Last update: November 14, 2022

75+ Popular Fish That Start With O

Amongst all the seas, oceans, rivers, and bodies of water on our planet, the sheer amount of fish many of us haven’t heard of is astounding. Of the 75+ popular fish that start with O, there are likely some you didn’t know exist. 

There are thousands upon thousands of fish in the sea, many of whom have interesting names and even more interesting characteristics. Some of the fish that made it on the 75+ popular fish that start with O, like the oarfish or the olive flounder, are names that are somewhat recognizable.

Others are ones that you might not be familiar with, and others have intriguing and somewhat humorous names. 

Additionally, many of these fish have similar names, but they are all different and live all around the world. These fish are some you might be able to bring home as you build a new aquarium, and others you’ll either only see in pictures or perhaps when going scuba diving. 

75+ Popular Fish That Start With O 

Fish are so fascinating to learn about, as each have their own personalities, appearances, and preferences. This is especially true when you learn about all the different fish with names starting with the letter O.

Some enjoy fresh water, some thrive in salt water, while others are typically found in more tropical regions. 

Also read:

Our Top 7 Fish That Start With O 

Below are some of the most well-known fish that have names starting with the letter O. Their names are also accompanied by their Latin name, as well as some compelling information about why these fish are worth knowing about. 

1. Oscar (Astronotus ocellatus)

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The oscar is a freshwater cichlid that many aquarium enthusiasts enjoy having at home, though they aren’t the best option for someone new to fish care.

Those who own an oscar know that they are quite a quirky fish with a fun personality, making their striking visage a lot of fun to watch swimming about in a tank. 

The oscar fish is a carnivore who enjoys a pretty diverse diet mixed with small fish, insects, and will even eat some plants.

On occasion, this particular fish can show some territorial tendencies, but this shouldn’t be an issue if you have them in a decent sized aquarium. When cared for well, an oscar fish can live up to 20 years. 

2. Old Wife (Enoplosus armatus)

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The old wife fish is an Australian fish with shining silver and black vertical striping and pronounced dorsal fins.

This very gorgeous fish has been discovered in fossil form, which has led to the discovery that it has lived in Australian waters for over 50 million years. As of now, they tend to swim around various coastal reefs amongst the continent. 

The story behind this fish’s interesting name is actually quite peculiar. It’s said that when this fish is caught, they make a noise that sounds almost exactly like they’re saying “old wife,” and they make this noise by grinding their teeth. 

3. Oarfish (Regalecidae)

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An oarfish looks somewhat like an eel, but is substantially larger; these massive fish can reach up to 26 feet long. The oarfish tends to make news when it comes up to shore, but sadly, they usually only do this when sick.

Otherwise, these fish are very mysterious and, while they can live in waters in different climates, they tend to dwell at much lower levels. 

Believe it or not, it’s assumed that when people have reported various sightings of legendary or mythical creatures swimming around, they might have actually seen an oarfish.

Given how long this fish is and how it looks when it swims, it’s not surprising people might think it’s of mythical origins. 

4. Ocean Sunfish (Mola mola)

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The ocean sunfish is a very large, very unique kind of fish that actually resembles a sun when it’s still a fry. When they grow, they are a fairly bulbous fish with a fin on their head and chubby cheeks.

Unlike most other fish, the ocean sunfish actually has a skeleton made of bone tissue. When full grown, this fish can weigh as much as 5000 to 6000 pounds. 

The ocean sunfish also enjoys sunbathing, and if you’re lucky, you can sometimes spot these fish laying on their side at the top of the sea and catching some rays. Their delicacy of choice is a jellyfish, but they are known not to be especially picky eaters. 

5. Oceanic Whitetip Shark (Carcharhinus longimanus)

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Sharks aren’t always appreciated for how entrancing they are due to common misunderstandings for how dangerous they are.

That said, you don’t want to be stuck in the water with one of these, notoriously nicknamed the shipwreck shark. Otherwise, this is a docile and fairly sedentary shark that enjoys warm water. 

The oceanic whitetip shark is found in three of the five major oceans, and they enjoy fairly chilly waters. It’s not likely one will ever encounter one of these sharks as they tend not to come close to the shore very often, if at all. 

6. Olive Flounder (Paralichthys olivaceus)

An olive flounder is one of those fish with a very distinct, very quirky appearance. They are flat fish with a diamond-shaped body, and start their lives swimming upright before they start swimming on their side after a couple of months. 

The olive flounder tend to enjoy swimming in coastal regions and like snacking on small fish and crustaceans. It’s also considered quite a delicacy for seafood enthusiasts, and can cost quite a lot when you are lucky enough to stumble upon it in a supermarket. 

7. Obese Synodontis (Synodontis obesus)

Despite its funny name, the obese synodontis isn’t actually obese. This spotted catfish does like to eat though, and it makes for a great scavenger for a home aquarium. With a keen sense of smell, this fish helps to keep your aquarium clean of crumbs and debris that could harm water quality. 

This particular kind of fish is also often referred to as an upside-down catfish because of its unique spine and barbels amongst other features. When an obese synodontis comes across potential predators in the water, it can actually emit an electric current into the water to scare them off. 

