Fish Species Starting with O
Browse all aquarium fish species with scientific 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 are seeking efficient algae eaters or unique additions to your tank, this section offers valuable insights into these captivating species.
3 species found
Golden otocinclus
Otocinclus affinis
Otocinclus affinis is a small South American suckermouth catfish prized for grazing soft algae and biofilm on plants, glass, and décor. It has a slender body with a dark lateral stripe and a pale underside, and it is best kept in groups where it feels secure. Although peaceful, it can be delicate when newly imported and does best in mature, well-oxygenated aquariums with plenty of natural growth to graze.
Common otocinclus
Otocinclus vittatus
O. vittatus is that tiny little "oto" you see plastered to plant leaves and the glass, just quietly vacuuming up soft algae and biofilm all day. The big trick with them is they're amazing grazers, but they can absolutely run out of food in a too-clean/new tank, so you've got to plan on supplementing with algae wafers/blanched veg.
Harlequin filefish
Oxymonacanthus longirostris
This is that super-cool orange-spotted, long-snouted filefish that hangs tight in branching Acropora like it's part of the coral. In the wild it's basically an Acropora-polyp specialist and usually lives in pairs, which is exactly why it's so tricky in home aquariums unless you're ready for the feeding challenge.