Available information and fresh evidence is presented to show that presently, commercialTy^mportant indigenous cyprinid species such.as Puntius sarana and Labeo dussumieri of the Parakrama Samudra reservoir as well as other species like P. dorsalis etc. which are known to-const-itute a significant fish biomass of the reservdir but commercially yet unexploited, are not likely to breed in the reservoir. Possible reasons for an apparent lack of breeding success in the reservoir are briefly discussed. In addition the possible effects of water level fluctuations in the reservoir on the nest building capability of the exotic cichlid. Sarotherodon mossambicus, which is the mainstay of the commercial fishery are discussed. It is postulated that a certain degree of fluctuation in the water level is essential for S. mossambicus to maintain its breeding success. Possible impact of the likely reproductive migrations.of some of the indigenous'cyprinids, which are shown to be seasonal, and the variation in the breeding success of S. mossambicus in relation to water level fluctuations on the ecosystem, as a whole, is briefly evaluated, qualitatively.