Image Credits: WorldFish

by Regina Pasipanodya

Tilapia is an inexpensive, commonly consumed fish that is farmed all over the world. It is a lean source of protein that is also high in several vitamins and minerals, such as selenium, vitamin.

The name is driven from its market name of a variety of mild-flavoured, inexpensive freshwater fish species commercially farmed, harvested, and consumed throughout the world.

Tilapia is a popular fish for aquaculture as it is very versatile and is tolerant of a variety of aquaculture environments; it can be farmed in brackish or salt-water and in pond or cage systems.

It can withstand a wide range of environmental conditions, including high salinity, high temperatures, high ammonia concentrations, and low oxygen levels. This makes tilapia very suitable for aqua-farming.

As an omnivorous animal, tilapia eat both animal and vegetable origin as well as algae/plankton. It has been noted by  several farmers that Tilapia can cope with a relatively low feed quality, making them a suitable species for feed of a lower nutritional value than might be necessary for some other aquaculture species.

Breeding

Most farmers prefer to keep only male tilapia in the grow out stage. Male tilapia has proved to be more profitable as they grow bigger as compared to female tilapia which tend to waste energy and time due to breeding.

Due to the rivalry nature of male and female tilapia, most farmers try to keep only male tilapia in grow out. Various techniques are currently in use to try and produce only male tilapia offspring.

Tried and Tested tilapia reproductive methods

Methyltestosterone technique (MT)

This method involves adding methyltestosterone to the juvenile diet. This effectively makes females develop as males whilst the males are left unchanged. No residue from the chemical is left in the fish at harvest as it disappears after 30 days, but this technique still faces ethical and safety issues. It has been reported that this method can cause a degree of liver damage to the fish.

YY Method

This technique produces YY chromosome males.

The first-generation fry is treated with estrogen so that all XY females are produced. These are then mated with males that are known to be XY. This generation are then mated with XX females.
From this, it can then be determined which breeder fish are YY ‘supermales’ as they will only produce XY male offspring.

Hatchery Systems

For best hatchery practice it is sensible to stock one male to three females. In order to prevent the females from incubating their eggs orally, the eggs should be removed. This allows for better control of hatching and allows for the female to produce the next batch of eggs. For creating the best health conditions and for having the most control, tray hatching can be a more effective method to use. However, the drawback of this is that it is very labour intensive and therefore not the most cost-effective technique.

Post-hatchery

Once hatched, fry is then collected and moved to grow out ponds.
Unlike other fish, tilapia tend to be hardier against poor water quality. Best practice states that the dissolved oxygen level should be around 4mg/l. Low oxygen levels in water often lead to mass fish deaths but tilapia can cope in dissolved oxygen levels under 2mg/l, however it is not advised to let the quality reach this low as it will affect the growth performance, quality and health of the fish.
In terms of pH, tilapia can tolerate a wide range but a pH over 6.5 is good for algae growth which is useful as feed for the fish. Temperatures around 25ºc are most favoured by the fish.
Tilapia can be stocked at densities up to 60 kg/m cubed (depending on water and management conditions). However, high stocking densities may have a negative impact on growth performance and health status. Low stocking densities, however, can often lead to aggression between the fish.

Fish Killing

Despite its drawbacks, ice slurry is still the most common killing method used. This raises several welfare concerns regarding delayed loss of consciousness, adverse reactions and pain. Although the fish may become motionless, it may still be conscious for many minutes. Using ice can also lead to the fish meat quality being reduced. A preferred method, when used correctly, is electric stunning. These systems are effective at killing instantly and maintaining fish meat quality.