Explore 95+ Fish That Start With O (Common Names)

Orchid Dottyback
© Minakryn Ruslan/Shutterstock.com

Written by Hannah Crawford

Published: August 9, 2023

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It never ceases to amaze us all the animals that there are in the world. Our oceans and waters make up 71% of the Earth’s surface. And when thinking about those numbers, it is no wonder there are some 3.5 trillion fish

Out of these vast numbers, we are alphabetizing each of the fish by their common names. And we have now reached the letter “O.” Let’s dive right in by looking at the ocean perch fish.

Ocean Perch (Sebastes alutus) Facts

Pacific Ocean Perch or Rockfish 2

The Pacific Ocean perch is also called



©Joe Belanger/Shutterstock.com

The ocean perch (Sebastes alutus) is a colorful-looking fish that is red or pink in appearance. They have scales along their body and spines along its back. These fish can be found in locations such as Asia, Eurasia, North America, and various oceans worldwide. 

Ocean perch fish live in a school-type environment. And because of this, they are no strangers to predators in the ocean. Sea creatures such as sablefish, halibut, sperm, whales, salmon, lingcod, seabirds, and rockfish will hunt these schools of fish and eat what they can. 

They will eat plankton to keep up with their small appearance. They weigh approximately four pounds and reach 20 inches long. 

Ocean Pout (Zoarces americanus) Facts

Ocean pout

The ocean pout possesses unique proteins in its blood that allow it to survive extremely cold temperatures.

©https://www.flickr.com/photos/dkeats/5532424100/ – Original / License

Not to be confused with the ocean perch, the ocean pout (Zoarces americanus) is a completely different fish. And as we could imagine, this fish has a “pout” like look on its face, just as its name suggests. 

The ocean pout of the family Zoarcidae can be found in various oceans worldwide. They can grow to be 46 inches long and weigh up to 14 pounds. As you may have thought, yes, this fish is a family member of the eelpout family, hence the family name Zoaricdae. Its lengthy appearance gives that one away.

Ocean pout’s eat a variety of invertebrates, crustaceans, and mollusks. They are hunted by larger prey such as seals, sculpins, and skates. 

Oilfish (Ruvettus pretiosus) Facts


Oilfish contain high levels of wax esters, which are indigestible to humans.


The oilfish (Ruvettus pretiosus) is a spiny-looking fellow that can be found in the deep sea about 2,600 feet below surface level. They can survive in both temperate and tropical waters. 

As carnivores, the oilfish will feast on squid, small fish, and crustaceans. Their growing appetite helps them to weigh as much as 140 pounds and reach 5-10 long. Due to this size, the oilfish’s predators are tunas and marlins. 

Opah (Lampris guttatus) Facts

Opah sunfish

Opah fish are nearly circular, with their bodies being nearly as wide as they are long.


Opahs  (Lampris guttatus) are vibrant-colored fish that are red, orange, and silver in appearance. Reaching 3-6 feet long, these lengthy sea creatures can also reach between 100-600 pounds. 

The opah can be found to reside in the Pacific Ocean, Indian Ocean, North Atlantic, and Mediterranean Sea. Their exact habitat location is largely dependent on the species of opahs. There are currently six species of opah. 

These carnivores are solitary hunters that will feast on squid, krill, and other small fish. Not too many fish in the ocean can compete with a 600-pound predator, so the only other known animal to hunt and eat opahs is the great white shark and the mako shark. 

Opaleye, Rudderfish (Girella nigricans)

Opaleye rudderfish

Opaleye rudderfish are omnivores.

©Podolnaya Elena/Shutterstock.com

The opaleye (Girella nigricans) of the family Kyphosidae are found in North America. While this fish might look rather bland in its picture, it can be yellow, blue, black, and green in appearance. These lengthy sea creatures can grow to 66 centimeters (26 inches) in length. 

They prey on sea animals such as crustaceans, worms, mollusks, and marine algae as well. They live in a group-like behavior known as a “school of fish.” 

A school of fish is defined by Science Focus as “A school is a group of the same fish species swimming together in synchrony; turning, twisting and forming sweeping, glinting shapes in the water.”

Orange Roughy (Hoplostethus atlanticus)

Orange Roughy

In the 1970s, fisheries stopped referring to orange roughy as slimeheads to make them more marketable as commercial fish.

©Brendan Lin/Shutterstock.com

Orange roughy (Hoplostethus atlanticus) fish have partially received this common name due to their orange-like appearance that they have. Although this is the main color we will see, the orange roughy scales can also look yellow, red, blue, black, and white as well. 

