What is sustainable Aquaculture?

Sustainable aquaculture is that aquaculture which can be achieved without substantial inputs of energy, feeds and utilizing low density stocking rates of fish and without major environmental manipulations. Primary feeds are naturally produced. Major inputs are labor usually from the farmers family. Operations are characterized by intensive husbandry , low overal capital expenditures and continued production over a long period of time . Due to lower stocking levels the health of the fish is generally much hardier then higher stocking levels due to less stress and less exposure to disease pathogens. Operating equipment is usually low powered aerators or recirculating pumps, if any.

This system is often used for rural pond production without any operating equipment, ponds are stocked with either single sex populations or mass harvested after a rearing time of six to eight months of grow out time and the entire crop sold.

In the most basic mode ponds are stocked and fish naturally produced are harvested by angling or netting. This is the lowest production mode, and when Tilapia are produced without a predator to remove most of the natural fry produced the ponds will soon become over populated and the bulk of the fish will be stunted . Stocking ponds with all males is the simplest production method to produce a marketable crop. The fish can be harvested over a period of time with the \'holding period\' simply allowing the fish to continue growing.

To this model, various techniques can be added to increase production: feeding of natural feeds, such as duckweed and greenwater. Adding fertilizers such as manures to produce phytoplanktons. Growing plants that will reduce nitrates in the water which reduce growth rates, such as water hyacinths, water lettuce or growing edible plants and herbs on floating rafts that reduce nitrates and are harvested for human use.

This model is environmentally friendly with little or no impact on the environment .

GLOSSARY OF TERMS

brackish water- a mix of fresh and salt water.

fertilizer- a substance added to water to increase the production of natural fish food organisms.

fry- recently hatched fish which weigh less then 1 gram or measure less than 2.5 cm in total length.

grow-out pond/facility- a pond or other facility used to grow aquatic animals to marketable size

integrated aquaculture- aquaculture systems with combined livestock and/or crop production. Example, using animal manures to fertilze a pond to enhance fish production and using water from the pond to irrigate a garden.

male hormone- a substance that, when fed to tilapia fry induces undifferentiated tissue to develop into male gnads(testes).

manual sexing - physically examining a fish to determine sex.

manufactured food- commercially processed food for fish or livestock.

mixed-sex culture- culture of males and females in the same grow-out facility.

monosex culture- culture of all-male fish for market.

mouth-brooder- a fish that hatches its eggs in its mouth.

partial harvesting- periodic harvesting of a portion of the fish from a culture facility during a culture cycle.

phytoplankton- the plant component of plankton

plankton-the various mostly microscopic aquatic organisms (plants and animals) that serve as food for larger aquatic animals and fish.

polyculture- simultaneous culture of two or more aquatic species with different food habits.

predacious fish- a fish species that eats other fish for food.

spawning- the act of depositing eggs and producing young.

susstrate spawner- a fish that lays its eggs on some form of substrate or surface where they will hatch.

zooplankton- the animal component of plankton

FRY PRODUCTION SYSTEMS

Fry can be produced in a variety of systems, from catching fry and juveniles by nets or seines from shallow ponds, using pairs or trios of breeders in cages, raising the breeders in tanks/aquaria or raising the breeders in small pools and netting the fry.

By far the system with the most control of production, with least labor input is maintianing the breeders in small pools of 18\" to 24\" depth, and netting the fry and rearing them separately.

The model system that works well for subsistence aquaculture is to maintain breeder groups of up to 3 females per male in 3-4 sq meter pools of about 24\" depth. These can be easily constructed of cement. Large packing crates lined with heavy mill plastic have also been used. Childrens wading pools of comparable measurements are also used. Larger pools with more breeding groups can be used but production control is less. Such a production \'unit\' can produce 1500 or more fry every 5-6 weeks.

Typically all fry are harvested from the pool daily or weekly for 3 weeks to a month, and moved to a growout pool for growth up to ~ 100-150 grams before being moved to a growout pond or pool. The shorter the harvesting period the more unifrom the fry will be in size. This gives better concentration of feeds, and easier to manage the fry. At this stage the fry can be fed \'green water\' of cultured phytoplankton and supplemented with finely powdered flake fish foods.

Because of more crowded conditions in the fry pool some minimal aeration will be a major help to among other things increase disssolved oxygen through moving the surface water and keeping the food in suspension.

SEXING FOR MANUAL SEPARATION OF SEXES.

If the fry are alowed to grow out as produced then early breeding will begin as sexual maturity is reached, which in most tilapia species occurs very young, 3-4 months of age.This will rapidly result in over population and stunting of fish. To prevent this ponds can be stock with all-male fish, this is called monosex culture. Females are rarely used for this as their growth rate is slower then males. Typically the culled females are dried and ground up for fish food, or dried and salted and used for human food.

The fry can be manually sorted and sexed, or chemically treated with hormones for a month to cause the majority of the females to convert to being males. This is an added cost, and will only produce 80-90% males. Manually sorting can produce sexing accuracy of up to 90% males.

Farmers can easily distinguish males and female Tilapia once they reach about 10 cm in length, and about 20 grams in weight by examining the genital papillae on the fishs underside.

In a few training sessions workers can sex up to about 2000 fish a day with accuracy of up to 90%. Some reproduction will occur in the growout pool/pond but most of these fry will be eaten by the larger fish being grown out.

Hold the fish in the hand, or two hands if large, with the belly up; with the thumb you can push the papillae to \'stand up\', to the rear of the anus,

the papilla is a small fleshy appendage which projects from the underside of the fish through which the female passes eggs and urine and a male passes sperm and urine.

looking at the papillae the females will show two holes on it, while the male has just one. The anus is just in front of the papillae The male has one opening for sperm and urine passage wheras the female has two, one for urine passage and one for eggs.


The males can be released into fry pools for further growout/stocking and the females to a tray for drying.

Culture the males for another 60-80 days until they reach 60-100 grams and can be moved to a larger growout pool.

Manual sexing should be done early in the morning to avoid stressing the fish more then has to be. If the males are going into holding containers they shouldnot be overcrowded and the container emptied regularly. If, the sex cannot be determined donot stock the fish. Feeding the fry pool should be stopped about 48 hours before sexing to reduce stress.

Stocking males into growout pools/ponds can be done at the rate of 2 fish per square meter. If the pool is aerated and partial water changes done then this can be increased. Growing water hyacinth on the surface can aid in reducing urea/nitrates in the water and also allow a larger population to be grown. The optimal stocking rate will be achieved through filtration to reduce nitrites/nitrates, aeration and periodic water changes. Sustained production of a kilo of fish per cubic meter of water can be achieved