Age and growth rate estimations as a basis for assessing the population dynamics of Hydrocynus vittatus Castelnau 1861 in the Sanyati Basin of Lake Kariba, Zimbabwe

Abstract

In early fish life stages, information on their age structure can be used to clarify the effects of environmental changes on their growth and survival, thereby providing an improved understanding of factors affecting their recruitment success. There is currently inadequate understanding of the age structure of Hydrocynus vittatus in the Sanyati Basin of Lake Kariba in Zimbabwe. Accordingly, the present study investigated the age of tigerfish in the Sanyati Basin of Lake Kariba using whole otoliths and scales for comparison. The results indicated ages read on the basis of scales and otoliths of H. vittatus agreed to a larger extent for fish aged one to four years than for fish older than four years. There was a significant difference (χ² = 8.520, p = .024) in the ages obtained from analysis of scales and otoliths for fish older than four years. The average percentage error and coefficient of variation were found to be 6.03% and 8.1% for whole otoliths, respectively, for the present study. The APE and CV values for scales were 13.81% and 17.41%, respectively. Relatie age data for whole otoliths fit the von Bertalanffy growth model, while that for scales did not fit the von Bertalanffy model, resulting in many outliers and much scatter of the data. The whole otolith parameters for the von Bertalanffy growth curve were L-infinity = 682.5 mm, k = 0.530 and t₀ = 3.19. Based on the results of the present study, it can be concluded in this case that whole otoliths were the best method of ageing tigerfish from Lake Kariba. Accordingly, it is recommended that otoliths be used for ageing tigerfish in Lake Kariba and that scales be used for ageing tigerfish only up to four years in age.