Potential effects of environmental enrichment on seabass behaviour: from group to individual level

Abstract

[eng] A function-based approach of appropriate welfare in aquaculture consists in the ability of the fish to adapt to its captive environment and keep its biological functions correctly working. Environmental enrichment (EE) has been considered as a highly recommended tool to guarantee or improve the welfare of laboratory or captive fish over the last years. As the fish are reared in large numbers at high densities, most farmers usually use behavioral welfare indicators to assess the condition of the whole group. However, behavioral responses are dependent also on the coping style that characterizes an individual. The European seabass(Dicentrarchus labrax) is one of the most important fish species in terms of aquaculture production in Europe. Given that it is a very sensitive species to stressful conditions, the aim of this work was to analyze the effects of EE on seabass behavior, as a proxy of its welfare status. The spatial distribution and the growth performance were tested at group level, while the exploratory behaviour and learning process were assessed individually by risk-taking test. Fish were maintained during 29 days with structural EE showed no differences in growth performance and spatial distribution. Despite of that, the behavioural responses were different in seabass during feeding period. Regarding individual behavioral measurements Stress Coping Style (SCS) the fish reared under control condition showed higher exploratory activity. However, one of the control tanks presented an abnormal behaviour compare to the rest possibly due to its spatial location within the hatchery. Moreover, without including this tank, the treatment had no effect on the risk-taking test until the last week. Furthermore, the enriched fish showed a tendency of learning trough the weeks. These differences are indicative that enrichment could promote behavioural plasticity and proactive behaviour which might be advantageous for the aquaculture. This study evidences positive effects of structural enrichment on seabass behavior, but also that the aquaculture industry needs to further research this topic considering species-specific biology and behavioral characteristics before implementing environmental enrichment protocols.