Influence of social enrichment on transport stress in fish: a behavioural approach

Ornamental fishes are among the most commonly owned companion animals in the world, however, the transportation process during acquisition can result in fishes being exposed to biotic and abiotic conditions which compromise welfare. While many studies have considered methods of improving welfare for food fishes through physical and social enrichment, few have considered how to improve welfare of ornamental fishes post-transport. We investigated whether (i) being introduced into an empty tank, a tank with resident conspecifics (variatus platys; Xiphophorus variatus), or a tank with resident heterospecifics (common mollies; P. sphenops) and (ii) being able to see resident fish in an adjacent tank affected stress-associated behaviour post-transport. Videos of variatus platys being introduced to their treatment tanks were taken immediately on release following transport, and at 1, 24, 72, 120 and 168 h after release. Behaviours, including biting, chasing, erratic movement and time spent immobile, were analysed across all time points. Latency to forage was analysed immediately upon release post-transport only. The social composition of the tanks that the variatus platys were placed in influenced the majority of behaviours analysed, however visual cues only had a significant effect on chasing behaviour at 168 h post release and on biting behaviours of resident fish towards transported fish. Fish placed in tanks with resident conspecifics exhibited significantly more agonistic behaviours than those introduced into empty tanks or with resident heterospecifics. Variatus platys introduced into tanks with resident conspecifics had shorter foraging latencies. It is clear that tank composition post-transport has an effect on behaviour of ornamental fishes and represents a way in which retailers can implement welfare improvements. •Investigated optimal tank social compositions to promote recovery from transport in ornamental fishes.•Placing fish in empty tanks aids behavioural recovery e.g. decreased foraging latency and aggression.•Manipulation of tank composition could be used by retailers to refine welfare.•Highlights the importance of species-specific social dynamics when alleviating stress effects.