Early life history of Engraulicypris sardella (Cyprinidae) in Lake Malawi

Abstract

Engraulicypris sardella is the basis of an important artisanal and subsistence fishery in Lake Malawi. It is a small pelagic cyprinid growing to a maximum length of 13 cm and is the only fish species in the lake known to have pelagic larvae. Seasonal abundance and vertical distribution patterns of larvae were investigated in the offshore pelagic zone from March 1992 to January 1994.There was no evidence that E. sardella is a pelagic spawner. Growth rates were estimated by counting rings on the asteriscus otolith, and biomass and production calculated using a length dry weight regression relation ship. Distinct seasonal patterns were observed in the total numbers, biomass, production, and mortality, of larvae that were similar in both years of sampling. Mortality of larvae was lowest from July to December and highest from January to April. Mortality was, on average, higher in the south of the lake, and lower in the central and northern region. Low mortality of larvae coincided with the windy mixed period when primary and secondary production were at a maximum, and correlated with an increased food supply at this time. It is suggested that the strength of the recruiting population is determined by mortality in the larval phase, rather than by the spawning stock biomass. Larvae were found to be most abundant in the upper 50 m of the water column during the clay and were virtually absent below 250 m. Larvae moved down by an average of 50 m at night.