First results of floating cage culture of the African catfish Heterobranchus longifilis Valenciennes, 1840:: Effect of stocking density on survival and growth rates

The main constraint of the culture of the African catfish Heterobranchus longfilis remains the high mortality rate due mainly to cannibalism. Heterobranchus longifilis is generally cultured in earth ponds, tanks and enclosures. Floating cage aquaculture can be an alternative system to these traditional techniques as it may allow predation control. Therefore, the purpose of this study was to test the effects of floating cages (I m 3) on survival and growth parameters of H. longfilis at different stocking densities in man-made Lake Ayame. In a first experiment which started with fish of 0.8 +/- 0.1 g initial mean weight, five stocking densities (50, 100, 200, 500 and 1000 fish/m(3)) were tested during a 90-day experiment. The results showed that unlike final mean weight (WO and mean daily weight gain (Mdwg), weight variation coefficient (final Cv), cannibalism (Cr), mortality (Mr) and survival (Sr) were density dependent: best results of survival, cannibalism and mortality (68.0 +/- 1.5%, 18.0 +/- 2.2% and 14.0 +/- 1.5% respectively) were recorded at the lowest density (50 fish/m(3)). In a second experiment that began with fish of 13.4 +/- 0.5 g (Wi) and lasted for 270 days, the stocking densities tested were 6, 12, 25, 50 and 100 fish/m(3). Results of this experiment showed that all the parameters [Mr, Cr, Sr, final Cv and apparent feed conversion ratio (Afcr)] were influenced by the stocking densities. Higher Wf, Mdwg and Sr and lower final Cv, Cr, Mr, and Afcr were recorded at the lowest stocking densities (6 and 12 fish/m(3)). Cage culture of H. longifilis results in a higher Sr, but a lower Mdwg compared to those usually recorded in traditional rearing systems. However, this low production potential of H. longifilis could be increased by the improvement of rearing conditions (feeding systems, culture management) as noted in other species. (c) 2006 Elsevier B.V. All rights reserved.