The status of Oreochromis moseambicus ms investigated in the fisheries of five man-made reservoirs in Sri banka . A declining trend in the mean landing size of 0_. mossambicus ever the last three decades, at least in the cqse of one reservoir, indicates overexploitation. The data suggested that the mean body condition of 0. mossambicus y measured as the theoretical weight of a 20-rn individual (Wgo) i8 negatively correlated (p<0.05) to the percentage of undersized ( 20 cm) 0_. mossambicus in the commercial catches . The low stock abundance of 0. mossambicus in some reservoirs of which the body condition is poor is possibly due to catching individuals before they attain a reasonable size. This situation, called "growth overfishing" is a potential danger in most of the reservoirs in Sri ' Lanka. The importance of maintaining a minimum catch size (20 cm) of 0. mossambicus is discussed.
The low cost and high potential for protein production of freshwater fisheries in rural comnunities, have compelled Sri Lanka to focus on the development of inland fisheries. The inland fisheries of Sri Lanka are almost entirely confined to man-made reservoirs that were constructed for irrigation and hydroelectric purposes.
Since its introduction to Sri Lanka in 1952, Qreochromis mossambicus (Peters), an exotic cichlid, has played a major role in inland fish production. De Silva (1985a) has shown that 0. mossambicus accounts for between 56 and 99% of the total fish yield in individual reservoirs and that, in most reservoirs, the percentage contribution of this species to production is more than 70%. Although invaluable contributions have been made to the development of reservoir fisheries in Sri Lanka (Fernando 1971, 1977; De Silva and Fernando 1980; De Silva 1983, 1985a), the information on reservoir fisheries management is inadequate. A declining trend in the mean landing size of 0. mossambicus has been recorded in Parakrama Samudra, a Sri Lankan man-made reservoir (De Silva 1985a). However, in Sri Lankan reservoirs, no attempt has been made to investigate the effect on fish production of catching small, young fish ("growth . r overfishing") (Gulland 1983).; This paper highlights and discusses the potential danger of growth overfishing in the reservoir fisheries of Sri Lanka.