The Natural Spawning Cycle of the Common Carp (Cyprinus carpio L.) in the Victoria Reservoir
SHIRANI NATHANAEL and UDENI EDIRISINGHE
The common carp (Cyprinus carpio L.) has established a breeding population contributing between 35-40% by weight to the commercial fishery of the Victoria reservoir despite the absence of stocking since 1990. A sample of fifty fish was examined monthly from May 1996 to April 1997 and the mean size at maturity, size frequency distribution and individual fecundities of gravid females were estimated. Seasonal changes in sex ratio, the frequency distribution of female gonadal stages and the gonado-somatic index were also analyzed and used for the determination of the spawning cycle.
The overall female to male ratio was 1.14-1.00. The females were single spawners and individuals with a total length of 30.8 to 46.0 cm and a weight of 530.62 g to 1.990 kg had a fecundity between 49,070 and 240,100. Ovaries were classified into seven maturity stages. Ovaries in spawning condition were present throughout the year indicative of year round breeding. Seasonal variation in mean monthly gonado-somatic index indicated the presence of four possible breeding seasons coinciding with the end of the monsoon and inter-monsoonal rains.