Male betta splendons, also called Siamese fighting fish, viciously attack other male bettas or any fish resembling another male betta. Under certain conditions, your male betta can live with other fish species. A 10- or 20-gallon tank works best for keeping bettas with other fish, as bettas feel uncomfortable in large tanks where they instinctively try to defend their whole territory. Peaceful, fast-moving fish without flowing fins have the best chance of surviving life with a male betta.
Bettas often ignore tropical minnow-type fish which move quickly and have no colorful, flowing fins, such as cherry barbs. The California Betta Society recommends neon tetras and mollies. Aquarist Josh Day agrees, and adds swordtails to the list. Other peaceful, tropical minnow fish which may work with male bettas include cardinal tetras, glowlight tetras, dwarf rasporas and golden barbs.
Catfish-type, bottom-dwelling scavengers may live successfully with a male betta. For example, the common plecostomus or the cory catfish may live with male bettas without issue.
According to the website Healthy Betta, some aquarists have had luck housing male bettas with zebra danios. However, the California Betta Society notes that zebra danios notoriously nip the fins of other fish, and may pose a danger to your betta.
Fish to Avoid
Some fish will almost never survive living with a male betta. For example, goldfish, who are cold-water fish, do not belong with tropical bettas. Angel fish and discus will definitely get attacked by male bettas who mistake their long fins for those of another male betta. Aggressive, territorial cichlids should not live with bettas. Rainbow sharks and bettas will likely fight each other. A male betta and a female betta will fight if one or the other is not willing to spawn.