) at a low cost.

The larval period has been divided into an early phase, when a specific larval diet (consisting mostly of live food) is required, and a later period when the larvae and early juveniles are less dependent on live food.

Experience has shown that the earliest time that larvae should be weaned onto a dry feed is approximately 4 - 5 days after the start of exogenous feeding. Weaning onto a dry diet takes placey gradually during the 10 - 15 day hatchery period.
The proximal composition of an optimized dry feed for early juveniles consists of 55% protein, 9% lipid
(1:1 plant and fish oil mixture). 21% carbohydrate, with a methionine supplement of 150ug / g food.

Vitamins and minerals are usually added to the diet as per the requirements of channel catfish, on the assumption that they are the same. It has been shown that larvae and early juveniles require at least 1500ug ascorbic acid / g dry weight of food and after approximately 6 weeks the gross dietary protein requirement decreases to between 38 - 42%.

Nutritional Requirements during the Grow-out Phase

From the age of six weeks the dietary requirements of African catfish do not seem to change, except that ration size decreases with increasing body size. As the fish grow larger their relative consumption rates
decrease from approximately 10% of body weight per day (at 4 weeks) to around 2 - 4% of body weight per day (at 10 weeks and older).

Similarly growth rate decreases from 14% (at 4 weeks) to 2% at 10 weeks and older. At this stage the best growth rates and feed conversion ratios are achieved with a diet containing 38 - 42% crude protein and an energy level of 12 kJ/g.

Programmed least-cost formulation is a widespread technique used in the animal feed industry. It is aimed at finding the cheapest way of combining a given set of ingredients with a known nutritional
composition, while at the same time satisfying the requirements of the animal concerned and obtaining maximum growth at least cost.

During the grow-out phase the fish should be fed twice a day. The recommended daily ration must be adjusted according to temperature
and fish size.

Fish Pond Preparation and Management

Management skills are needed to run an effective farm. Effective management means proper and timely maintenance of the farm in order to meet up with demand. This means carrying out all activities on the farm and installations which include,

  • successful broodstock manipulation,
  • seed production,
  • stocking,
  • sorting of fish into sizes,
  • disease and pest/ predator control,
  • proper water management,
  • control of human poaching,
  • timely harvesting,
  • marketing,
  • and adequate record keeping.

Site Selection

All meteorological and hydrological information about the area
(generally available from a reconnaissance survey), such as

  • range,
  • mean monthly rainfall,
  • evaporation,
  • sunshine ,
  • wind speed and direction,
  • flood,
  • water table, e.t.c., have to be assessed.

In inland aquaculture, the most commonly used installations are earthen pond farms (rearing and nurseries ponds) and hatcheries therefore, soil characteristics, the quality and quantity of available water and the ease of filling and drainage by gravitational pull are very essential.

The nature of site vegetation indicates the soil type and elevation of the water table. Dense vegetation, particularly tall trees make clearing more difficult and expensive while high ground-water level may create problem of poor drainage and inconvenient use of mechanical equipment for pond construction.

Pond Construction
The pond is the environment where the fish is reared and where all activities relating to its life takes place (from stocking to cropping).

A pond may be earthen or tank. If the pond is earthen, it could either be drainable or undrainable. A Drainable pond is constructed in such a way that water flows into the pond easily by gravity via inlet pipes from a water source and the same pond could be easily emptied also by gravity through outlet pipes buried in the soil. No mechanical energy is needed to carry out either operation and although it may be slower, it saves cost.

An undrainable pond may have inlet pipes to bring water into the pond, but requires mechanical assistance to empty the pond. This type of earthen ponds are usually more expensive to maintain. However, a survey has shown that the construction and operation of a farm with a pumped water supply system can be more economical than that of a tidal water farm.

A Fish tank may be concrete, fibre glass, plastic or wooden and in various sizes and shapes ranging from circular, rectangular to trapezoidal forms for different sizes of fish. It could be sub-surface or made to be completely surface and it is expected that such is protected with locks to prevent human pilfering.


Soil Test
Soil analysis of the intending fish pond site is an often over-sighted but very important activity to be undertaken when a pond is to be constructed. The quality of soil is important in pond farms, not only because of its influence on productivity and quality of the overlying water, but also because of its suitability for dyke construction. The ability of the pond to retain the required water level is also greatly affected by the characteristics of the soil.

The kind of soil tests required before establishing a fish pond can vary from simple visual and tactile inspection to detailed subsurface exploration and laboratory tests. Sandy, clay to clayey loam soils are considered suitable for pond construction.

Texture (relative proportion of sand, silt and clay particles) and porosity are the two most important physical properties to be examined. By mere touch and feel, one can determine the texture of a soil sample. A sample of soil that is malleable and can be shaped into any form without cracks is clayey. If it is not malleable and remains separate with visible grains when dry, then it is sandy. If the sample does not fall into either of the two categories, then it can be categorised as silt or loam.

