Effect of light intensity on early ontogeny of African sharptooth catfish, Clarias gariepinus (Burchell)

Light intensity during the early life stages of fish can have profound effects on their survival, developmental rate, yolk utilization efficiency and body size. Here, these aspects were analysed during two separate experiments (with or without exogenous food) on two distinct progenies of African sharptooth catfish, at five different light intensities (<0.1, 70, 500, 2500 and 8000 Lx; 24L:0D, 27.2 degrees C). The duration of the egg incubation period (from 1.01 to 1.25days post fertilization, dPF) was inversely proportional to light intensity, as hatching took place at more precocious developmental stages with increasing light intensity, i.e. at significantly (P<0.05) shorter body length and slightly more abundant remaining yolk at 8000Lx in comparison to <0.1Lx. At the start of exogenous feeding (4 dPF), most of these differences had vanished. During the period of mixed feeding (until the end of yolk absorption, 11 dPF), growth decreased significantly with increasing light intensity. Daily mortality rates after hatching varied very little between light intensities. Mortality during egg incubation increased significantly (P<0.05) with increasing light intensity, whereas it varied very little between light intensities thereafter, with the best survival rates since fertilization until the end of yolk absorption obtained at intermediate light intensities (70-2500Lx). These results could be useful for improving the performance of African sharptooth catfish hatcheries.