Freshwater aquarium fish: O
All freshwater fish whose common name starts with O, in alphabetical order. Each card links to its care guide.
67 species and 6 varieties
Oaxaca vieja
Vieja zonata
Freshwater9.8 in (25 cm) · 132 gal (500 L)75–84°F (24–29°C)
OB peacock cichlid
Aulonocara hybrid
Freshwater5.9 in (15 cm) · 63 gal (240 L)75–82°F (24–28°C)2 varietiesObscura betta
Betta obscura
Freshwater2.7 in (6.9 cm) · 20 gal (75 L)72–81°F (22–27°C)
Ocellate river stingray
Potamotrygon motoro
Freshwater19.7 in (50 cm) · 264 gal (1,000 L)75–82°F (24–28°C)
Ocellated kribensis
Pelvicachromis subocellatus
Freshwater3.9 in (10 cm) · 21 gal (80 L)75–81°F (24–27°C)
Ocellated puffer
Leiodon cutcutia
Freshwater5.9 in (15 cm) · 29 gal (110 L)75–82°F (24–28°C)
Ocellated snakehead
Channa pleurophthalma
Freshwater15.7 in (40 cm) · 70 gal (265 L)75–82°F (24–28°C)
Ocellated squeaker
Synodontis ocellifer
Freshwater7.9 in (20 cm) · 53 gal (200 L)73–81°F (23–27°C)
Odessa barb
Pethia padamya
Freshwater1.8 in (4.5 cm) · 20 gal (75 L)61–77°F (16–25°C)
Odo cichlid
Nandopsis haitiensis
Freshwater10.2 in (26 cm) · 132 gal (500 L)75–84°F (24–29°C)
Ogilbie's osteobrama
Rohtee ogilbii
Freshwater7.9 in (20 cm) · 66 gal (250 L)68–81°F (20–27°C)
Ogilby's rainbowfish
Melanotaenia ogilbyi
Freshwater3.1 in (8 cm) · 29 gal (110 L)75–84°F (24–29°C)
Ogilvie's lizard loach
Homaloptera ogilviei
Freshwater2.4 in (6 cm) · 20 gal (75 L)70–79°F (21–26°C)
Ogowe killifish
Aphyosemion ogoense
Freshwater2 in (5 cm) · 11 gal (40 L)64–73°F (18–23°C)
Oiapoque cory
Hoplisoma oiapoquense
Freshwater2.2 in (5.5 cm) · 20 gal (75 L)73–79°F (23–26°C)
Oil catfish
Duringlanis perugiae
Freshwater2.4 in (6 cm) · 15 gal (55 L)75–82°F (24–28°C)Omega betta
Betta omega
Freshwater3.2 in (8.1 cm) · 24 gal (90 L)73–81°F (23–27°C)
Ommation whiptail
Rhadinoloricaria ommation
Freshwater5.7 in (14.5 cm) · 40 gal (150 L)73–82°F (23–28°C)
Ompok catfish
Ompok pabda
Freshwater11.8 in (30 cm) · 106 gal (400 L)73–81°F (23–27°C)
One-lined pencilfish
Nannostomus unifasciatus
Freshwater1.6 in (4 cm) · 17 gal (65 L)73–82°F (23–28°C)
One-spot betta
Betta unimaculata
Freshwater4.5 in (11.5 cm) · 29 gal (110 L)70–79°F (21–26°C)
One-spot synodontis
Synodontis notatus
Freshwater9.8 in (25 cm) · 53 gal (200 L)72–81°F (22–27°C)
One-stripe spiny eel
Macrognathus aral
Freshwater23.6 in (60 cm) · 119 gal (450 L)73–82°F (23–28°C)
Onespot barb
Puntius terio
Freshwater3.1 in (8 cm) · 20 gal (75 L)68–79°F (20–26°C)
Opal licorice gourami
Parosphromenus opallios
Freshwater1.2 in (3 cm) · 5 gal (20 L)72–81°F (22–27°C)
Opal spot pleco
Scobinancistrus raonii
Freshwater6.3 in (16 cm) · 79 gal (300 L)81–88°F (27–31°C)
Opossum pipefish
Microphis brachyurus
FreshwaterBrackish8.7 in (22 cm) · 32 gal (120 L)75–82°F (24–28°C)
Orange chromide
Etroplus maculatus
FreshwaterBrackish3.9 in (10 cm) · 55 gal (210 L)68–82°F (20–28°C)
Orange Congo tetra
Phenacogrammus aurantiacus
Freshwater3.9 in (10 cm) · 42 gal (160 L)73–81°F (23–27°C)
Orange fin goby
Stiphodon maculidorsalis
Freshwater2.2 in (5.5 cm) · 14 gal (54 L)73–81°F (23–27°C)
Orange hatchet danio
Laubuka dadiburjori
Freshwater1.2 in (3 cm) · 13 gal (50 L)68–75°F (20–24°C)
Orange marble bee catfish
Akysis longifilis
Freshwater2.4 in (6 cm) · 14 gal (54 L)72–79°F (22–26°C)
Orange seam pleco
Hemiancistrus guahiborum
Freshwater5.5 in (14 cm) · 66 gal (250 L)77–84°F (25–29°C)
Orange-finned danio
