Fish Tankmates That Actually Get Along — and Pairings to Avoid

Both species are small, peaceful mid-water swimmers that prefer soft, slightly acidic water (pH 6.5–7.0) and temperatures between 72°F and 78°F. They pose no threat to each other and create a visually dynamic tank when kept in schools of six or more each. Neither species is territorial, and their similar dietary needs — small flakes and micro-pellets — make feeding straightforward.

Avoid pairing either with larger, nippy species like tiger barbs, which will target their flowing fins and smaller bodies.

Corydoras are armored, bottom-dwelling catfish that spend most of their time sifting the substrate for food scraps. They occupy a completely different swimming zone than most community fish, so competition and aggression are minimal. They are compatible with tetras, rasboras, guppies, mollies, and many livebearers, as long as water temperature falls within the 72°F–78°F range they prefer.

Keep corydoras in groups of at least four to six — they are social fish that exhibit stress and reduced activity when kept alone. Avoid housing them with aggressive bottom-dwellers like larger loaches that may bully them at feeding time.

Bettas are frequently misrepresented as community fish. Male bettas are highly territorial toward other males and will attack any fish that resembles them — brightly colored, long-finned species are especially at risk. However, bettas can coexist peacefully with mystery snails, nerite snails, and certain bottom-dwellers like pygmy corydoras in tanks of at least ten gallons with adequate cover.

Avoid pairing bettas with guppies (whose flowing tails trigger aggression), tiger barbs (known fin-nippers), or any other betta. Female bettas may coexist in a carefully managed sorority, but this setup requires specific conditions and close observation.

Goldfish are coldwater fish that thrive between 65°F and 72°F and produce significantly more ammonia waste than most tropical species. Pairing them with tropical fish creates an impossible compromise: the water temperature that suits goldfish chills tropical fish into immune suppression, while warmer settings stress goldfish and accelerate disease. Our article on goldfish biology explores why these fish have far more specific needs than their reputation suggests.

Within a coldwater setup, goldfish generally coexist well with other goldfish of similar size. White cloud mountain minnows are one of the few small species that tolerate similar temperatures, though goldfish may attempt to eat very small tankmates as they grow.

African cichlids from Lake Malawi and Lake Tanganyika are aggressive, territorial, and active — qualities that make them incompatible with nearly all peaceful community fish. They do, however, often coexist with other African cichlids of similar size and aggression level when the tank is large enough (75 gallons or more), heavily stocked to distribute aggression, and structured with caves and rockwork to break sightlines.

The key risk is keeping too few fish: dominant individuals will single out and relentlessly harass subordinates. Mixing cichlids from different African rift lakes is generally not recommended, as their water chemistry preferences differ meaningfully.

Some combinations appear frequently in pet stores but are consistently problematic:

• Oscar cichlids + small tetras or guppies: Oscars are large, predatory cichlids. Any fish that fits in their mouth will eventually be eaten.
• Red-tailed sharks + other bottom-dwellers: Red-tailed sharks are highly territorial on the substrate and will aggressively chase corydoras, loaches, and other species that share their zone.
• Fancy goldfish + common goldfish: Common goldfish are faster swimmers and more competitive feeders, often outcompeting fancy varieties for food, which leads to malnourishment in the slower fish.
• Tiger barbs in small groups: Tiger barbs kept in groups of fewer than six turn their fin-nipping aggression on tankmates rather than each other. They need larger schools to redirect that energy internally.