The influence of food availability, breeding seasons and growth rate on commercial catches of Limnothrissa miodon (Boulenger) in Lake Kariba

Commercial catches of Limnothrissa miodon in Lake Kariba show clear seasonal fluctuations. Recruitment to the pelagic fishing areas was investigated. A von Bertalanffy growth curve for the species was calculated and the breeding season determined from the calculated hatching dates of observed alevins and juveniles. Distribution of the different size classes was determined by a horizontal transect. Analysis of body composition showed a decrease in total lipids at the time when catches were dropping. This was shown to be due to a decline in triglyceride fat reserves apparently resulting from food stress and possibly resulting in increased natural mortality. Recruitment to the fishing areas and the total mortality rate are believed to cause the seasonal fluctuations in catch. The annual cycle of production may be caused by the summer inflow of nutrients from the rivers. Growth is apparently stunted in comparison to the species' growth rate in Lake Tanganyika, probably due to the lower nutrient status of Lake Kariba.