Betta cohabitation is one of the most-debated aquarium topics. The safe answer: most bettas thrive solo. Multiple males - never: male Betta splendens will fight to the death in any tank size, no exception. Even sight of another male through dividers triggers chronic stress. Female sorority (advanced setup only): 5+ females in a heavily-planted 20-gallon long minimum. Smaller groups cause one fish to be bullied to death. Introduce all females simultaneously, never add to existing group. Each female needs her own territory + escape route + multiple sight breaks. Even successful sororities can fail without warning. Failure rate: 30-50%. Male + female (breeding setup only): separate tanks normally; combined briefly in a 10g+ breeding tank with hides. Female removed after spawn. Never permanent cohabitation. Wild bettas (B. imbellis, B. smaragdina, B. mahachaiensis): some species can be kept in pairs/trios with extreme caution + huge tanks. Not for beginners. Splendens with other species: peaceful tankmates only - corydoras (larger species), kuhli loaches, ember tetras, snails, shrimp (50/50 - some bettas eat shrimp). Avoid: fin nippers (tiger barbs, serpae tetras), aggressive fish, brightly-colored males the betta sees as rivals. Recommendation: 1 male betta in a 5g+ planted tank with snails + perhaps 5-10 amano shrimp. Most peaceful long-term setup.
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