Prospects of selecting for late maturity in tilapia ( Oreochromis niloticus) : I. Family studies under laboratory conditions

Abstract

The experiment described was undertaken to investigate the selection prospects for changing sexual maturity to a later stage in Oreochromis niloticus under controlled laboratory conditions. Estimation of genetic parameters was based on the performance of 91 full-sib families with an average of 72 offspring. Sires were mated to at least two females which allows variance components to be estimated on a half-sib family basis as well as on a full-sib family basis. On the basis of a standard testing procedure developed earlier, full-sib families were raised separately until the age of 136 days and then slaughtered for examination of the stage of maturity by measuring the gonad weight, the gonadosomatic index in both sexes and visual classification of gonadal development in females. The estimated heritabilities indicate that all traits of gonadal development and also of body development are clearly genetically controlled. Trait variability, especially in gonadal development, turned out to be extremely high, which, in combination with medium values for heritability, suggests very promising chances for selective changes both in gonadal development and growth. Since genetic correlation between gonadal development and growth is zero in females and slightly negative in males, selection for late maturity can efficiently be combined with selection for fast growth.