Nairobi, March 17 -- In the past, I used to catch at least one Nile Perch weighing at least 80 kilogrammes every month, but nowadays it takes years to find one of that size," said Roger Kibalama, a fisherman at Lotoboka landing site in the Ssese Islands, an archipelago of 84 islands located in Lake Victoria.

The Nile Perch, which was introduced to Lake Victoria in the 1950s and has for years been a sure-fire winner for the lake's fisherfolk, is a large predatory fish that feeds on other fish species and can grow up to two metres long and weigh up to 200kg.

Lake Victoria is the world's largest tropical freshwater lake, spanning Kenya, Uganda, and Tanzania and supports the livelihoods of at least 40 million people. The lake is also one of...