A conservative starting point

Seahorse tank-mate guide

Large seahorses here means tropical H. erectus, H. reidi and H. kuda. Individual fish and aquariums still vary.

Fish guide Coral guide Invertebrate guide

Green · generally compatibleYellow · use cautionRed · avoid

Dwarf seahorses are different.Because of their tiny size and live baby-brine feeding, the safest recommendation is a dedicated species tank with no fish tank mates.

Fish group	Large seahorses	Dwarf seahorses
Assessors & royal grammasUsually peaceful choices when given appropriate caves and territory.	Green · generally compatible	Red · avoid
CardinalfishGenerally calm, but watch feeding competition and adult size.	Green · generally compatible	Red · avoid
Dragonets & mandarinsPeaceful, deliberate feeders; best in a mature, pod-rich tank.	Green · generally compatible	Red · avoid
Firefish & dartfishPeaceful and generally unlikely to outcompete large seahorses.	Green · generally compatible	Red · avoid
PipefishSimilar pace, but disease transfer and specialized feeding make mixed housing advanced.	Green · generally compatible	Red · avoid
Small peaceful gobiesChoose calm species and avoid anything large enough to nip or swallow a seahorse.	Green · generally compatible	Red · avoid
AnthiasActive swimmers and feeders; large tanks and careful feeding are essential.	Yellow · use caution	Red · avoid
BlenniesSpecies vary; some, including Midas blennies, may compete strongly at meals.	Yellow · use caution	Red · avoid
ButterflyfishSpecies and individuals vary; most are active feeders and require expert judgment.	Yellow · use caution	Red · avoid
Chromis & other damselsChromis may be workable with caution; most damsels are territorial fin-nippers.	Yellow · use caution	Red · avoid
Clownfish (ocellaris & percula)Use only peaceful captive-bred individuals; they can be fast, competitive feeders.	Yellow · use caution	Red · avoid
Tangs & surgeonfishOnly a possible match in a spacious system with target feeding and a backup plan.	Yellow · use caution	Red · avoid
Wrasses (fairy & flasher)Among the milder wrasses, but still fast and competitive at feeding time.	Yellow · use caution	Red · avoid
AngelfishTerritorial behavior, nipping and feeding competition make them a poor match.	Red · avoid	Red · avoid
Clownfish (maroon, tomato & skunk)Tomato, maroon, skunk and similar clowns can become territorial or aggressive.	Red · avoid	Red · avoid
Groupers, morays & large predatorsAny fish capable of swallowing a seahorse must be excluded.	Red · avoid	Red · avoid
Lionfish, anglers & scorpionfishAmbush predators can swallow seahorses—even when they appear peaceful.	Red · avoid	Red · avoid
Triggers, puffers & cowfishAggression, biting and predatory behavior put seahorses at serious risk.	Red · avoid	Red · avoid
Wrasses (other)Many are too active, aggressive or predatory for a seahorse aquarium.	Red · avoid	Red · avoid

Before adding any tank mate: quarantine it, confirm the exact species, watch feeding competition closely and have a removal plan. New seahorse keepers will usually have the best start with a species-only aquarium.

Sources and methodology: adapted conservatively from Seahorse.com’s compatibility guidance ↗ and Alyssa’s Seahorse Savvy dwarf-safe collection ↗. A rating is guidance, not a guarantee.