Impact of environmental enrichment and social group size in the aggressiveness and foraging activity of Serrapinnus notomelas

Abstract

Fish are widely used in scientific research, and many species are bred for ornamental purposes and human consumption. Despite the large number of fish kept in captivity, research on the welfare of these animals has only recently intensified. One commonly used method for improving fish welfare is environmental enrichment, and the issue of animal density is central to this debate. Both enrichment and variation in fish density may have different impacts on the welfare of fish, which will depend on the biology of each species. In this study, we verified if environmental enrichment reduced aggressiveness and increased foraging activity in Serrapinnus notomelas in captivity. S. notomelas is a Neotropical characin commonly used in the aquarium trade. It has also been reared in captivity for scientific research purposes. However, studies on the welfare of S. notomelas in captivity are still lacking. We measured the aggressiveness and foraging activity of fishes in aquariums with different levels of enrichment (enriched and highly enriched), in comparison to an enrichment-free aquarium. The same behavioral aspects were quantified in groups of six and 12 individuals since it is known that group size influences these characteristics in shoal fishes. We found no influence of environmental enrichment on the species’ aggressiveness. However, fish housed in highly enriched aquariums increased their foraging activity to levels similar to fish housed in enrichment-free aquariums. We also found no influence of group size on the aggressiveness of individuals. However, increased group size had a positive effect on foraging activity, therefore we suggest housing S. notomelas with a minimum of 12 individuals. Results reinforce the need for species-specific investigation regarding both enrichment and shoal size to improve the welfare of captive fishes. We also encourage future studies on the effects of different enrichment levels, because we found that the level of enrichment affected the welfare of S. notomelas.