Water Availability

Availability of good water both in terms of quality and quantity is very essential for successful fish farm operations. The availability in required quantity is particularly important in land based aquaculture systems. It is therefore prescribed to investigate thoroughly, the extent and seasonality of water sources as well as liability to pollution, which may arise from agricultural run-offs, industrial effluents, sewage disposal and flooding.

Toxic substances in water supplies can affect your fishery, particularly in hatcheries. Regularly sampling the pond water will help prevent a crisis on the farm. Water quality parameters include,

  • pH,
  • dissolved oxygen,
  • nitrite:nitrate ratio,
  • temperature and alkalinity.

Ground water from springs, wells, or underground seepage is the best source of water for fish farms. Other sources of water that can be used are, surface waters, runoff water, and chlorine free municipal water. All sources of water must be clean and free of fish diseases and parasites, nuisance fish, predators, silt, pesticides, chlorine, and other chemicals that are harmful to fish life.

Water quality also restricts the type of fish that can be reared and the rate of production. If a farm is susceptible to flooding, a device called spillway can be used. In a case of abundant rainfall at the beginning of a season, reservoirs can be used to store water for the drier seasons.

Pond Preparation

The pond should be completely drained of water and the bottom allowed to dry till it cracks. Desalting of the pond should be done if the pond is very muddy. While drying the pond, undesirable organisms e.g. Frogs, mollusks, fish predators and aquatic weeds such as Water hyacinth, Pistia, Lemna weeds e.t.c are to be removed. Then the pond is fenced around and all inlet and outlet pipes are properly screened while surrounding vegetation is kept low.

Dense aquatic vegetation occurring either along the pond margin or inside the pond must also be controlled. These weeds compete with the phytoplankton for available nutrient in the pond water and hence diminish overall pond productivity. Unwanted organisms like lizards and other reptiles must be chased out or killed as well as crabs and birds while aquatic macrophytes can be removed manually by hand or cutting, mechanically or biologically using grass eaters or herbivorous fish species e.g. Distochodus spp., Grass carp e.t.c.

Repair of Pond Structures
The essence of site survey and farm planning and design is to ensure convenient and effective utilization of pond or farm facilities once they are properly constructed and fitted. However, it may not be out of place to always ensure that adjoining pond structures such as embankments and monks are checked and repaired if necessary and all cracks and holes sealed before pond is filled up with water.

Similarly, fish screens and water filtering structures if clogged are thoroughly cleaned or replaced, damaged pipes replaced and eroded dykes should be strengthened before stocking of pond with fish. This activities on the farm is synonymous with ensuring the safety of the entire business by minimising risk sources.

Liming and Fertilisation

Liming is done in order to improve conditions for fish production although not in the form of fertilisation but terms of favorable edaphic condition of the pond to bring about increased pond productivity. It also increases soil pH thereby creating room for more available carbondioxide for phytoplankton to photosynthesize.

When pH increases, water is prevented from being acidic and so pond mud is able to enhance solubility of phosphates. Adequate liming aids flocculation of colloidal particles and soil microbial activities thereby increasing the rate of decomposition of organic matter and cycling of nutrients.

Materials commonly used for liming synthesize include calcium oxide(quick lime), calcium hydroxide (hydrated lime), agricultural limestone, basic slag and liquid lime. In the absence of these, wood ashes can also serve the purpose but will require a large quantity in order to achieve the desired performance.

The rate of application of lime in fish pond varies with pH and the amount of clay and organic matter present in it. Agricultural limestone and basic slag are the only liming materials that can be applied in large quantity to a pond before stocking and even after stocking the pond with fish for some make-ups.

Calcium oxide and calcium hydroxide can be toxic to fish and should be applied in small quantity to ponds only before stocking due to their toxic effects. Liming rate range from 200-1000kg/ha of liming material depending on individual potency. The higher application rate is for material like agricultural limestone while the lower application rates go for material like calcium hydroxide. The pond is immediately filled with water to a depth of about 0.6m and left for 2-4 days to observe any leakages or seepages. It is later filled up to the required depth and fertilized.

Fertilisation is done to make water more productive by aiding the growth of natural fish food organisms (planktons). Inorganic fertilizer e.g. Urea and N.P.K. and organic manures are the basic two types of fertilization materials that could serve the purpose.

Stocking
Stocking of pond means releasing into the pond an adequate number of selected fish species to be cultured over a specified period of time,
which are of uniform size. Stocking is usually done a week after fertilization. Usually stocking density (number of fish species per unit area) of a pond is dependent on the system of culturing, which may be
monoculture or polyculture.

Fish fingerlings for stocking ponds can be produced by the farmer himself or purchased from a reputable hatchery and are transported either early in the morning or in the evening.

