Introduction to fish farming
Fish production is from 3 main sources:
By artisanal fisheries
These are local fishermen and women who fish either on parttime or full time basis employing all sorts of gears and techniques. Some of the methods are destructive e.g. use of poisons-crushed fruits. The common feature of these approaches is that almost all the fishes irrespective of size are captured.
By industrial/commercial trawlers
Industrial fishing in in-shore and offshore water of the seas. The UN law of the sea allows coastal countries the exclusive right to fish in zone up to 200 nautical miles (320km) from her coast. This zone is known as the Exclusive Economic Zone
(EEZ). The establishment of national jurisdiction in this zone offers each country the chance to exploit the benefits of the zone for its country. Intense and uncontrolled exploitation of the fishes in the EEZ has resulted in dwindling catches and remarkable reduction in the catches of some species e.g. the tongue sole. Cynoglossus senegalensis.
By fish farming
Fin and shell fishes can be produced in some systems e.g. ponds, cages, pens, raceways etc as a result of over-exploitation from the wild. Any over-exploited species can be hatchery raised/reared and restock into the natural waters. Therefore, practical handling and care of fish is crucial in fish production to achieve the goal of providing enough quantity of fish for consumption especially through pisciculture.
Practical handling and care of fish
This is the very first step in fish production especially through aquaculture source because there cannot be harvest without recruitment. It entails all the precautionary steps and techniques to protect the fish especially from the seed stage to adult stage when it appears on the table for consumption.
The fish seeds (fry and fingerling) are usually ‘nursed’ rather than reared to ensure proper recruitment or else the harvest will be low. All processes e.g. the contact materials with fish (fish seed), water treatments, fastness during operations etc are referred to as the practical handling and care of fish to ensure the success of each venture into fisheries management.
For example, as a rule, gear that is used for collecting fish especially fish seed is constructed of fine mesh (<10mm) netting materials and should inflict minimal physical injury on the body.
These gears include: drag net, lift net, cast net, clap net and traps.
When using nets or traps to take fingerlings or adult fish out of ponds, care must be taken during seining since muddy water can stress the fish. To reduce mortality due to muddy seining, fish could be attracted with crumbles of feeds, light source or dewatering.
Other practical handling and care of fish can be hinted as
- Always use wet hand/ contact materials e.g. nets
- Handle the fish gently
- Keep fish in water while counting
- Avoid overcrowding the fish in containers
- Avoid standing fish in the sunlight and for a long time
- Fill containers for transport with pond water
- Transport fish during cool weather
- Work fast and travel quickly
- Avoid squeezing, throwing or dropping fish
- Always check temperature and temper fish
Tempering is a pre-stocking treatment of especially fish seed. It involves homogenizing the water in which the seeds are transported with the water in the pond/system into which they are stocked. It is a crucial step in handling and care of fish to avoid high mortality.
Fish breeding is synonymous to fish propagation which simply means multiplication. Breeding entails all the various techniques or methods which can be used or at least maintain a fish stock (i.e. methods of fish seed production).
This concept in fish production is important when an increase demand for fish and for culture is considered. Also, in tropical world, many fish species breed only once a year. Therefore, a continuous demand for fish seed makes fish propagation sine-qua-non. There are various techniques which differ from different parts of the world depending on local conditions and available local facilities.
For instance, in developing world where facilities are not available, fish seeds are obtained from the wild while in advanced countries where there are facilities, propagation is completely artificial.
Basically there are 3 types of fish breeding/propagation
- Natural propagation/breeding techniques
- Naturally induced breeding/pond or enclosure propagation
- Artificial propagation through hypophysation.
Natural breeding technique: is a technique whereby fish are allowed to breed in their natural environment and their eggs, larvae, fry and fingerling are collected for pond stocking.
The collection of fish seed is carried out with no physical damage to the seeds which entails the elimination of gill-nets and hooks as used gears. Gears for collection include the hand net; lift net, drag/seine nets, cash nets. Light is used to attract them at night, pieces of feeds, GNC can also be used to attract them to avoid mudding during seining. Special traps especially in streams and river could be used. Before transportation, the collected fry are fingerling are kept in Happa, net or pots and starve overnight in clean water to avoid defaecation which can utilize O2 during
transit. The collected fry and transported in well aerated, cool water to the pond for stocking.
Problems associated with natural breeding technique include:
- For many species, the seed may not be available as and when needed or required. Hence, there is shortage of fingerling for stocking leading to low fish production.
- Weed fishes and fish enemies e.g. Dragonfly larvae, water bugs which may feed on eggs or attack the fry or compete for the fish food may also be collected with the fish seed. Fish parasites e.g. leeches are collected with fish seed from the wild and introduced inadvertently into the rearing ponds.
