The effects of stocking density on fish welfare

Abstract

The welfare of intensively farmed fish is a subject of increasing interest and one of the principal areas of concern is stocking density. Several studies have examined the effects of density on the welfare of farmed fish, and have found it to be a source of chronic stress with commonly reported effects including reduced growth rates, alterations in the physical condition and health of fish, and the activation of stress responses. Such changes in the biological and physiological systems of fish are indicative of a reduced welfare status. However due to pronounced interspecies variations in behavioural and physiological requirements, the way in which stocking density affects various aspects of welfare in farmed fish is strongly species-specific, and in some cases life stage dependent. The combination of a range of indicators to assess the effect of density on fish welfare is the most reliable method to determine whether stocking density has a detrimental impact on the welfare of intensively farmed fish.