News and knowhow for farmers

Converting female to male tilapia fish is more productive

As many counties move to empower youth and women groups through aquaculture, small-scale fish farmers can increase productivity by introducing only male fingerlings into their ponds.

Increased local and global demand, more-so for tilapia, catfish and corp, is driving more people into this farming.

Monosex fishing farming, which is advocating male fingerlings, has been found to be high yielding because of the biological disadvantages of females.

In counties like Mombasa, catfish has been the main species given out to these farmers.

For instance Nile tilapia, which is one of the most preferred fish globally, is easy to rear because of its omnivorous feeding orientation.

This characteristic of eating both plants and small animals gives it a cutting edge over other species in food resource strained environments.

Males do best

In addition, its prolific reproduction rate makes it a choice for many farmers.

On the flip-side the fast multiplication impacts yield per single fish. Multiple researches have shown that rearing only male tilapia can increase the weight of an individual fish by 30 per cent.

On average, a mature tilapia fish weighs about between 400g to 500g in five to eight months. In warmer and stable conditions tilapia can reach 600g to 900g, according to Food and Agricultural Organisation.

FAO says growth rate of males, when alone, is almost twice per day. The energy meant to spur reproduction in the males supports growth.

Peter Ogora, an animal breeding lecturer at Egerton University, says continued reproduction hinders fish from attaining maximum weight. 

“Fish grow well when the population is kept constant. Reproducing females increase population of the stock, effectively raising competition for food an other growth resources. This results in stunted growth of the original stock,” the aquaculture lectures said.

Given that tilapia is a mouth brooder (rearing fingerlings in the mouth), it is likely to have limited time to feed as it secures the fingerlings against predators, he said.

READ ALSO What could be killing Kirinyaga catfish

Males become females

But farmers cannot convert tilapia fish to males on their own. Fish fingerling breeding firms do the conversion of females into males before selling.

The conversion is possible because sexual differentiation in tilapia fish takes place several days after yolk sac absorption. For successful reversal, fries (‘candidates’) must be less than 14 mm.

A male sex hormone, methyltestosterone, is introduced into feeds. If this, and other procedures are followed, 95 per cent to 100 per cent conversion is achieved.

READ ALSO: Fish farming in rice paddies.

Another alternative of female-to male reversal that firms are using is subjecting the fries into ‘sustainable temperature treatment’.

The later method is becoming more popular as eaters shun inorganic foods. This has made the companies avoid hormonal sex reversal process.

Jambo Fish Western and Jambo Fish firms in Nairobi’s Kasarani are some of the distributors of the male fingerlings.

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