- Difficulty of accurate identification of the fry/fingerling stages of certain species which results in the desired species being stocked with undesirable stunted species. e.g. observed in catfish with Barbus.
- There is high mortality during catch/collection and at transportation.
- May be uneconomical e.g. cost of going to the wild, pay workers to gain access to the spawning sites through trial and error methods.
However, natural breeding technique needs little or no skill which is an advantage.
Ponds or enclosure propagation
Essentially it is a naturally induced breeding technique that involves introduction of broodfishes or brooders into specially constructed ponds or tanks and allow them to breed. It is a common practice to leave the brooders breeding repeatedly.
This is not ideal in terms of quality and is anti-selective since the age and parentage of the fish cannot be determined after some time. Therefore, a proper and systematic pond propagation technique that would ensure production of fry of known age is recommended.
Usually, ponds used for propagation are small, about 0.1ha or 100m2 and shallow usually less than 1m. Cement/concrete tanks with measurements of 5x3x1m have been successfully used for pond propagation of Tilapias .
Some fishes which reproduce easily in ponds are
Carps and Gymnarchus breed in special ponds. Intensive efforts are going on to propagate Chrysichthys in ponds.
For example, the propagation of tilapias in ponds does best in shallow waters and the pond must have sandy bottom. If tank is used, the floor of tank is usually covered with a layer of sand for making their nests (spawning area). The eggs hatch within 1-2days after external fertilization. These hatchlings/larvae are usually carried by one of the two parents until they are free to go or fend on their own. The fry move in shoals (school) along the edges of the
water from where they can be collected.
- Discuss the newly designed special receptacle for propagating tilapias.
- Discuss pond breeding of Heterotis, Gymnarchus which require some stimuli to effect breeding in enclosures.
These species would not breed in ponds without submerged higher plants e.g. grasses. In case of Clarias, it requires moving water and hence an artificial water current of the water must be created. Carp requires a special pond called Hoffer or Dubisch pond and it must have a large bottom with grasses and it is shallow.
Temperature and dissolved Oxygen are crucially and optimally required in the ponds. In addition, the water must be free of other fishes especially the carnivorous ones e.g. Hemichromis. Also, mention the success story so far about
Chrysichthys breeding in an enclosure. The above techniques are simple and inexpensive in addition to achieving the best possible survival rate, good growth and health for the fish. The techniques require no sophisticated installations or tools and without difficulties and risks involved in artificial fertilization.
Pond types required for fish farming
- Segregation pond.
- Spawning ponds
- Nursery pond.
- Fingerling pond.
- Rearing pond.
- Stocking ponds.
Precaution of fish ponds :-
- Pond should not be porous
- Optimum PH 7 to 8.
- It should be well drained and aerated.
- Acidic ponds are treated with the right dose of calcium carbonate powder.
- Excessive weeds can be control by mechanism chemical or biological treat.
- Well manuring and throughout watching are necessary.
Summary about ponds
the selection of site and construction of the fish pond must be based on ,expert plan the selection of site should be the nearby source of water which may be strummed or river or artesan well or rain water. Availability of cheap agricultural production to feed fish also needs to be considered “Transportation” facility is a important factor as, it is essential to bring the needed commodities to the pond or to market fish High water table shows no problem in retaining water in pond may or brick ponds both ,can be used for framing special care has to be taken for spreading about 6 inch of surface soil,along the top of the slope and also with bottom of the pond.
Artificial Propagation through Hypophysation
The hypophysation technique which uses the pituitary gland (the hypophysis) to induce spawning in fish can be carried out at any time of the year and under any environmental conditions. The technique ensures fish seed availability at all times of the year.
For instance, using this technique a single common carp (Cyprinus carpio) has been induced to spawn five
times within a year at intervals of 60,62,41 and 186 days between successive spawning, even though carp breeds naturally only once a year.
Artificial propagation was first described in 1765, but was neglected until 1842 when it was described again. A number of experiments were carried out and by 1937 artificial propagation at commercial level was attained. By 1964, it has spread to many parts of Europe, America, Japan, China, Israel but to date there are increased trials in Africa with varying degrees of success.
Privately owned fish farms have tried hypophysation using catfishes e.g. Clarias gariepinus, Heterobranchus bidaorsalis. For the purpose of easy description and discussion, artificial propagation can be divided into 6 stages as:
- Selection of brooders
- Maturation of the brooders
- Stripping i.e. obtaining eggs and sperms (milt) from the brooders
- Incubation of fertilized eggs to ensure that they hatch
- Rearing of the larvae/fry up to fingerling stage.
