Prospects of selecting for late maturity in tilapia ( Oreochromis niloticus) : II. Strain comparisons under laboratory and field conditions

Abstract

This investigation deals with the question about the extent to which results on the genetic control of maturity with one population of Oreochromis niloticus (Lake Manzala) under laboratory conditions can be generalized. In particular the following two main problems were studied: 1. (1) The validity of the genetic parameters measured under laboratory conditions for commercial production conditions in the tropics. 2. (2) The range of strain variability in gonandal development and growth performance. A representative outbred sample of the reference strain O. niloticus Lake Manzala tested under laboratory conditions was subjected to a full-sib family test under commercial farming conditions at the Baobab Farm, Mombasa, Kenya. The testing procedure was organized in an analogous way to that under laboratory conditions, with slight adaptations to local conditions. Despite significantly slower growth under tropical conditions, there was no indication of greater differences in the genetic parameters. Genetic variability turned out to be as high under tropical as under laboratory conditions. Other populations (strains) tested under either laboratory or field conditions also showed very similar genetic structure in the two main traits of concern. Under both laboratory and field conditions, significant differences between strains were evident, particularly in gonadal development. Some of the strains included matured so late that the variability of the onset of maturity could not be sufficiently analysed by the standard testing procedure applied. According to findings up to now, there is no indication that breeding results obtained under laboratory conditions cannot be directly transferred to commercial production conditions in the tropics. Furthermore, the results of the strain comparison clearly show the need for a very careful selection of the basic population when starting up breeding programmes for late-maturing tilapia with high growth potential.