Unusual sea creatures encompass the ocean sunfish, a mysterious giant of the deep sea; the coelacanth, a living relic once deemed extinct; the humphead wrasse, a reef dweller that undergoes a gender transformation from female to male; the peculiar red-lipped batfish, discovered around the Galápagos Islands; and freshwater species like the candiru and alligator gar.
In this article, we delve into these and numerous other peculiar fish inhabiting the oceans, rivers, and lakes of the world.
Have you had the opportunity to observe any of these species? Which one is your favorite? Are there any extraordinary fish that we have overlooked? Let us know in the comments below!
Use the provided index to directly access a specific species or continue scrolling to explore all these bizarre creatures.
1. Alligator Gar
- Scientific name: Atractosteus spatula
- Family: Lepisosteidae
- IUCN conservation status: Least Concern
The Alligator Gar is a colossal freshwater fish endemic to North America. This unconventional-looking creature ranks among the largest freshwater fish on the continent, with some individuals exceeding 300 pounds in weight and stretching over 8 feet in length. Its name originates from the broad, alligator-like snout adorned with razor-sharp teeth.
As a top predator in its ecosystem, the Alligator Gar feeds on fish, turtles, and even small mammals. Despite its fearsome reputation, it poses no threat to humans and is a popular target for recreational fishing. With a lengthy lifespan, this species can survive for several decades in the wild.
2. Atlantic Wolffish
- Scientific name: Anarhichas lupus
- Family: Anarhichadidae
- IUCN conservation status: Vulnerable
The Atlantic Wolffish is a cold-water fish found in the North Atlantic Ocean, spanning from Greenland to Massachusetts.
This fish displays a distinct appearance, characterized by a large head and powerful jaws brimming with sharp teeth. Its elongated body is covered in dark, mottled scales, creating a somewhat snake-like visage.
Despite its menacing look, the Atlantic Wolffish, which can reach lengths of 1.5 meters, does not pose a significant threat to humans. It primarily feeds on crustaceans, mollusks, and other fish.
Due to overfishing and habitat destruction, the Atlantic Wolffish is classified as a vulnerable species. Consequently, protective measures are now in place in various regions.
3. Barreleye Fish
- Family: Opisthoproctidae
- Example species: Macropinna microstoma
Barreleyes, also known as spookfish, are diminutive deep-sea inhabitants. The Opisthoproctidae family encompasses 21 recognized species. Barreleyes possess an extraordinary transparent head, enabling them to see upward through their skull, detecting prey situated above them. Additionally, they possess large, telescopic eyes capable of rotating within the transparent dome of their head, enabling them to track both prey and predators.
4. Blobfish
- Scientific name: Psychrolutes marcidus
- Family: Psychrolutidae
- IUCN conservation status: Unassessed
The Blobfish, or smooth-head blobfish, resides in the depths of the ocean off the coasts of Australia, Tasmania, and New Zealand. Its unique gelatinous appearance has bestowed upon it the rather unflattering moniker.
The Blobfish’s body is adapted to survive in extreme depths, possessing very low density, allowing it to float just above the seafloor.
In its natural habitat, the blobfish appears almost normal. However, when brought to the surface where there is substantially less pressure, it begins to assume its “blobby” form.
5. Blue Parrotfish
- Scientific name: Scarus coeruleus
- Family: Scaridae
- IUCN conservation status: Least Concern
The Blue Parrotfish is a vibrant species inhabiting the coral reefs of the Western Atlantic Ocean, ranging from Florida to Brazil. Its name stems from its parrot-like beak, which it utilizes to scrape algae off coral reefs.
As a crucial player in maintaining the health of coral reef ecosystems, the Blue Parrotfish helps prevent the overgrowth of algae that can harm corals.
This species can grow up to 1.2 meters in length and weigh up to 20 kilograms. It is a sought-after target for recreational fishermen and is also commercially harvested for food. Nonetheless, the IUCN categorizes the Blue Parrotfish as Least Concern, as it has a relatively widespread distribution and is not significantly threatened by overfishing.