On the whole, more fry can be obtained from an individual fish through artificial propagation involving stripping after hypophysation when compared to what is obtained through other propagation techniques.
- Fish seed is guaranteed all the year round
- Fish seed is obtained outside the natural environment of fish.
- It increases the survival rate of the fry
- It improves quality by crossing two different species (i.e. hybridization) can be obtained.
- The donor fish has to be sacrificed in most cases and hence of loss of fish.
- The whole process is laborious and highly technical.
- Very expensive in that it requires proper housing, constructions of tanks, installation of jars in a close circulatory system.
It should be noted that artificial (i.e naturally induced or through hypophysation) production of fish seed are carried out in enclosures known as Hatcheries which may be an indoor or outdoor facilities and they require inputs such as brood stock, adequate water supply and suitable feed. The sequence of steps involved in artificial production of seed can be schemed as:
Management/Maintenance of Broodstocks
Maintenance or management of broodstocks on a breeding farm is very necessary because it permits the build-up and selection of healthy, high quality brooders for stock improvement.
In ponds for keeping broodstocks, they need to be simulated to that of the fish’s preferred habitats in terms of O2 content, temp, pH, tranquility, size and depth of the water, stocking density and quality and enough food.
Sharp fluctuations in the physico-chemical parameters of the water in the enclosures or ponds must be prevented especially temperature and O2 as these are known to inhibit gonadal development. Overcrowding in the pond conditions must be avoided because it constitutes negative stress on the stock, though many cultured species are able to tolerate some degrees of crowded pond situations.
For example, brooders of catfish (Clarias) are held at a stocking density of one fish in 2.-5.0m2 of pond area with the depth of 1.0-1.5m.
Frequent disturbances also interfere with normal gonadal development and therefore care must be taken to restrict seeing or netting of the fish to the minimum.
For example Clarias being hardy can withstand being netted out of water two or thrice a week, other fish species should not be seined more than once a week.
Provision of suitable and adequate quantity of food is equally of great importance. It has been known that brooders reared or maintained on adequate natural food and/or protein-rich artificial feed have a higher fecundity of larger eggs and thus yield best results.
To prevent outbreak of diseases in the stock used for breeding or subsequent transmission of any diseases to the offspring, brooders should be routinely treated and bathed in a 25% NaCl or 150ppm formalin solution for 10-30minutes.
Malachite green can also be used.
Maintenance or management of brood stocks kept depends on the species, their size and the no
of eggs per Kg per female, the survival from fertilized egg stage to the fry stocking phase and the demands for the fish from the grow-out units. On principles of brood stock management solve the following problem with the students.
As a fishery consultant, you have to supply one million Clarias gariepinus fry for restocking a Government farm.
- How many eggs of this species will you require to produce the fry assuming that the average female brooder produces 5600eggs per kilogram body weight and that only 90% of eggs spawned are viable and of these, 86% will be successfully fertilized and out of these, only 78% would hatch?
- The average weight of each female Clarias as at the time of this contract was 3kg.
Calculate the number of female brood stock to be maintained that would produce the above eggs to supply the required numbers of fry.
- If the sex ratio of male to female to effect the breeding was 2:3, how many male would be required, assuming each weighed 2.4kg to effect the above fry production?
- For proper management, at least thrice the required brood stocks must be maintained in a brood stock pond at a density of 600kg per hectare. Calculate the surface area of the pond required to maintain the brooders that would ensure the above fry supply.
Management of Fish seeds (Fry and Fingerling)
In fish life history, egg(fertilized) Larva fry fingerling sub-adult/juvenile adult. The larval stage ends when it fills up its air bladder with air, begins swimming in a fish-like manner and starts to eat external food that it becomes to fry.
In addition to needing all the essential requirements of the larva e.g. adequate O2, suitable temperature, removal of
waste matter etc, the fry also requires external food which should be adequate both qualitatively and quantitatively.
The early fry may still have a part of the yolk left and can draw on it for sustenance from 1-4 days depending on the species. The fry spends this period and learns to find its own food.
Fry are said to require a more precise and careful nursing to ensure their survival and proper growth. Authors have remarked that lack of suitable food
caused high fry mortality.
Fingerling is bigger than fry e.g. 5-10cm and it is the stage that is usually stocked.
Management of these developmental stages is based on their fragility and difference in sizes in terms of their habitats, stocking density, feeding and control of their infections and diseases. These stages are crucial because there cannot be harvest without recruitment. Hence, these stages are called fish seed or recruits.
Fry are nursed in small earthen ponds which vary from 100-200m2 for about 3-4 weeks to attain fingerling stage.