The orange roughy can weigh up to 15 pounds and grow to 30 inches long. Their behavior in the ocean is a group behavior in a school environment as well. They feast on zooplankton, crustaceans, shrimp, fish, and squid. 

There has been a very low decline in their population status, and because of this, the orange roughy is considered to be an endangered species. The biggest threat to their survival is overfishing. 

Orchid Dottyback (Pseudochromis fridmani) Facts

Orchid Dottyback

Unlike some other aquatic creatures who can change their colors on a whim, orchid dottybacks cannot. Their transformations can take several days to complete.


The orchid dottyback (Pseudochromis fridmani) is a brightly colored fish that is purple in appearance. While purple, this fish has the amazing ability to trick its prey and predators by camouflaging itself to its surroundings. 

They can be found in Australia, Asia, and in the Red Sea, to name a few locations. As carnivores, the orchid dottyback will feast on plankton, damselfish, and smaller docile fish.  

Oscar Fish (Astronotus ocellatus) Facts

Oscar Fish

Despite being a bit moody, Oscar fish are affectionate, often referred to as “river dogs.”

©weter 777/Shutterstock.com

Oscar fish (Astronotus ocellatus) of the family Cichlidae, interestingly enough, has teeth in its throat. If that didn’t creep you out enough, make sure to keep on reading about this fish. 

The oscar fish are found in habitats in Europe, North America, and South America. As such, they feast on freshwater clams, snails, shrimp, insect larvae, catfish, and insects. 

These incredibly fast fish can reach up to amazing speeds of 60 miles per hour, making them difficult prey to catch. However, it’s not impossible to catch them. Piranhas, waterbirds, reptiles, and humans are known to hunt and catch the oscar fish. 

Oyster Toadfish (Opsanus tau) Facts

close up of an oyster toadfish



can live up to 24 years in the wild.


The oyster toadfish (Opsanus tau) known for its toad-like appearance, is brown, black, and yellow in appearance. Only weighing between 3-5 pounds and reaching 8-17 inches, this rather small fish likes to stick to himself. 

The distinguishing factor about this fish is his big eyes that we see in the picture here!

Oyster toadfish prey on mollusks, crustaceans, squids, worms, and other fish. They are prey to sharks and other larger fish. 

Ozark Bass (Ambloplites constellatus) Facts

Ozark bass

The Ozark bass are mysterious fish and not much is known about them.

©cornysweaterman/CCBYSA4.0 – Original / License

Ozark bass (Ambloplites constellatus) live in very specific locations. They can only be found in North America in Arkansas and Missouri. Oddly enough, for only being found in specific locations, few things are known about their population status and natural predators. 

These funny-looking fish also go by the name “Google-eye” due to their large red eyes. The Ozark bass is a small little guy that weighs between 3.69 ounces and one pound. They will prey on minnows, crayfish, and insects. 

Largest Fish That Starts with the Letter “O”

Giant Oarfish

The Giant oarfish (Regalecus glesne) holds the Guinness Book of World Records for the longest bony fish in the world.

©Dotted Yeti/Shutterstock.com

While we have seen the below list of over 95+ fish, the oarfish (Regalecus glesne) holds the title for one of the largest fish that starts with the letter “O.” Not only is it one of the absolute largest fish, the giant oarfish is actually in the Guinness Book of World Records for the longest bony fish in the world

If you hop on over to the Guinness Book of World Records, you will see just how incredibly long and huge this fish is! They can grow to be 56 feet long and weigh up to 600 pounds. To give you an idea of how long that is, think of a semi-truck trailer. Those are typically 53 feet long. So, just imagine swimming in the ocean, and a semi-truck trailer comes right at you!

To keep up with their size, these carnivorous fish hunt and eat krill, shrimp, plankton, squid, and other small fish. Because of the little research available on these fish, it is difficult to understand all of their hunting patterns. What we do know is the oarfish are solitary hunters. 

It is assumed that these giant fish are hunted by large sea creatures such as the great white shark and orcas. Given how big oarfish are, it would make sense that their only predators are those who can compete with them in size. 

Now that we’ve shared the largest fish we could find with the letter “O,” we can now shift our focus to see the complete list of fish whose common names start with the letter “O” and their scientific names. 

