The impact of elevated water ammonia concentration on physiology, growth and feed intake of African catfish ( Clarias gariepinus)

Abstract

The threshold concentration for NH 3 in rearing water of African catfish ( Clarias gariepinus) was assessed. African catfish with an initial mean (SD) weight of 141.0 (24) g were exposed to five different T amm [sum of NH 3 and NH 4 +] concentrations: 0.37 (Control), 1.06, 2.12, 5.16 and 19.7 mM, which concurs with NH 3 concentrations of 4 (Control), 14, 38, 176 and 1084 μM. Plasma concentrations of NH 4 +, cortisol, glucose and lactate, plasma osmolality, gill morphology, branchial Na +/K +-ATPase activity, feed intake and specific growth rate were monitored. No effect of water NH 3 on plasma NH 4 + concentrations was detected. Feed intake and specific growth rate were severely affected at exposure to water NH 3 concentrations above 90 μM (calculated EC 10 values: 89 and 122 μM). No major disturbances in physiological blood parameters were observed at these NH 3 concentrations, but gill morphology (a remarkably sensitive stress indicator) deteriorated significantly. Based on the lower limit of the 95% confidence interval for EC 10, we advise for African catfish not to exceed a water NH 3 concentration of 24 μM (0.34 mg NH 3-N/L). This finding is relevant for design and management of African catfish production systems.