Fingerlings are reared rather than nursed in bigger earthen ponds. The pond is usually prepared to have a standing crop of rotifers and must be checked to exclude cyclopoid copepods which are natural enemies of fry.
Food is crucial for growth which mustbe observed daily.
Fry have two sources of food during the initial stage – yolk and external food to ensure better survival. Maintain these.
It is part of the management that mixing of different age groups of same species should be avoided and it is advisable to use a monoculture of fishseed.
The most commonly provided artificial feed is finely ground and sieved through 100-150µm mesh called starter food. After two weeks, the size of feed particles is increased. Cutting the grasses on the dyke and throwing them around the shallow part of pond helps to increase natural food production in the pond.
After about one month, the young fingerling have to be removed from the small nursing pond and stock in a large pond. The artificial feeding continues but the size of food changes due to changes in the size of mouth. It is necessary to thin out the stock in order to provide sufficient space, O2, food to the fast growing fingerling.
Enemies of these stages must be managed too. These enemies change with the age of the fish. These are categorized as
(i) enemies of fry
(ii) enemies of advanced fry and
(iii) of fingerlings.
Identify these enemies and treat adequately. For example enemies of fry include carnivorous Cyclops, insect and insect larvae (e.g. dragonfly), which predate largely on the fry. It has been stated that Cyclops are responsible for the highest mortality of fry at this stage next only to that caused by hunger. The advanced fry is less prone to predation by Cyclops since it is more agile and its skin in thicker and stronger. It is the insect larvae that pose greater danger
at this stage followed by hunger if there is acute food shortage.
O2 deficiency may kill in heavily manured ponds.
Abrupt changes in temperature and extreme cold may exterminate the fry population.
Enemies of the fingerling – Besides hunger, O2 deficiency, sudden change in temperature, white spot disease caused by Ichthyophthirius, Trichodina and gill worm infections could exterminate the entire stock within a brief period in fingerling ponds. Consult your note on Pathology for effective treatments. Preventive and control methods of these infections would be discussed during class interactions.
Infection of a pond with any protozoan or bacteria or fungus can be diagnosed through certain indicative signs such as:
(i) swimming of fry/fingerling in large school near the surface
(ii) their accumulation below the water inlet
(iii) the occurrence of dark specimens
(iv) sudden occurrence of dead fish on the surface. It should pointed out that fish that die because of parasitic infection only float on the surface while those that die due to dietary factors remain at the bottom.
Procurement of feed and system of feeding
Intensive fish culture involves a high/heavy stocking of water impoundments/enclosures and the use of artificial/formula feeds to improve production. Fish feed provide nutrients for optimal growth and this rapid growth achieved implies that fish feeds are essential for the economic use of time. Through shortened grow-out periods, a fish farmer can effect two croppings within a year. The increased number of croppings of table-sized fish imply that
more profit can be generated by the fish farmer.
Therefore, feed of adequate nutritional value is the foundation on which fish farming is built. Good and high quality feeds improve the quality of the edible portion of fish, enhances high protein retention and gives the flesh a firm
consistency and delicate flavor.
Types of foods: Based on the source of origin, there are natural food and artificial feeds.
Natural fish food can be of animal origin which include zooplankton e.g. rotifers, protozoans, cladocerans, copepods, larger zooplankton (arrow worms, crustaceans etc, benthic invertebrates e.g. polychaetes, molluscs, insect larvae e.g. Chironomids and Chaoborids, forage fish and aquatic insects.
Natural food could be of plant origin as an phytoplankton e.g. diatoms, desmids, blue-green algae, unicellular, filamentous and colonial algae and aquatic macrophytes. Dead plants and animals (i.e. decaying organic matter called detritus) also constitute an important natural food
Artificial feeds: Under commercial culture condition involving high stocking densities of fish, natural foods become limiting. It is the artificial or supplementary diets that fill the shortcoming of natural foods.
Early efforts to provide supplementary diets for cultured fish were based on attempts to duplicate composition of natural foods. This was labour-intensive involving the growing of earthworm and insects, harvesting small fish or tadpoles or by processing agricultural slaughter house by-products not readily consumed by man. Such diets had a number of drawbacks e.g. poor growth and nutritional diseases which led to the development of dry or semi-moist feeds commonly used nowadays. Artificial feeds are available in:
- Type I – meals, pastes or cakes
- Type II – pellets
- Type III – semi-moist feed
Type I is for plankton feeders, algae grazers, fry, small fingerling. They may be prepared as dry meal, colloidal suspension or soft cakes. Fish consume them by direct capture or by filtering water.