During stocking of pond, fish should be lowered carefully into the water and allowed to swim out of the container after acclimation in order not to further stress them. The pond should be visited the following morning to check for mortality(ies) and if found, should be removed at once and replaced with healthy ones from the same source. Culturable fish species in Nigeria include Clarias gariepinus, Oreochromis niloticus, Heterobranchus bidorsalis, Lates niloticus, Gymnachus niloticus, Chrischthys nigrodigitatus, Heterotis niloticus e.t.c. and many species of shellfish like Oyster and prawn. These species might do well in other tropical countries.

Fish Diseases

The environment plays a key role in the health status of fish under any culturing system. It is such that a high-density culture pond of Clarias when badly managed becoming conducive for disease pathogen to thrive causing colossal fish mortality.

Fish diseases occur in nature (natural water bodies) and in culture systems (ponds, cages and pens). Occurrence of fish diseases is higher in culture systems than in nature because of the following
reasons:

  • Large quantities of organic materials introduced into the system during supplementary feeding and fertiliser application.
  • High concentration of fish ponds in series with direct water way connections between them.
  • Stagnant nature of fish pond water especially when not under flow through system.
  • Crowded population of fish especially under maximum stocking density.
  • Disease outbreak may also occur as a result of bad or inefficient management practices.

The three most common diseases of cultured catfish are Trichodina infection of the gills, bacteria infection of the kidney and Gyrodactylus infection. Infections by Aeromonas spp., Flavobacterium spp., Flexibacter columnaris, Pseudomonas spp., and Edwardsiella tarda have been identified with catfish species.

Most of these diseases have been traced to the fry and fingerling stages of catfish when brought to the farm for stocking. It is therefore very important to
purchase good quality fish seeds from reputable fish farms.

Accumulation of H2S in pond water is another cause of catfish mortality. Treatment of pond with formalin is recommended before stocking pond with fingerlings.

Fresh good quality water should be pumped into the system to replace poor quality ones in order to improve the condition of the pond and ensure adequate dissolved oxygen level of the pond always.

How Does a Farmer Know His Fish Is Diseased?

Fish is suspected to be diseased when there is a change in the normal behaviour and the physical nature of the fish. An attentive farmer would notice the following:


(i) Swimming sluggishly in an uncoordinated zigzag manner
(ii) Gasping at the surface of the water for air
(iii) rubbing its body against surfaces in the pond
(iv) Loss of appetite,
(v) Looking for shade to avoid light within pond
(vi) Floating with underside (ventral) up
(vii) Failing to respond to fright stimulus
(viii) Crowd at water inflow

Physical Signs of Disease in Fish

(i) Ragged or torn fins
(ii) Lesions or sore in the body
(iii) Loss of scales and body discolouration
(iv) Gills turns pale colour
(v) Loss of weight
(vi) Wearing away of the skin and the gill
(vii) Accumulation of liquid in body cavity.
(viii) Gapping mouth

Types of Diseases

The following are identified types of diseases based on their causes.
(i) Infectious Diseases: These are caused by germs or pathogens such as bacteria, fungi or viruses. They attack living tissues, live and multiply there and eventually cause death.
(ii) Parasitic Diseases: These are caused by organisms called parasites which live in or on other animals, known as hosts. Fish parasites include protozoan, crustaceans and worms. They derive
nourishment from tissue or fluid of their hosts.
(iii) Nutritional Disease: Improper diet such as deficiency or imbalance in the nutrient composition of feeds.

Environmental Diseases: These are caused by pollutants from various sources including agricultural run-offs, industrial effluents domestic effluents e.t.c.

Prevention of Diseases

A fish farmer should aim at preventing rather than
treating diseases. Good farm management is of primaryimportance in avoiding disease and parasite attacks.
Provision of Good Quality and Pathogen Free Water: Ensure that pond and hatchery water is in sufficient quantity and readily available at all times. Water should not be passed from one pond to another.

Control of Wild Fish and Predators: Wild fish live in canals and other natural water bodies. They are therefore potential hosts and vectors for disease pathogens. It is therefore recommended that they
should be bared from gaining access into ones farm by:
- Placing wire mesh screens on all water inlets
- Use of chemical on them before stocking the pond

Stocking Density: Avoid overcrowding of fish at any time particularly during hot weather. Observe recommended stocking rate for each fish species and for species combination.

Broodstock Management: Preventive treatment should be given to broodstock before they are used for spawning. They should be separated from young fish hatchlings as soon as possible.

Pond Conditioning: Pathogens and diseases vectors develop in cycles. In most cases their spores, eggs and cysts survive in pond bottoms. Periodic drying and liming of ponds kill the eggs or spores
and their intermediate host (e.g. snail and aquatic weeds).

Treatment of Fish before Stocking: Fish should be given bath treatment before stocking. Transfer of fish from small to bigger ponds reduces the chance of reproduction in parasites.

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