Rays are among the top predators in the ecosystems they populate in nature and are unsafe to keep with most other species. Conversely they also seem to prefer a quiet life and will often fail to thrive when kept alongside very aggressive or territorial companions. The best tankmates are large enough not to be eaten, peaceful and ideally occupy the upper parts of the tank. Some cichlids, such as Heros or Geophagus species work well, as do many bigger characins and cyprinids. Plenty of enthusiasts keep Asian or South American arowana with their rays, and in a roomy tank this can be a very striking combination. Other suitable options include Cichla or Datnioides spp., and in a tank with a very large footprint other bottom dwellers such as bichirs or Pimelodid catfish (Brachyplatystoma tigrinum is a popular albeit expensive choice). Obviously all these species grow to an impressive size so tank volume should be the primary consideration before any choices are made.