Evidence of environmental effects on reproductive characteristics of Nile tilapia (Oreochromis niloticus) populations from man-made lakes of Ivory Coast

¹ Orstom, Gamet, Groupe aquaculture continentale méditerranéenne et tropicale, B.P. 5095, 34033 Montpellier cedex 1, France
² Present address: Orstom, Instalasi Penelitian Perikanan Air Tawar, Jl. Ragunan, Pasar Minggu, P.O. Box 7220/Jkspm, Jakarta 12540, Indonesia

Received: 31 October 1997
Accepted: 20 April 1998

Abstract

Large differences in reproductive traits were observed between populations of Oreochromis niloticus sampled in 9 manmade lakes of Ivory Coast. In order to assess whether these variations in reproductive characteristics resulted from short term adaptation or from a longer evolutionary process, living specimens were caught in the two most differentiated populations in term of life history traits, and placed in a common environment in culture conditions. Genetic analysis of fish from these two populations were performed using four microsatellite markers and revealed that both descended originally from the same strain (Bouaké station) which was constituted from broodfish initially caught in the Nile and Volta basins. Fish from the two populations were subjected to a common environment (pond and aquariums) for five months. Then, their reproductive characteristics were analysed and no significant differences were found in fecundity, egg size and spawning frequency. These results indicate that reproductive differences between the two populations, originally observed in the two reservoirs, mostly reflect the phenotypic plasticity of the species in facing different environmental conditions.