Type II – This type is convenient for storage, transportation and dispensing in automatic feeder or self feeder. Many fish feeds are prepared in pellet forms which can be hard (sinking), expanded (floating-encapsulated) or soft pelleted. Hard pellets may be used for fish with a mouth size capable of ingesting them, the stomach capacity to store them and the peristaltic action and enzymatic ability to digest them. Uneaten pellets disintegrate slowly in water and hence cause less water pollution. To discuss the merits and demerits in class.
Floating or expanded feeds enable the fish farmer to observe fish feeding at the pond surface. Floating feeds are acceptable to most surface-water feeders as well as catfish. Floating feeds are more expensive than hard pellets because they require extra energy in extrusion process and increased drying time. Soft pellets have water content between 8-20% and are preferred by fish which strike for their food.
Type III – Semi-moist have water content in the range of 37-40% and are prepared from frozen or fresh, wet ingredients. They are the most expensive feeds available hence fish farmers are not interested in using them.
Feeding systems or techniques
A feeding programme is successful when the required amount of nutritionally adequate feed is consumed. The feeding plan and techniques are affected by fish species and size, time of the year and the type of production system.
The best guide for the fish farmer is to place the feed where it can be obtained by the fish, offer it so that the fish will receive their share/rations. Floating feeds can be broadcast mechanically from specially designed feeding troughs or from mechanical feeders. For small ponds, the feed can be distributed by hand (self feeder). Feeding of fry and small fingerling poses different challenges.
The experienced fingerling producer knows where the young fish are located in the pond. He may use containers or shelters to attract or hold the newly-stocked fry in an area. Note that feed placed in wrong location will not be eaten and will reduce overall water quality.
Mechanical feeders include the demand type which is activated by the fish and the automatic type which is activated by a time clock. Both have serious limitations, one of which is the tendency to less frequent observation of the culture system.
The demand feeder is useful in extensive systems where fish do not have to be observed closely e.g. in lakes, reservoirs.
The automatic feeder is designed to offer a measured amount of feed at predetermined time of the day.
Relationships between feeding and production will be discussed in class.
Test-cropping and Grading
Before harvesting, there is the need for test cropping and/or grading for at least once a month after stocking of the fish into the production ponds. A farmer needs to make direct assessment of the status of his fish stocks over the growth period because there are some species especially the carnivorous species e.g. Clarias which exhibit hierarchical dominance in its feeding behavior.
As a result, the more aggressive will be at an advantage to receive more food than others bringing about marked differences in sizes of individual fish. Not only this, test cropping allows to monitor the health status and adjustments in the feeding rates to account for growth especially if artificial feeding is practised.
The test cropping involves capturing a few number of fish using cast net or seine net early in the morning of a cool day and a bowl/bucket of water is kept nearby to keep or hold the fish during examination.
The fish is held in a wet cloth or foam and any surface with which the live fish makes contact during the examination must be thoroughly moistened / wetted. If large variations in size among individual fish are observed, the stock should be graded into appropriate size groups and probably restocked into different ponds if not ready for
Grading can be carried out by eye or where large numbers of fish are to be sorted out for harvesting, a box with a bottom that consists of a series of bars or slots appropriately spaced to segregate the specific size range of fish can be used.
Grading also functions to produce equal-sized fish for the market at the time of harvesting.
However, it should be noted that test cropping and/or grading during production period should not be more than once a month because it is stressful to the fish and they tend to go off their food for a few days.
Precuration of fish
1 health males and females are required for breeding.
2 isolation of pairs before spawning.
3 male and female kept at the ration 2 to 1 in spawing ponds.
4 full protection of freshly laid egg is necessary.
advantage of fish farming
1 supplies the necessary amount of proteins in the form of meat .
2 fish oil and code liver oil having high values.
3 unwanted weeds can be controlled for example in paddy cum fish culture.
4 helps to control harmful aquatic insect and larvae.
5 protection of fishes from extinction.
6 except releases by fish as good sources of manure.
7 maintenance of the balancing ecosystem in the pond and lake.
8 upgrade the economic condition of farmers.
Definition of Aquaculture:
Fish production was previously heavily dependent upon capture fishery and in particular the marine resources. However, the capture fishery cannot be expected to be a perennial protein donor. Moreover, a substantial portion of the marine catch is being utilised for making industrial products which are not directly consumed by man.
Therefore, a viable alternative by which fish production could be increased through a popularized biotechnique, called aquaculture. Aquaculture may be defined as the “farming and husbandry of economically important aquatic animals and plants under controlled conditions”.
The term ‘aquaculture’, though over a decade has been widely used, still has a misconception by many users.
