W. Abbink

The impact of elevated water nitrite concentration on physiology, growth and feed intake of african catfish clarias gariepinus (burchell 1822)

The nitrate threshold concentration in rearing water of African catfish (Clarias gariepinus) was assessed. Female African catfish with an initial mean (SD) weight of 154.3 (7.5) g were exposed to 0.4 (Control), 1.5, 4.2, 9.7 and 27.0 mM nitrate for 42 days. Mean (SD) plasma concentrations of nitrate increased from 71 (29) to 6623 (921) lM at the highest ambient nitrate level. Mean (SD) plasma nitrite concentration ranged from 1.2 (0.5) to 7.9 (9.0) lM. Haematocrit, plasma concentrations of non-esterified fatty acids (NEFA), cortisol, glucose, lactate, osmolality, gill morphology and branchial Na/K-ATPase activity were not affected. Feed intake and specific growth rate were significantly reduced at the highest nitrate concentration. We advise not to exceed a water nitrate concentration of 10 mM (140 mg L 1 NO3-N) to prevent the risk of reduced growth and feed intake in African catfish aquaculture.

Stunning and killing of farmed fish: How to put it into pratice?

In this article an approach is presented to implement stunning and killing of farmed fish in practice. First, in a laboratory setting, the conditions need to be established to achieve an effective stun without causing avoidable distress and discomfort. Product quality is evaluated to assess the impact of stunning method on carcass quality. During subsequent implementation in a commercial setting, it is likely that stress-physiological and neurophysiological measurements are not feasible and, therefore, only behavioral and physical measurements can be performed. Finally, stunning and killing of farmed fish in practice should be controlled using a process-oriented quality assurance system.