Conclusions
This study clearly demonstrates that plasma levels of NH4
+,
cortisol, glucose and lactate, as well as plasma osmolality are not
indicators of first choice for chronic toxicity of high water ammonia in
African catfish. We advise for African catfish not to exceed a water
NH3 concentration of 24 μM (0.34 mg NH3-N/L) to reduce the risk of
reduced growth and feed intake. Below this NH3 threshold concentration
less obvious, but potentially dangerous disturbances such as
deteriorated gill fine structures are avoided.