Aquaculture is sufficiently expressive and multifaceted. It includes the following aspects:
(1) The type of organism cultured. For example, the culture of fish, prawn, oyster, mussel, seaweed, etc.
(2) The type of culture technique, such as pond culture, raceway culture, cage culture, pen culture, raft culture, etc.
(3) The aquatic environment in which the culture is done such as freshwater, brackish water or salt water.
(4) A specific factor of the environment used for culture, such as cold water or warm water aquaculture.
Although aquaculture is considered to be a branch of fisheries science, still there is a tendency to denote the distinction between the two because of some of the basic differences in development and management.
Salient Characters of Aquaculture:
(1) High Productivity:
In comparison to agriculture or veterinary practices, aquaculture has been found to be more productive.
(2) Integrated Farming:
Aquaculture with agriculture, horticulture or animal husbandry is found to be more profitable,
Aquaculture gives efficient means of recycling domestic and/or agriculture wastes and thus, helps in protecting our environment.
(4) Rural Development:
Aquaculture helps to integrate rural development by generating employment opportunities and would thus help to arrest the exodus of population from rural to urban areas.
(5) Intensive Fish Culture:
In aquaculture practice, owing to the fishes three-dimensional utilization of the water body can be crowded more closely (200/ m3) and grown through water re-circulation system. This gives high yield of about 25 t/ha/year.
(6) Earning Foreign Exchange:
Commercially important items, such as ornamental fishes, Artemia cysts, prawns, lobsters, crabs, frog legs, etc., produced through aquaculture are highly valued and can earn good foreign exchange.
Fish seeds and larvae of economically important fishes of capture fisheries are artificially recruited in fish hatcheries through aquaculture, called ranching or aquarange farming. It is commonly known as “culture based capture fishery” and involves restocking of the wild stock for harvesting. This process has replenished the dwindling stock of rivers and seas.
(8) Replenishment of Coral Reefs:
Coral reefs that have been destroyed naturally or anthropogenically are being replenished through construction of artificial coral reef.
(9) Creating Leisure-Time Activities:
Leisure- time activities can be maintained through sport fishing and creating home and public aquaria.
(10) Mariculture and Fisheries Enhancement:
In many reef areas the use of mariculture is fast growing. It provides an alternative source of income and employment in coastal areas. Replenishment schemes of species that has been greatly diminished has been undertaken in certain areas. This has been useful for returning species such as giant clams and trochus to reefs where they have been largely or completely exterminated by overfishing.
(11) Promoting Agro-Industrial Development:
Aquaculture can promote agro-industrial development through:
(i) Processing and marketing of fishery products, feeds and equipment for aquaculture,
(ii) Seaweed culture for the production of marine celluloids, and
Types of Aquaculture Practices:
I. Depending on Hydrobiological Features:
Depending on hydrobiological features (particularly salinity) aquaculture is divided into following:
(b) Brackish water,
(c) Metahaline, and
Various types of culture practices are carried out in each of these divisions (Fig. 6.5).
(a) Freshwater Aquaculture:
Freshwater aquaculture includes culture of various economically important aquatic organisms in small impoundments.
They are as follows:
(i) Composite fish culture or polyculture or mixed fish farming:
Fast growing compatible species of fishes with different feeding habits are cultured together.
(ii) Monosex Culture:
In this culture, separate sexes of individual species are cultured. By this method the yield can be enhanced.
(iii) Monospecies Culture:
This is concerned with the culturing of individual species of fish.
(iv) Jeol Fish Culture:
Shallow water bodies with poor oxygen content is used for culturing air breathing fish species such as Channa, Clarias, Heteropneustes, etc.
(v) Predator-Prey Culture:
Predator-prey (murrel-tilapia) culture is also undertaken in shallow waters and in swampy areas. Here, predator fish like murrels are cultured along with their prey-fish, tilapia.
(vi) Culture of Fishes in Temple Tanks:
The quality of the water in the unutilised temple tanks are poor owing to stagnation. Such tanks can be utilised for the culture of fishes such as common carp, murrel, tilapia, catfishes, etc.
(vii) Culture of Fishes in Irrigation Tank:
Irrigation tanks are fitted with inlet and outlet water sources, which can be profitably utilised for culture of Indian major carps and exotic carps.
(viii) Raceway Culture:
Raceways are series of rectangular or circular earthen or cemented tanks which is constructed in such a way that a running water system like that of a stream is maintained (Fig. 6.6).
In such culture sewage water after treatment in oxidation ponds are utilised. Such water contains high nutrients which are responsible for production of plankton bloom, the food of fishes.
