Nile Perch fishing in Lake Victoria is done using gillnets and long lines. These gears have been deployed in the lake indiscriminately to the extent that in early 2000s the species showed signs of over-fishing. To address this situation, a slot size of 50–85 cm total length (TL) was instituted by the partner states to protect immature fish, and large adults to replenish the stocks while at the same time harvesting mature individuals. Catch Assessment Surveys, have been conducted regularly by the partner states between July 2005 and December 2008 to generate data for setting policies, development planning, and management intervention. A study involving two-stage stratified sampling on the Tanzanian side of the lake showed that Nile Perch caught in the minimum legal 5” gillnets were immature by more than 80%. In contrast Nile Perch of ≥85 cm total length, targeted by long-lines, were seldom encountered to validate the upper limit of the slot size. We advise to abolish the upper slot size limit and introduce a lower legal limit of 7” for gillnets.

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Two mesh sizes (5 and 10 mm) usually used to harvest Rastrineobola argentea in Lake Victoria were assessed from April to September 2001 to determine their suitability. It was observed that 13.2% of fish caught in 5 mm and 11.2% caught in 10 mm for April, May, June and July were of a size below maturity (44 mm standard length, [SL]). Mean size of fish caught with the 5 mm mesh was 46.8 ± 1.2 mm and that of fish caught with the 10 mm mesh was 46.8 ± 0.5 mm (SL). Catches per unit effort (CPUE) from the two meshes were not significantly different, with Haplochromis laparogramma (50.1%) dominating the catch followed by R. argentea (48.9%). Juveniles of Nile Perch, Brycinus jacksonii, Brycinus sadleri, and Barbus spp. (0.9%) were caught in small numbers. About half of the females matured at 43.5 mm and the males at 46.6 mm SL. Fish caught with the 5 mm mesh had on average 1050 ± 400 eggs and those caught with the 10 mm mesh had 918 ± 281 eggs, but the difference was not significant. However, a significant difference was noted between non-infected fish (1050 ± 400 eggs) and fish infected by the cestode Ligula intestinalis (663 ± 316 eggs). Given the absence of differences in key parameters under investigation between the fish caught with the 5 and 10 mm mesh sizes, the two meshes can be used interchangeably.

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