Technical notes on structures of small-scale freshwater fish farming in Tunisia

In this study, we present the technical characteristics and the methods applied for fashioning different types of cages used in the aquaculture of Nile tilapia. This study was based on experiments made in geothermal water and fresh water reservoirs in Tunisia. The structures showed high efficiency in small-scale freshwater fish farming. The results of the growth of tilapia fry, reared in the two areas, showed a wide variation. However, with regards to cages’ effect on its behavior and growth rate, a negligible influence was noted. In fact, after the pre-growth phase of the fry in cages in geothermal waters during 35 days, we obtained a daily growth rate (DGR) of 0.41g/day and a specific growth rate of 7.11%/day. These changes are superior to those found in freshwater cages whose DGR was around 0.18g/day and specific growth rate (5.98%/day). Besides, the grow-out trials carried out in the SidiSaad, Ghezala and Lahma Reservoirs have given encouraging results with respective densities of 75 P/m3, 77 P/m3 and 61 P/m3. The use of 2m3 and 3m3 cages, which are relatively of low cost, showed high efficiency during their handling, such as good shape retention in water and especially low mesh clogging. According to the results of the present study, it is recommend the use of cages with a volume of 50m3 above the water surface in order to prevent fish jumping out of the cage, also the assembly of the cages for pre-growth and the grow-out must be carried out within the same reservoir in order to minimize the production costs.