6. Candiru
- Scientific name: Vandellia cirrhosa
- IUCN conservation status: Not Evaluated
The Candiru, also known as the vampire fish or toothpick fish, is a parasitic freshwater catfish native to the Amazon Basin in South America.
This peculiar fish has gained notoriety for its alleged ability to enter human orifices, causing severe pain and potentially life-threatening complications.
Confirmed cases of candiru entering human bodies are exceedingly rare, with most reported incidents based on hearsay or anecdotal evidence.
Typically, the Candiru feeds on the blood of larger fish. Its small size and slippery skin enable it to enter the gill slits or other orifices of its larger hosts. It possesses a slender and elongated body, with jaws equipped with sharp teeth to latch onto its host.
Measuring less than 10 cm in length, the Candiru sports a gray-brown coloration, characterized by a flattened head and body.
7. Coelacanth
- Scientific name: Latimeria chalumnae
- Family: Latimeriidae
- IUCN conservation status: Critically Endangered
The Coelacanth is a rare fish believed to have gone extinct until its rediscovery in 1938 off the coast of South Africa.
Referred to as a “living fossil,” the Coelacanth has undergone minimal changes over the past 400 million years, making it a vital link in the evolution from fish to terrestrial vertebrates, including humans. Somewhere in your ancestral lineage lies a fish resembling the Coelacanth!
The West Indian Coelacanth is one of two living species, with the other being the Indonesian coelacanth (Latimeria menadoensis).
Reaching lengths of up to 2 meters and weighing up to 90 kilograms, the Coelacanth inhabits the deep waters around the Comoro Islands off the coast of East Africa. It is a slow-growing, long-lived species. Due to overfishing, bycatch in deep-sea trawling, and habitat destruction, the Coelacanth is critically endangered according to the IUCN.
8. Fangtooth
- Scientific name: Anoplogaster cornuta
- Family: Anoplogastridae
- IUCN conservation status: Least Concern
The Common Fangtooth is a deep-sea fish found in the world’s oceans, typically residing at depths of over 500 meters. Although small in size, growing up to 18 cm in length, it is renowned for its intimidating appearance.
With a large head adorned by oversized, sharp teeth, the Fangtooth boasts a menacing visage. Nevertheless, this peculiar fish does not pose a threat to humans, as it dwells in deep waters and is relatively small.
Commercial fishing of the Fangtooth is not prevalent, and its population is considered stable. Therefore, the IUCN classifies it as Least Concern.
9. Flying Fish
- Scientific name: Exocoetidae
- Family: Exocoetidae
- IUCN conservation status: Not evaluated
Flying fish comprise a group of approximately 50 species found in tropical and subtropical waters worldwide. They earned their name due to their remarkable ability to leap out of the water and glide through the air, using their wing-like fins to escape predators.
With streamlined bodies and impressive fins, flying fish can cover distances of up to 400 meters during their aerial adventures.
These fish play a crucial role in the food chain, serving as a vital food source for larger predatory fish and birds. Although not directly targeted by commercial fisheries, they occasionally become unintentional bycatch.
10. Frilled Shark
- Scientific name: Chlamydoselachus anguineus
- Family: Chlamydoselachidae
- IUCN conservation status: Near Threatened
The Frilled Shark is a peculiar deep-sea shark found in both the Atlantic and Pacific Oceans, typically inhabiting depths of up to 1500 meters. Its distinctive appearance includes a long, eel-like body and “frilly” or ruffled gill slits.
Reaching lengths of up to 2 meters, the Frilled Shark is a sluggish predator that feeds on various fish and squid. It rarely encounters humans and is not targeted in commercial fishing. However, it occasionally becomes unintentionally caught as bycatch.
The species is categorized as Near Threatened by the IUCN due to its low reproductive rate and vulnerability to overfishing.
11. Frogfish
- Family: Antennariidae
Frogfish are a family of small anglerfish that reside on the ocean floor in tropical and subtropical waters across the globe. Their name is derived from their resemblance to frogs, with their broad, flattened bodies and the ability to “walk” using their fins.
