List of fish suitable or unsuitable for cohabitation.
Small Characins (neon tetras, minor tetras, glowlight tetras, Nannostomus, pencilfish, phantom tetras, etc.). Suitable neighbors: all fish of this group, Anostomus, small barbs, Danios, White Cloud Mountain minnow, small American cichlids (Apistogramma, Aequidens, Laetacara curviceps), small African cichlids (Pelvicachromis pulcher, Pelvicachromis taeniatus), small livebearing toothcarps, small Labeo species (Epalzeorhynchos). Unsuitable neighbors: most cichlids, pike livebearer (Belonesox belizanus), large and predatory cyprinids and characins (Tetragonopterus, Acestrorhynchus, Congo tetra), large egg-laying toothcarps (Rivulus, Aphyosemion), gar pikes, eels, Pantodon, arowanas, large catfishes, Ctenopoma, bichirs, native fish species.
Small Cyprinids (barbs, Danio, White Cloud Mountain minnow, etc.). Suitable neighbors: all fish of this group, small characins, small American cichlids (Apistogramma, Laetacara curviceps), small African cichlids (Pelvicachromis pulcher, Pelvicachromis taeniatus), small livebearing toothcarps (guppies, platies, Limia), small Labeo species (Epalzeorhynchos). Unsuitable neighbors: most cichlids, pike livebearer, large and predatory cyprinids and characins, most egg-laying toothcarps, gar pikes, Pantodon, arowanas, large catfishes, Ctenopoma, bichirs, native fish species.
Large Characins from 10 cm in length (Congo tetras, silver dollars, Acestrorhynchus, Distichodus, etc.). Suitable neighbors: all fish of this group, large barbs, large danios, Chinese sucker, medium peaceful American cichlids (Aequidens, some Cichlasoma), large egg-laying toothcarps (Rivulus, Aphyosemion), large catfishes, Ctenopoma. Unsuitable neighbors: all small fish, all aggressive species including piranhas, African rift lake cichlids, big-mouthed fish (Acestrorhynchus and others with a similar body shape), bichirs, gar pikes, Pantodon, arowanas, native fish species.
Large Cyprinids from 10 cm in length (Tinfoil barb, arulius barb, giant danio, Labeo, Chinese sucker, etc.). Suitable neighbors: all fish of this group, large characins, medium peaceful American cichlids (blue acara, convict cichlid, meeki cichlid), large egg-laying toothcarps (Rivulus, Aphyosemion), Pantodon, non-aggressive catfishes, Ctenopoma. Unsuitable neighbors: all small fish, all aggressive species including piranhas, big-mouthed fish (for streamlined fish), African rift lake cichlids, bichirs, native fish species.
Goldfish, Koi carps. Suitable neighbors: all fish of this cold-water group of appropriate size (large and small specimens should not be mixed). Unsuitable neighbors: all other fish.
Discus. Suitable neighbors: only fish of this group and angelfish. Unsuitable neighbors: all other fish.
Small American and river African cichlids (Apistogramma, Laetacara curviceps, Pelvicachromis pulcher, Pelmatochromis, etc.). Suitable neighbors: fish of this group (many species should only be kept in pairs), many small and medium-sized characins and cyprinids. Unsuitable neighbors: predatory and aggressive fish.
African Rift Lake cichlids (Malawi and Tanganyika species). Suitable neighbors: fish of this group (many species should only be kept in pairs), large and medium Melanotaenia, Synodontis catfishes. Unsuitable neighbors: most other fish.
Large American cichlids (Astronotus, Cichlasoma, large Aequidens). Suitable neighbors: fish of this group (many species should only be kept in pairs), large and medium Melanotaenia, large catfishes, jewel cichlid (Hemichromis bimaculatus). Unsuitable neighbors: all small fish.
Arowanas. Suitable neighbors: large high-bodied fish; arowanas may also attack fish larger than themselves. Unsuitable neighbors: all smaller fish or fish with an elongated body.
Stress and its impact on fish health. What is fish stress?
Fish incompatibility parameters. Species-specific care features. 
