Size at maturity, maturity stages and sex ratio of tigerfish Hydrocynus vittatus Castelnau, 1861 in Lake Kariba, Zimbabwe: assessing the influence of decades of fisheries exploitation

Abstract

Size at maturity, sex ratio and maturity stages are key population parameters in fisheries management of exploited stocks because they influence survival of fish populations. The decline in Hydrocynus vittatus catches during the tigerfish competition and along the  shoreline of Lake Kariba, Zimbabwe prompted this study. This study investigated population parameters of H. vittatus in the Sanyati Basin, Lake Kariba. A gonadal reproductive stage determination index was used to determine sexual maturity and the logistic growth curve was used to estimate size at 50% sexual maturity (L₅₀). The study revealed that the L50 value had decreased from 30 cm to 22.1 cm for males and 35 cm to 27.8 cm for females since 1961. Males and females had an L₅₀ of 22.1 cm and 27.8 cm, respectively. The male to female ratio was 1:0.8, which is typical of stressed populations. Increased fishing pressure in the Sanyati Basin, Lake Kariba is a potential threat to the H. vittatus population. More research and monitoring of the population parameters of tigerfish is required, in order to predict long term effects of overexploitation and to enable responsible authorities to protect the fish stock from collapsing.

Keywords: fish, gonadal reproductive stage determination index, management, sexual maturity