Growth, reproduction and population structure of Diplotaxodon limnothrissa in the southeast arm of Lake Malawi

摘要

Diplotaxodon limnothrissa is a widely distributed species occurring throughout Lake Malawi from the surface to a depth of at least 220m. It is probably the most abundant cichlid in the lake, with biomass estimates of around 87 OOOt in the pelagic zonealone. The species is exploited commercially in the southern part of the lake but, since its inception, this fishery has never been assessed. Analysis of sectioned sagittal otoliths revealed that D. limnothrissa is a slow-growing and relatively long-lived species, attaining ages in excess of 10 years. Length-at-age was described using the von Bertalanffy growth model, with combined-sex growth described as L_t= 211.21(1 - exp(-0.24(t + 1.36)))mm TL. Females matured at 139mm TL at an estimated age of 3.18 years. Total, natural and fishing mortalities were estimated at 0.63yr~(-1), 0.38yr~(-1) and 0.25yr~(-1) respectively.