Danio kyathit
Freshwater2 in (5 cm) · 20 gal (75 L)68–79°F (20–26°C)
Orange-spotted snakehead
Channa aurantimaculata
Freshwater15.7 in (40 cm) · 119 gal (450 L)59–77°F (15–25°C)
Orangethroat darter
Etheostoma spectabile
Freshwater2.8 in (7 cm) · 25 gal (95 L)59–68°F (15–20°C)
Orces's cory
Corydoras orcesi
Freshwater2.4 in (6 cm) · 20 gal (75 L)73–81°F (23–27°C)
Orientalis squeaker
Synodontis orientalis
Freshwater4.3 in (11 cm) · 42 gal (160 L)73–81°F (23–27°C)
Orinoco angel pleco (L201)
Hypancistrus sp. L201
Freshwater5.9 in (15 cm) · 30 gal (115 L)79–86°F (26–30°C)
Orinoco cupid cichlid
Biotodoma wavrini
Freshwater4.7 in (12 cm) · 66 gal (250 L)77–84°F (25–29°C)
Orinoco dolphin catfish
Ageneiosus magoi
Freshwater7.1 in (18 cm) · 106 gal (400 L)73–82°F (23–28°C)
Orinoco dwarf pleco
Peckoltia lineola
Freshwater4.3 in (11 cm) · 29 gal (110 L)77–84°F (25–29°C)
Orinoco flagtail prochilodus
Semaprochilodus laticeps
Freshwater17.3 in (44 cm) · 264 gal (1,000 L)73–82°F (23–28°C)
Orinoco peacock bass
Cichla orinocensis
Freshwater24.4 in (62 cm) · 528 gal (2,000 L)77–86°F (25–30°C)
Orinoco peckoltia
Peckoltia lujani
Freshwater3.5 in (9 cm) · 29 gal (110 L)77–84°F (25–29°C)
Orinoco polka-dot pleco
Hypancistrus contradens
Freshwater4.7 in (12 cm) · 42 gal (160 L)79–86°F (26–30°C)
Orinoco spotted raphael
Agamyxis albomaculatus
Freshwater5.9 in (15 cm) · 40 gal (150 L)73–82°F (23–28°C)
Orinoco talking catfish
Orinocodoras eigenmanni
Freshwater7.9 in (20 cm) · 70 gal (265 L)73–82°F (23–28°C)
Ornate bichir
Polypterus ornatipinnis
Freshwater21.7 in (55 cm) · 172 gal (650 L)77–82°F (25–28°C)
Ornate bushfish
Microctenopoma ansorgii
Freshwater3.1 in (8 cm) · 20 gal (75 L)73–81°F (23–27°C)
Ornate cory
Brochis ornata
Freshwater2.8 in (7 cm) · 24 gal (90 L)72–79°F (22–26°C)
Ornate garra
Garra ornata
Freshwater4.3 in (11 cm) · 29 gal (110 L)72–81°F (22–27°C)
Ornate hap
Protomelas ornatus
Freshwater7.2 in (18.2 cm) · 106 gal (400 L)75–82°F (24–28°C)
Ornate paradisefish
Malpulutta kretseri
Freshwater2 in (5 cm) · 12 gal (45 L)72–82°F (22–28°C)
Ornate pimelodus
Pimelodus ornatus
Freshwater12.2 in (31 cm) · 65 gal (245 L)75–82°F (24–28°C)
Ornate rainbowfish
Rhadinocentrus ornatus
Freshwater2.4 in (6 cm) · 20 gal (75 L)64–82°F (18–28°C)
Ornate shell dweller
Lamprologus ornatipinnis
Freshwater2.4 in (6 cm) · 16 gal (60 L)75–81°F (24–27°C)
Ornate stone loach
Nemacheilus ornatus
Freshwater2 in (5 cm) · 20 gal (75 L)72–79°F (22–26°C)
Ornate tetra
Hyphessobrycon bentosi
Freshwater1.8 in (4.5 cm) · 20 gal (75 L)72–82°F (22–28°C)
Ornate-tail Borneo sucker
Gastromyzon ornaticauda
Freshwater3.3 in (8.4 cm) · 24 gal (90 L)68–77°F (20–25°C)
Ornate-tail licorice gourami
Parosphromenus ornaticauda
Freshwater0.9 in (2.4 cm) · 5 gal (20 L)72–81°F (22–27°C)
Ortega's cory
Hoplisoma ortegai
Freshwater2 in (5 cm) · 16 gal (60 L)73–81°F (23–27°C)
Ortega's dwarf cichlid
Apistogramma ortegai
Freshwater2.6 in (6.5 cm) · 16 gal (60 L)75–82°F (24–28°C)
Oscar
Astronotus ocellatus
Freshwater13.8 in (35 cm) · 95 gal (360 L)68–82°F (20–28°C)4 varieties
Ourastigma cory
Corydoras ourastigma
Freshwater2.6 in (6.5 cm) · 20 gal (75 L)75–82°F (24–28°C)
Owroewefi guianacara
Guianacara owroewefi
Freshwater5.1 in (13 cm) · 66 gal (250 L)77–84°F (25–29°C)
Oxyrhynchus hap
Hemitilapia oxyrhynchus
Freshwater7.9 in (20 cm) · 119 gal (450 L)75–81°F (24–27°C)
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