The longsnout seahorse Hippocampus reidi is highly valued in the ornamental aquarium trade, being intended for public and private aquariums due to its attractive appearance and interesting behaviour. H. reidi is considered a social species, as in its natural habitat individuals are typically found in pairs or groups of varying sizes. However, they are often kept in isolation in aquariums or for research purposes.This study aimed to evaluate the behaviour and food intake of seahorses under two captive conditions: physical social isolation and group housing.
Twenty seahorses were maintained in 300-L aquariums fitted with removable glass dividers, creating four individual 75-L compartments for isolation. Significant differences (p<0.05) emerged between the two conditions: feeding duration was markedly longer in the group setting. Moreover, both feeding frequency and holding behaviour occurred more often in groups. Food consumption dropped by 50% when seahorses were placed in physical contact isolation compared to group housing. Some individuals attempted to reunite by moving through the glass partitions.
Additionally, the animals’ coloration shifted rapidly from yellow to dark brown, accompanied by increased opercular beating—both indicators of stress. These findings show that short-term physical contact isolation induces stress-related behavioural changes and reduces food intake in H. reidi. Prolonged isolation could negatively affect the welfare and survival of the species, with potentially lethal consequences. For this reason, seahorses should be kept in groups in both aquarium and research settings.
Acknowledgments: This research was partially funded by the Coordination for the Improvement of Higher Education Personnel (CAPES, Brazil) – Finance Code 001, and by the Brazilian National Council for Scientific and Technological Development (CNPq, Brazil), which provided a grant to M.Y. Tsuzuki (310843/2021-9) and financial support for the research (Process 407610/2021-9