Zimmermann, E.; Purchase, C.F.; Fleming, I.A. (2012). Reducing the incidence of net cage biting and the expression of escape-related behaviours in Altantic cod (Gadus morhua) with feeding and cage enrichment. Applied Animal Behaviour Science. 141 71-78.
The escape of fish from aquaculture is a persistent economic problem for farmers as well as an environmental problem that threatens wild fish population as a consequence of potential negative ecological and genetic interactions. Farmed Atlantic cod (Gadus morhua) cause significant damage by biting the net and creating holes through which they escape. We determined the role of food, cage enrichment, net damage, and individual temperament on net biting behavior. During four separate trials, net interactions by fish were observed in relation to combinations of the above treatments. Fish with no access to food and in plain (not enriched) cages interacted the most with the net wall, with 7.5 and 12.6 more interactions per h, respectively, than fish with food that were in enriched cages (food P = 0.01; enrichment P < 0.01). Of the stimulating objects used to enrich cages, 97% of interactions were with the tubes that provided refuge (P < 0.01). Cod were attracted to damaged areas of net, interacting 0.12 more times per h than at undamaged areas (P < 0.01). Individuals showed consistent behavior over time, but there was no relationship between temperament and net interactions (P = 0.17). The results indicate that appropriate feeding levels and cage enrichment may lead to reduced net interactions and thus fewer holes, reducing the potential for fish to escape.