Abundance and Aspects of the Reproductive Biology of Common Carp Cyprinus carpio in an Upland Reservoir in Sri Lanka

Abstract

During the period 1984 to 1990, Victoria, a newly impounded hydroelectric reservoir in Sri Lanka, was stocked with different exotic fish species to augment fish production as a secondary use of the reservoir. A marked increase in relative abundance and CPUE (catch per unit effort) of common carp by the end of 1998, indicates successful natural recruitment to the fishery. The reproductive pattern based on fluctuations of the mean monthly gonadosomatic index (GSI) showed that gonad maturation and spawning were significantly correlated (r s =0.5638; p<0.05)) to rainfall. During peak breeding, the water temperature, pH, total alkalinity, hardness, conductivity, and dissolved oxygen concentrations ranged from 24.4 to 26.0 0 C, 6.9 to 8.1, 39 to 79 mg·l-1 , 44 to 72 mg·l-1 , 53 to 70 µs·cm-1 and 4.4 to 6.5 mg·l-1 respectively. Co-occurring fish species and conditions necessary for fry survival in the spawning habitat were identified. High percentage fertilization and hatchability of eggs indicate that a suitable system could be developed during peak breeding using "kakabans" (egg collectors) made of commonly available coconut fiber as an effective egg deposition substrate, to improve natural spawning conditions in the reservoir.