Complete List of 95+ Fish That Starts with the Letter “O”

Common Name (Fish that start with “O”)Scientific Name (Fish that start with “O”)
OscarAstronotus ocellatus
Old Wife Enoplosus armatus
Ocean SunfishMola mola
Oceanic Whitetip Shark Carcharhinus longimanus
Olive Flounder Paralichthys olivaceus
Obese Synodontis Synodontis obesus
One lined pencilfish Nannostomus unifasciatus
Olga coryCorydoras simulatus
Oneline tetraNannaethiops unitaeniatus
Orange chromideEtroplus maculatus
Okefenokee pygmy sunfish Elassoma okefenokee
Ornate rainbowfish Rhadinocentrus ornatus
Ocellated puffer fish Leiodon cutcutia
One-gilled swamp eel Ophisternon bengalense
Orangespotted sunfish Lepomis humilis
Octozona barb Eirmotus octozona
Ornate pimelodus Pimelodus ornatus
Ocellated freshwater stingray Potamotrygon motoro
Otorongo rayPotamotrygon castexi
Orinoco peacock bassCichla orinocensis
Onespot barbPuntius terio
Ornate tetraHyphessobrycon bentosi
Oil catfishCentromochlus perugiae
Odynea pimelodid catfishPimelodella odynea
Orinoco angelfishPterophyllum altum
Okavango tilapiaTilapia ruweti
Oaxaca cichlidVieja zonata
Odo cichlid Nandopsis haitiensis
Orangethroat darterEtheostoma spectabile
Ocellated snakeheadChanna pleurophthalma
Ornate bichirPolypterus ornatipinnis
Ocellated bushfishCtenopoma muriei
Oxyrhynchus tube-snouted ghost knifefishSternarchorhynchus oxyrhynchus
Orange-finned danioDanio kyathit
Odessa barbPuntius padamya
Orange fin merry widowPhallichthys amates
One-lined African characinNannaethiops unitaeniatus
Opaline gouramiTrichogaster trichopterus
One spot bettaBetta unimaculata
Obscure snakeheadParachanna obscura
Ocellate river stingrayPotamotrygon motoro
Orange-lined reef bassletAkysis vespa
One-spot butterflyfish Chaetodon unimaculatus
Okinawa gobyGobiodon okinawae
Ornate surgeonfishAcanthurus dussumieri
One-stripe anthiasPseudanthias fasciatus
Orange lined reef bassletLiopropoma swalesi
Orange diamond gobyValenciennea puellaris
Oxeye herringMegalops cyprinoides
Orange shoulder tangAcanthurus olivaceus
Orange blotch surgeonfishAcanthurus olivaceus
Orange skunk clownfishAmphiprion akallopisos
Orbicular batfishPlatax orbicularis
One spot foxfaceSiganus unimaculatus
Orchid dottybackPseudochromis fridmani
Oriole angelCentropyge bicolor
Ocellated lionfishDendrochirus biocellatus
Ornate wrasseThalassoma pavo
Orange-lined triggerfishBalistapus undulatus
Oblong blowfishTakifugu oblongus
Orange spotted sleeper gobyValenciennea puellaris
Orange lined cardinalfishApogon cyanosoma
Orange anemonefishAmphiprion sandaracinos
Oualan forktail blennyMeiacanthus oualanensis
Ocellated dragonetSynchiropus ocellatus
Ocellaris clownfishAmphiprion ocellaris
Old gloryAmblygobius rainfordi
Orange firefishNemateleotris magnifica
Orange spotted shrimp gobyAmblygobius guttata
Orange sea perch Pseudanthias squamipinnis
Orbiculate cardinalfishSphaermia orbicularis
Orangebanded stingfishChoridactylus multibarbus
Oblique-lined dottybackCypho purpurascens
Orange spotted gobyAmblyeleotris guttata
Orangetip bristletooth Ctenochaetus tominiensis
OrandaCarassius auratus auratus
Otocinclus cat Otocinclus vestitus
Ornate wrasseThalassoma pavo
Orangespine unicornfishNaso lituratus
Orange fin barbBarbus eutaenia
Onespot squeakerSynodontis notata
Orange clownfishAmphiprion percula
Orange spotted spinefootSiganus guttatus
Ornate butterflyfishChaetodon ornatissimus
Ocean PerchSebastes alutus
Ocean PoutZoarces americanus
Ocean WhitefishCaulolatilus princeps
OpahLampris guttatus
Opaleye (Rudderfish)Girella nigricans
Orange RoughyHoplostethus atlanticus
Oscar FishAstronotus ocellatus
Oyster ToadfishOpsanus tau
Ozark Bass  Ambloplites constellatus

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About the Author

Hannah Crawford is a writer at A-Z Animals where she focuses on reptiles, mammals, and locations in Africa. Hannah has been researching and writing about animals and various countries for over eight years. She holds a Bachelors Degree in Communication\Performance Studies from Pensacola Christian College, which she earned in 2015. Hannah is a resident in Florida, and enjoys theatre, poetry, and growing her fish tank.

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