Freshwater Fish Starting With O

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Rhadinocentrus ornatus

1. One lined pencilfish (Nannostomus unifasciatus)

2. Olga cory (Corydoras simulatus)

3. Oneline tetra (Nannaethiops unitaeniatus)

4. Orange chromide (Etroplus maculatus)

5. Okefenokee pygmy sunfish (Elassoma okefenokee)

6. Ornate rainbowfish (Rhadinocentrus ornatus)

7. Ocellated puffer fish (Leiodon cutcutia)

8. One-gilled swamp eel (Ophisternon bengalense)

9. Orangespotted sunfish (Lepomis humilis)

10. Octozona barb (Eirmotus octozona)

11. Ornate pimelodus (Pimelodus ornatus)

12. Ocellated freshwater stingray (Potamotrygon motoro)

13. Otorongo ray (Potamotrygon castexi)

14. Orinoco peacock bass (Cichla orinocensis)

15. Onespot barb (Puntius terio)

16. Ornate tetra (Hyphessobrycon bentosi)

17. Oil catfish (Centromochlus perugiae)

18. Odynea pimelodid catfish (Pimelodella odynea)

19. Orinoco angelfish (Pterophyllum altum)

20. Okavango tilapia (Tilapia ruweti)

21. Oaxaca cichlid (Vieja zonata)

22. Odo cichlid (Nandopsis haitiensis)

23. Orangethroat darter (Etheostoma spectabile)

24. Ocellated snakehead (Channa pleurophthalma)

25. Ornate bichir (Polypterus ornatipinnis)

26. Ocellated bushfish (Ctenopoma muriei)

27. Oxyrhynchus tube-snouted ghost knifefish (Sternarchorhynchus oxyrhynchus)

28. Orange-finned danio (Danio kyathit)

29. Odessa barb (Puntius padamya)

30. Orange fin merry widow (Phallichthys amates)

31. One-lined African characin (Nannaethiops unitaeniatus)

32. Opaline gourami (Trichogaster trichopterus)

33. One spot betta (Betta unimaculata)

34. Obscure snakehead (Parachanna obscura)

35. Ocellate river stingray (Potamotrygon motoro)

36. Orange banded hillstream catfish (Akysis vespa)

Saltwater Fish Starting With O

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One-spot butterflyfish

1. One-spot butterflyfish (Chaetodon unimaculatus)

2. Okinawa goby (Gobiodon okinawae)

3. Ornate surgeonfish (Acanthurus dussumieri)

4. One-stripe anthias (Pseudanthias fasciatus)

5. Orange lined reef basslet (Liopropoma swalesi)

6. Orange diamond goby (Valenciennea puellaris)

7. Oxeye herring (Megalops cyprinoides)

8. Orange shoulder tang (Acanthurus olivaceus)

9. Orange blotch surgeonfish (Acanthurus olivaceus)

10. Orange skunk clownfish (Amphiprion akallopisos)

11. Orbicular batfish (Platax orbicularis)

12. One spot foxface (Siganus unimaculatus)

13. Orchid dottyback (Pseudochromis fridmani)

14. Oriole angel (Centropyge bicolor)

15. Ocellated lionfish (Dendrochirus biocellatus)

16. Ornate wrasse (Thalassoma pavo)

17. Orange-lined triggerfish (Balistapus undulatus)

18. Oblong blowfish (Takifugu oblongus)

19. Orange spotted sleeper goby (Valenciennea puellaris)

20. Orange lined cardinalfish (Apogon cyanosoma)

21. Orange anemonefish (Amphiprion sandaracinos)

22. Oualan forktail blenny (Meiacanthus oualanensis)

23. Ocellated dragonet (Synchiropus ocellatus)

24. Ocellaris clownfish (Amphiprion ocellaris)

25. Old glory (Amblygobius rainfordi)

26. Orange firefish (Nemateleotris magnifica)

27. Orange spotted shrimp goby (Amblygobius guttata)

28. Orange sea perch (Pseudanthias squamipinnis)

29. Orbiculate cardinalfish (Sphaermia orbicularis)

30. Orangebanded stingfish (Choridactylus multibarbus)

31. Oblique-lined dottyback (Cypho purpurascens)

32. Orange spotted goby (Amblyeleotris guttata)

33. Orangetip bristletooth (Ctenochaetus tominiensis)

Tropical Fish Starting With O 

1. Oranda (Carassius auratus auratus)

2. Otocinclus cat (Otocinclus vestitus)

3. Ornate wrasse (Thalassoma pavo)

4. Orangespine unicornfish (Naso lituratus)

5. Orange fin barb (Barbus eutaenia)

6. Onespot squeaker (Synodontis notata)

7. Orange clownfish (Amphiprion percula)

8. Orange spotted spinefoot (Siganus guttatus)

9. Ornate butterflyfish (Chaetodon ornatissimus)


This list of 75+ popular fish that start with O showcases just how much there is to know about the wonderful world of fish, from the tiny fish we keep at home in our aquariums to the massive and mysterious fish that lurk in the deepest realms of our oceans.

This list alone shows just how much there is for everyone to discover about the world of aquatic life. 

While there’s so much that continues to be discovered in our deep seas each day, there is still a vast area of all the earth’s water that no one has ever laid eyes on before. Perhaps one day we can make this list of fish with O names much longer than it is today. 

Ian Sterling

I've been keeping fish for over 30 years and currently have 4 different aquariums – it's an addiction. I'm here to teach you everything there is to know about fishkeeping.

I also use this site as an excuse to spend lots of money on testing and reviewing different aquarium products! You can find my reviews here.

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