Pond culture is the most popular method of growing tilapia in the world. They are grown in fertilized ponds where the fish utilize natural foods from ponds.
The major problem to overcome in this system is the prolific breeding of the fish that occur in ponds under mixed sex culture. This breeding if not controlled results to overcrowding in the ponds and small size fish (less than 100gms) which may not be of market value. Therefore strategies for producing tilapia in ponds should aim at controlling spawning and recruitment.
a) Mixed-sex culture
In mixed-sex culture of tilapia, both males and female are cultured together but harvested before or soon after they reach sexual maturity. The disadvantage in this is that fish is harvested at a smaller size due to the limited growth period.
In this culture practice, fish are usually stocked at low rates to reduce competition for food and promote rapid growth. One month-old, 1-gram fry are stocked at 1 to 3 per square meter into and grown for about 4 to 5 months. In cold areas where the water temperatures are low and therefore slow growth, tilapia might not reach marketable sizes in that period.
Newly-hatched fry should be used all the time because older ones will reach sexual maturity at a smaller, unmarketable size. They could also be mature fish but stunted. Supplemental feeds with 25 to 32 percent protein are generally used. The average harvest weight is about 250 grams, and total production about 0.25 Kgs/sq m for a stocking rate of 1 fish/m2. Higher stocking densities can be employed to achieve higher production but must be combined with better management. Expected survival is about 80 percent.
In Kenya two to three crops of fish can be produced annually depending on the water temperatures.
b) Mono sex culture
To overcome the problem resulting from prolific breeding of tilapia, ponds are stocked with males only because the males grow almost twice as fast as females.
Male fingerlings can be obtained by three methods:
- Sex-reversal and
- Manual sexing.
None of these methods is always 100 percent effective, and a combination of methods is recommended. Hybridization can used to produce better results of males only. The hybrids can then be subjected to hand sexing and/or sex-reversal treatment. Sex-reversal requires obtaining recently hatched fry and rearing them in tanks or hapas where they are subjected to hormone laced feed for about three weeks.
Tilapia males are preferred for culture because they grow faster than females. All-male culture permits the use of longer culture periods, higher stocking rates and fingerlings of any age. High stocking densities reduce individual growth rates, but yields per unit area are greater. If the growing season can be extended, it should be possible to produce fish of up to 500 grams. Expected survival for all-male culture is 90 percent or greater.
A stocking rate of 2 fish/m2 is commonly used in Kenya to achieve yields of 1kg/ m2. At this stocking rate the daily weight gain will range from 1.5 to 2.0 grams. Culture periods of 6 months or more are needed to produce fish that weigh close to 500 grams. There are cases in Kenya where stocking densities of 6 juveniles/ m2 is practiced with a production of up to 3kg/ m2.
Higher stocking densities will require water aeration and sub-optimal feeding rates may have to be used to maintain suitable water quality.
Tilapia are frequently cultured with other species, mainly catfish (Clarias gariepinus) to take advantage of many natural foods available in ponds and to produce a secondary crop, or to control tilapia breeding. Polyculture uses a combination of species that have different feeding niches to increase overall production without a corresponding increase in the quantity of supplemental feed. Polyculture can improve water quality by creating a better balance among the microbial communities of the pond, resulting in enhanced production.