Behavioural changes in farmed sea bass (Dicentrarchus labrax) experimentally infected by Anisakis nematodes

Experimental studies on new host-parasite systems involving farmed fish can contribute to our understanding of the host behavioural changes associated with parasite infections, as predicted by the host manipulation hypothesis. This has applied relevance because in offshore farms, intermediate hosts of Anisakis nematodes may come into contact with farmed species, with an actual risk of infection. It could therefore be useful to identify behavioural indicators of infection status to monitor animal health and develop adequate countermeasures. Spontaneous activity, sociability, feeding, predatory response and boldness were evaluated in the three weeks following the infection in farmed sea bass ( Dicentrarchus labrax ) experimentally infected by Anisakis pegreffii larvae. Infected animals displayed a significant increase in food intake that did not affect body weight gain. They also showed increased interest towards a prey model and towards food in a risky feeding situation. While supporting the hypothesis of increased energy drain from infection that promotes increased investment in foraging rather than active host manipulation, the observed changes could constitute preliminary behavioural indicators of parasite infection in farmed fish.