Environmental enrichment in captive juvenile thornback rays, Raja clavata (Linnaeus 1758)

•The study identified significant preferences for sand as a substrate compared to gravel or a bare tank, and significantly avoided black coloured sand over white or yellow sand.•The experiments involving group size showed significant increases in stereotypies with increasing numbers of individuals.•Rays spent more time resting in sand substrate and differed in type of resting in different depths of substrate.

There are few studies investigating captive conditions for commonly kept public aquaria species. Here the thornback ray (Raja clavata) was used to determine preferred captive conditions via choice tests and behavioural observations. Substrate type, substrate colour, substrate depth, group size and refuge use were all used to assess usage, number of stereotypic behaviours and activity in captive born rays. Sand was the preferred choice of substrate which also brought fewer surface breaking behaviours (a possible stereotypic behaviour) compared to gravel or bare tanks. Lighter colours of sand were preferred, as were deeper depths whilst increasing group size increased possible stereotypic behaviours. Type of resting behaviour (horizontal vs vertical) also differed within experiments − rays switched from horizontal to vertical resting, on the side of the tank when using gravelled versus sandy areas of the tank. The rays in this study appeared not to use refuges. Very few published studies have focused on what aquatic animals want, here we use preference tests, which are a useful way of determining what the animal wants, and can help aquarists provide the best conditions for captive thornback rays.