(x) Fish Culture in Recirculating System:
In areas of water scarcity, the recirculatory system of fish culture is practised. Hence, water is circulated continuously through a biological filter.
(xi) Ornamental Fish Culture:
Ornamental or aquarium fishes (Fig. 6.7) such as guppy (Lebistes reticulatus), gourami (Trichogaster trichopterus), goldfish (Carassius auratus), molly (Mollienisia latipinna), siamese fighter (Betta splendeus), sword tail (Xiphophorus helleri), etc. are cultured due to their high demand in international market.
(xii) Culture of Larvivorous Fishes:
Larvivorous fishes such as Oryzias melastigma, Aplocheilus blochii and Gambusia sp. are cultured. These fishes help to control the vectors (mosquito, etc.) and can save the human population from many diseases.
(xiii) Integrated Fish Farming:
Here along with the culture of fishes, agricultural crops (rice, banana, etc.) or livestocks (pig, poultry, duck, cattle, etc.) are cultured so as to get more return.
(xiv) Culture of Sport Fishes:
Cold water fishes such as trout, salmon, etc. are cultured due to their sport value in places of high altitude like Himachal Pradesh, Kashmir, Kodaikanal, etc.
(xv) Culture of Plankton and Other Fish Food Organisms:
Mass culture of protein-rich live fish food organisms such as plankton (cladocerans, rotifers, copepods, etc.) and tubifex worms, is being done as they are essential for growing larvae of fin fish and shellfish in culture systems.
(b) Brackish Water Aquaculture:
Brackish water areas are rich in oxygen and plankton. Brackish water organisms such as milkfish (Chanos chanos), Lates calcarifer, Mugil sp. prawns, mussels, etc. can be cultured in various ways such as in tidal ponds, pens, cages or by rack, raft or rope culture (mainly in case of oysters). Mangrove crab, Scylla serrata, are also cultured in the shallow brackish water regions by constructing bamboo cages.
India has a long coastal and open sea area, which offers wide scope for culture operations of fin fishes and shellfishes. For the culture of fish, prawns and lobsters floating cages are used. Racks, rafts, rope, pole and long lines are used for culture of mussels, particularly pearl oysters.
Sea-weeds also are widely cultured with the help of nets or webbings.
(d) Metahaline Culture:
In off seasons of salt manufacture, the salt pans are utilised for fish culture. Culture of brine shrimp (Artemia salina) can be undertaken in these supersaline salt pan (salinity more than 200%) area. The nauplii of Artemia serve as a protein-rich live food for the fin fishes and shellfishes. The dormant eggs (cysts) of Artemia formed under unfavourable conditions also can earn good foreign exchange.
II. Depending on Motive of Farming:
Depending upon the motive of farming, based on economic and commercial considerations, fish culture practices may be classified as under:
(i) Extensive Fish Culture:
Large ponds, beels, etc. are brought under this culture (Table 6.2) where little care is taken with regard to its improvement. So it is the least managed fish farming. Here, the yield is modest and the expenditure is less as it is raised on natural food.
(ii) Intensive Fish Culture:
In this fish culture (Table 6.2) an all-out attempt is made to achieve maximum production of fish from a minimum quantity of water. It is the best managed form of fish farming and the fishes are fed on artificial food in addition to the natural feed. Here the yield is very high (over 6000 kg/ha/year). Although the cost of investment is high, the earnings from this culture far exceed the cost, so as to ensure high profit.
(iii) Semi-Intensive Fish Culture:
Intensive culture possesses certain hazards, for which a culture between the first two, called semi-intensive culture (Table 6.2), is generally practised. Here certain amount of management is required and the net profit is in between the above two.
III. Depending on Special Operational Techniques:
Based on special operational techniques, fish culture practices may be classified as below:
(i) Cage Culture:
In this culture the fishes are held in a section of water, either in a flowing river or in a big impoundment. The fishes are imprisoned in a cage made of galvanised steel wire frames with nylon meshes or simply of bamboo frames with split bamboo mats. The cages are of various sizes and the commonly used size is about 10 sq. metres.
Cages are of the following types:
(a) Floating cages (Fig. 6.8),
(b) Fixed cages,
(c) Submerged cages and
(d) Moveable cages.
The principal aim of culturing fishes in cages is to practice monoculture of selected species. Cage culture was first started in Cambodia. Since 1980 cage culture has been in practice in India.
Cage culture has proved a boon for reclaiming extensive waste waters, i.e., swamps and derelict waters of Assam, Bihar and Karnataka. Air breathing fishes (Clarias, Heteropneustes, Anabas, Channa, etc.) have responded well to cage-culture practices.
