ASPECTS OF THE BIOLOGY OF TILAPIA RENDALLI IN THE DOORNDRAAI DAM TRANSVAAL

Abstract

Scale studies indicated that the annulus is a reliable year mark. A linear relationship existed between scale radius and body growth enabling back calculations to be made. The growth rate of males in Doorndraai Dam were similar to findings in the Incomati and Limpopo systems by Gaigher 1969 and Potgieter 1974 for the same species. The average sex ratio was one male to 1,8 females and was similar to that of the above river systems. Males reached sexual maturity at 12 cm while females matured at a length of 15 cm. The spawning season extended from late September to after December. Fecundity increased with an increase in length from 3 600 ova for a 15,4 cm fish to 8 500 for a 30,9 cm fish. T. rendalli fed extensively on macro-phytic vegetation when it was available, otherwise they became facultative feeders.