ASILA ATONGA, A.

KMFRI, P. O. Box 1881, Kisumu, Kenya

Effect of mesh regulation on Nile Tilapia, Oreochromis niloticus (L.) fishery in Lake Victoria.

Gill net trials were conducted in the Nyanza gulf of Lake Victoria between October 1998 and January 1999. Four sets of gill nets were arranged into hanging coefficients of 0.2, 0.4, 0.6 and 0.8. Each set had mesh sizes ranging from 25 mm in arithmetic progression to 203 mm with a difference of 12.5 mm between them. The mesh sizes were arranged randomly in every hanging coefficient.

The objectives of the study were to determine the appropriate hanging coefficient for the Nile tilapia fishery, to derive the appropriate mesh size for the Nile tilapia fishery and to determine the selection factor of Nile tilapia fishery.

Fish specimens were caught in mesh size 25 mm to 199 mm with the number decreasing with increase in mesh size. Hanging coefficient of 0.6 was found to be the optimum for Nile tilapia at a mesh size of 152 mm. Adjustment of mesh size below the optimum observed mesh size led to a decrease in the relative revenue obtained in the fishery.
There is need to increase the mesh size from the current 127 mm to 152 mm in order to conserve the Nile tilapia fishery and ensure rational exploitation of the fishery.