An experimental fishing with bottom-set gillnets
of different mesh sizes was carried out in Parakrama
Samudra, a man-made reservoir in Sri Lanka, from
May to September 1983. The optimum retention length
of Oreochromis mossambicus, the dominant fish species
in the reservoir fishery, was estimated for each
mesh size using the Holt method. The optimal length
of 0. mossambicus is a function of mesh size and is
described by the equation; Y = 3.4763 + 0.2024X
\ tUn) £r = o#9920; p ^0.01) where Y = optimal length
(total) in cm and X = stretched mesh size in mm.
Using this relationship and other information on
the desirable landing size of 0. mossambicus for
optimal utilization, the minimum permissible mesh
size for the gillnet fishery is estimated to be
102 mm. The importance of revising the existing
mesh size regulations to optimize the fish production
in the gillnet fishery of the reservoir is discussed.