Compatibility Principles
Tank mate rules for arowanas: must be too large to swallow (over 1/3 of arowana body length), must occupy a different water column, must not nip fins, and must tolerate the same water parameters.
A 400+ gallon tank is the practical minimum for any arowana community. Smaller tanks force territory disputes.
Top Compatible Species
Datnoid (Datnioides species): mid-water, similar diet, peaceful with arowanas. The classic monster tank pairing.
Peacock bass (Cichla species): bottom-mid water, similar size and aggression level. Best in 500+ gallon.
Freshwater stingray (Potamotrygon species): bottom dweller, ignores arowana. Excellent companion in deep tanks.
Large plecos (Common pleco, sailfin pleco): bottom cleaners, ignored by arowana. Some risk of pleco sucking arowana slime coat at night — monitor.
Giant gourami (Osphronemus goramy): mid-water, gentle giant, peaceful with arowanas.
Risky Combinations
Oscar cichlid: territorial, will fight arowana for surface space. Frequent injuries.
Tinfoil barb school: arowana may pick them off one by one despite their size.
Bichir species: bottom dweller, generally peaceful, but some bichirs nip fins at night.
Knife fish: nocturnal, may stress arowana during night activity.
Never Mix
Two arowanas of any species (except mated breeding pairs in 800+ gallon tanks).
Aggressive cichlids (jaguar, dovii, red devil): will harass arowana to death.
Small tetras, rasboras, danios: lunch.
Small angelfish, discus, or rams: lunch.
Goldfish, rosy reds, koi: contain thiaminase, will damage arowana liver.
Introduction Protocol
Always introduce tank mates when the arowana is well-fed and not establishing territory. New tank mate first, arowana added later. Or rearrange décor before adding new fish to disrupt existing territory claims.
Have a backup tank ready. Even compatible species sometimes fail. A 75-gallon hospital tank can save a $500 datnoid that the arowana decides to harass.