BRACKISHWATER TOLERANCE OF SOME SPECIES AND HYBRIDS OF OREOCHROMIS FOR USE IN LAGOON AQUACULTURE (IVORY-COAST)

For a decade, the Ivory Coast has undertaken the promotion of its large lagoons by developing aquaculture in general and the culture of tilapia in particular. Thus far, only the feasibility of Oreochromis niloticus culture in freshwater has been demonstrated. Since only a very small area of the lagoon network is freshwater, any significant increase in tilapia production depends on their culture in brackishwater under satisfactory technical and economic conditions. Neither O. niloticus nor the lagoon species, Sarotherodon melanotheron and Tilapia guineensis, are suitable for culture under these conditions. An experimental program was set up to select a tilapia with high survival rate and fast growth in brackishwater. This program involved the species O. aureus, O. mossambicus, O. urolepis hornorum, and the hybrids O. niloticus x O. aureus, O. mossambicus x O. niloticus, O. niloticus x O.u. hornorum and O. mossambicus x O.u. hornorum. The trials were held in lagoon water with a salinity of up to 15 ppt, the maximum value recorded for the zones suitable for aquaculture in the lagoon. These trials allowed the selection of one species, O. aureus, and two hybrids, O. niloticus x O. aureus and O. mossambicus x O. niloticus with survival rates significantly higher than those of the other groups tested. Comparison of the performances and respective advantages of these three groups leads to the choice of O. aureus in preference to the hybrids for brackishwater culture. The results of the present study are discussed in relation to salinity tolerance and growth data found in the literature about the species and hybrids tested.