The advantages are:
1. Minimum use of all available water resources.
2. Economic use of water.
3. Easy observation and handling of the fish population on daily basis.
4. It reduces fish mortality.
5. Easiness in the control of competitors, predators and parasites.
6. Easy and complete harvesting of fishes possible.
7. Control of diseases and isolation of the diseased fishes is easy in floating cages.
8. Initial investment is relatively less.
However, there are certain limitations:
1. Risk of theft is high.
2. Adequate renewal of water in the cages for eliminating metabolites is not possible.
3. There is a need for maintenance of high dissolved oxygen content.
4. Fouling agents like snails, etc. accumulate at the bottom of the cage (mesh) which needs periodic removal.
5. The release of uneaten food and faeces adversely affect the water quality.
(ii) Pen Culture:
Pens generally refer to small enclosures used for confinement or safe keeping of domestic animals. In fisheries pens are formed by damming a bay, cove, fjord (an arm of a sea), estuary, river, lake or reservoir. Sites are selected where the barriers can be constructed across narrow sections or channels (Fig. 6.9) in order to reduce costs and increase the ease of operation.
The enclosures should be relatively small (about 2.0-7.0 ha). However, in Japan large enclosures measuring up to 120 ha or more are also seen. The depth of the pens should be more than 1 metre, even in low tide condition.
Most of the perimeter of the enclosure (pen) is formed by the natural shoreline. When the blind end of a water area is enclosed, there may be only one or one series of barriers. In the enclosures where there are continuous flows of water, there may be two or two series of barriers: one upstream and another downstream.
The barriers are made of stones, sand, soil or concrete and are provided with ‘SCREENS’. These ‘screens’ prevent the escape of the fish stock (Fig. 6.10).
The types of enclosures generally seen are:
(a) Bamboo scaffolding enclosures used in the bays of Philippines and in the lakes of China (Fig. 6.10).
(b) Floating net-enclosures useful for the culture of tilapia and milkfish in lakes.
(c) Single-layered pens of nylon webbing.
(d) Double-layered pens suitable for use as nurseries for fish and prawn seeds.
The introductions of pen culture in many countries have not met with much success. This probably is due to the difficulties in the use of intensive techniques and in some cases due to the high costs of embankments and water management (for example, through pumping).
The merits of pen culture are:
(1) As it is a continuous process due to continuous supply of water, production (yield) is greater in a limited space with rich food and oxygen supply.
(2) Higher growth rate is possible as energy is saved towards locomotion, feeding, etc.
(3) It generally generates employment opportunities for the coastal people.
(4) There is less danger of fish mortality as toxic metabolites (ammonia, etc.) are flushed regularly.
The demerits of this culture are:
(1) Unfavourable weather conditions may damage the pen or flood the culture sites.
(2) Pen culture sites may be polluted particularly during the occasional abundance of red tide causing organisms, such as ‘Dinoflagellates’.
(3) Organisms like Balanus and certain algae (Enteromorpha, etc.) may adhere to the bamboo poles causing biofouling.
(4) Terrestrial insects sometimes take refuge in the exposed portions of pens and cause damage.
(5) The nylon-webbing enclosures may be cut and damaged by certain species of crabs.
(6) Predatory fishes sometimes may enter into the pen and cause considerable damage to seed and growing fishes or prawns.
(7) Abundance of sea weeds in the outskirts of the pen, may bring down the oxygen level through release of hydrogen sulphide on death and decay.
Qualities of Culturable Aquatic Species:
In India about 465 cultivatable aquatic organisms, belonging to 107 families of animals and 28 families of plants were catalogued by Jhingran and Gopala- krishnan (1974).
All these aquatic organisms can probably be used for culture and this would be an advantage to choose from such a large number of aqua-cultured species that are adapted to different environmental conditions. This would definitely eliminate the thought of introduction of exotic species for aquaculture.
However, the main question is whether it would be worth to culture all these 465 aquatic organisms and how can all of them contribute to the main objectives of aquaculture.
Another fact is that, in such a case aquaculture would certainly miss the advantages that agriculture have had in concentrating research on a few species that had led to the development of advanced technologies of production of selected high- yielding strains and hybrids.
However, development of such technologies had required a lot of effort and time. Aquaculture science, on the other hand, is relatively new and would probably require much longer time to reach that level of advancement if efforts have to be shared among so many species.
Aquaculture till today, through long traditional experience and scientific research, have actually succeeded in domesticating only a few number of species. This, therefore, indicates that there is a tendency towards limiting the number of species in large scale commercial aquaculture.
At the same time there is a real need to have species suited for different environmental conditions and economic circumstances. Species for aquaculture, therefore, has to be selected according to the objectives of culture.