New functions for the analysis of two-phrase growth of juvenile and adult fishes, with application to Nile perch

Abstract

Two phases of growth can sometimes be distinguished in long-lived fish species. The first involves the growth of zooplankton-feeding juveniles and young adults. The second consists of accelerated growth of large, piscivorous adults. We present modified versions of the von Bertalanffy growth equation that account for this feature and fit them to length-at-age data on Nile perch Lates niloticus (Centropomidae) from Lake Chad (north and south) in north-central Africa, and from Lake Nasser in Egypt. The growth parameters estimated for the new equations allow one to make preliminary estimates of the energy gains by Nile perch associated with transition from zooplanktivory to piscivory.