Fish That Start With O
Browse all aquarium fish species with common names beginning with "O". Each profile includes care requirements, water parameters, tank size recommendations, and compatibility information for freshwater, marine, and brackish species.
The letter 'O' in our species index features a diverse range of aquarium fish, including popular community members like the Golden otocinclus (Otocinclus affinis) and the Common otocinclus (Otocinclus vittatus), as well as the intriguing Harlequin filefish (Oxymonacanthus longirostris). Whether you're looking for efficient algae eaters or unique tank additions, this section offers valuable insights into these captivating species.
Ocean surgeonfish
Acanthurus tractus
Acanthurus tractus is a Western Atlantic tang that cruises reefs in little groups, spending most of the day mowing down benthic algae. It is got that classic surgeonfish attitude (and the tail scalpel to match), so it likes real swimming room and steady, clean reef conditions.
Ocellaris clownfish
Amphiprion ocellaris
Ocellaris clowns are that classic orange clownfish look-three white bars, a little black edging, and a ton of attitude packed into a small fish. They'll "pick a spot" in the tank (often a corner or a coral) and do that cute hover-wiggle thing, and a bonded pair will usually settle in fast and act like they own the place.
Oluolus hatchetfish
Polyipnus oluolus
Polyipnus oluolus is a tiny deepwater marine hatchetfish from the Marshall Islands that lives out in the open ocean and uses little light organs (photophores) on its body for camouflage and signaling in the dim water. It is super cool from a biology standpoint, but its pelagic deep-sea lifestyle makes it basically a non-aquarium species for normal hobby setups.
One-spot Jupiaba tetra
Jupiaba mucronata
Jupiaba mucronata is a little Guyana characin that tops out around 4 cm SL, and it fits that classic "busy, always on the move" tetra vibe. Its claim to fame in a lot of checklists is the single prominent shoulder (humeral) spot, and it does best when you lean into a roomy, current-friendly setup and keep it in a proper group.
Orange bellowfish
Notopogon fernandezianus
Notopogon fernandezianus is the orange bellowfish, a weird little deepwater "trumpet fish" with a long snout and a tall, humped body. It lives way down on the continental shelf and slope (roughly 150-580 m), so its natural world is cold, dark, and high-pressure - basically the opposite of a home aquarium. Super cool to look at, but not a realistic species to keep alive long-term in normal hobby setups.
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Orange chromide
Pseudetroplus maculatus (syn. Etroplus maculatus)
This is that cute little Indian/Sri Lankan cichlid with the big black "shoulder" spot and a warm gold/orange glow when it's happy. It'll do the classic cichlid thing where it gets a bit pushy when breeding, but most of the time it's pretty chill-especially if you keep a small group. Super cool bonus: the parents actively tend the eggs and fry, and the babies even graze on the parents' skin mucus for a bit.
Orange-spotted toadfish
Torquigener hypselogeneion
This is a small Indo-west Pacific puffer that hangs around sandy flats and estuaries, and it will literally bury itself in the sand to nap with just the eyes sticking out. Its cheek bars and orange-yellow spotting make it look like a little camo tank. Cool fish to read about, but its pufferfish teeth and potential toxicity mean its not a typical community-aquarium pet.