Age and growth of Clarias gariepinus (Pisces: Clariidae) in the P.K. le Roux Dam, South Africa

Abstract

Pectoral spines from 350 Clarias gariepinus from the P.K. le Roux Dam were sectioned near the distal end of the basal groove. There was a linear relationship between spine diameter and fish length. Of the spine sections 86% had clear growth checks, which were laid down annually in winter. Age and growth were back-calculated from spine sections. No sexual dichotomy was found in growth. C. gariepinus in the P.K. le Roux Dam have two growth stanzas, the first in fish <500 - 600 mm and the second in fish >500 - 600 mm. It is postulated that these stanzas may be caused by a switch in diet from invertebrates to fish, although the second stanza is probably accentuated by the methods used, which selected for faster growing, larger individuals. The length and mass frequency distribution, condition, size at sexual maturity and growth of C. gariepinus in the P.K. le Roux Dam are compared to those of C. gariepinus populations from other localities.