Interactive effect of Water temperature, nitrate fertilizers and sewage effluent on development, growth and survival of embryos and early life stages of African Catfish Clarias Gariepinus ((BURCHELL 1822)

This study assessed the interactive effect of water temperature, nitrate fertilizers, and sewage effluent on development, growth and survival of embryos and early life stages of African catfish Clarias gariepinus. One hundred fertilized eggs were incubated and 30 hatched larvae of C. gariepinus were reared in 1000 mL glass flasks for ten days. Three experiments were conducted. Experiments I and II took a 3 x 5, while Experiment III took 3 x 4 x 4 factorial laid out in a completely randomized design. Embryos and larvae were randomly exposed to three temperature levels (25, 28, and 31ºC) in all experiments and five nitrate fertilizer levels (0, 5, 10, 15 and 20 mg/L of NO3-N) for Experiment I, five sewage effluent levels 0%, 15%, 30%, 45%, and 60% for Experiment II and four nitrate fertilizer levels (0, 5, 10, 15 mg/L of NO3-N) and four sewage effluent levels (0, 20%, 40% and 60%) for Experiment III in triplicates. Data were subjected to two-way ANOVA for experiments, I and II and three-way ANOVA for experiment III. Orthogonal polynomial contrasts were used to partition significant nitrate and sewage effluent rates into linear, quadratic, cubic and quartic components. The results showed that, the maximum tolerable range of C. gariepinus embryos and larvae to nitrate fertilizers reduced from 15 to 20 mg/L of NO3-N at 25°C to 10 to 15 mg/L of NO3-N at 28°C and 31°C, while that to sewage effluent reduced from 30% to 45% at 28°C to 15% to 30% at 25°C and 31°C for the embryos and between the control and 15% at 25°C to 31°C for the larvae. The three-way showed significant interactions in the hatching period for the embryos and both yolk absorption period and rate for the larval stage. This study concluded that the effect of both nitrate fertilizers and sewage effluent and their combination on development, growth and survival C. gariepinus embryos and larvae depended on temperature. It is therefore recommended that catfish should be bred and raised in water containing less than 10 mg/L of NO3-N and 15% sewage effluent at 25°C to 31°C