Chemical alarm cues in juvenile African catfish, Clarias gariepinus Burchell: A potential stressor in aquaculture?

Previous studies on the effects of stocking density on the behaviour of African catfish have shown that at low densities, especially directly after restocking of tanks, increased aggression might occur. This aggression may directly affect the welfare of the fish. In addition, the resulting skin damage may also lead to the release of chemical alarm cues from the skin of the fish, possibly acting as a secondary stressor in a farming situation. Moreover, in a recirculation aquaculture system, a build-up of chemical alarm cues might occur. The objective of this study was to examine the effects of a single chemical alarm cue administration on the behaviour and growth performance of group-housed African catfish. Furthermore, the effects of a single passage over a biofilter on the behavioural response of African catfish to chemical alarm cues were tested. Although African catfish responded to chemical alarm cues with a short-term 35% increase in the number of active fish, no long-term effects were observed on both behaviour and growth performance of the fish. Furthermore, the results indicated that a single passage over a biofilter did not strongly alter the response of African catfish to the alarm cue, indicated by a 25% increase in the number of active fish. In conclusion, the results of this study indicate that chemical alarm cues, at the concentration applied in this study, cannot be considered a stressor for African catfish, although the effects of higher cue concentrations need further study. In addition, further study into the effects of chemical alarm cues on other, non-predatory, farmed fish is recommended.