As ambush predators, frogfish feed on small fish and crustaceans. They possess the remarkable ability to change color and texture to blend seamlessly with their surroundings, making them difficult to detect by both prey and predators.
Their unique appearance and behavior make frogfish popular among divers and underwater photographers.
12. Giant Oarfish
- Scientific name: Regalecus glesne
- Family: Regalecidae
- IUCN conservation status: Least Concern
The Giant Oarfish is a deep-sea fish found in temperate and tropical waters worldwide. It holds the distinction of being the longest bony fish, with some specimens measuring up to 11 meters in length.
Sporting a long, slender body adorned with iridescent, silvery scales and a distinctive crest-like structure on its head, the Giant Oarfish is a mesmerizing sight.
Despite its enormous size, this species is solitary and feeds on plankton and small fish. It is not targeted in commercial fishing, and its population is considered stable.
13. Goblin Shark
- Scientific name: Mitsukurina owstoni
- Family: Mitsukurinidae
- IUCN conservation status: Near Threatened
The Goblin Shark is a deep-sea shark found in oceans worldwide, typically dwelling at depths of up to 1300 meters. Its most striking feature is its elongated, flattened snout covered in electroreceptor organs, which allow it to detect the electric fields emitted by its prey.
Measuring up to 4 meters in length, the Goblin Shark is a sluggish predator that feeds on a variety of fish and squid. It is seldom encountered by humans and is not specifically targeted by fishing operations. However, it occasionally becomes unintentionally caught as bycatch. The Goblin Shark is classified as Near Threatened by the IUCN due to its slow reproductive rate and susceptibility to overfishing.
14. Humphead Wrasse
- Scientific name: Cheilinus undulatus
- Family: Labridae
- IUCN conservation status: Endangered
The Humphead Wrasse, also known as the Napoleon Wrasse, is a large and colorful fish found in the tropical waters of the Indo-Pacific region.
This species stands out with its hump on the forehead, which gives it its name, and its impressive size. It can grow up to 6 feet in length and weigh over 400 pounds. The Humphead Wrasse is a solitary and slow-growing fish, with a lifespan of up to 30 years in the wild.
Unfortunately, the Humphead Wrasse is listed as Endangered by the IUCN due to overfishing for the live reef fish trade and habitat destruction. Conservation efforts are underway to protect this magnificent species and ensure its survival.
15. Jawfish
- Family: Opistognathidae
Jawfish belong to a family of small fish that inhabit the bottom of tropical and subtropical waters. They are known for their prominent jaws, which they use to dig burrows in the sand or rubble on the ocean floor.
What makes jawfish truly unique is their reproductive behavior. They are mouthbrooders, meaning the female jawfish lays the eggs, and the male jawfish keeps them safe in his mouth until they hatch.
With a length of less than 30 cm, jawfish feed on small crustaceans and other invertebrates. They are highly sought after by aquarium enthusiasts due to their colorful appearance and intriguing behavior.
16. Leafy Seadragon
- Scientific name: Phycodurus eques
- Family: Syngnathidae
- IUCN conservation status: Near Threatened
The Leafy Seadragon is an enchanting marine fish found exclusively in the southern coastal waters of Australia. It belongs to the Syngnathidae family, which also includes seahorses and pipefish.
This peculiar fish gets its name from its appearance, resembling a mythical creature with leaf-like projections covering its body. Growing up to 45 cm in length, the Leafy Seadragon is often found in seaweed beds and rocky reefs in shallow coastal waters.
Feeding primarily on small crustaceans and plankton, this species faces numerous threats. Habitat loss, pollution, and collection for the aquarium trade have led to its declining population. The Leafy Seadragon is currently classified as Near Threatened by the IUCN.
17. Lionfish
- Scientific name: Pterois volitans
- Family: Scorpaenidae
- IUCN conservation status: Least Concern
Lionfish are venomous marine fish native to the tropical Indo-Pacific region. Their striking appearance, with brightly colored fins and a spiky exterior, has made them popular in the aquarium trade.
While visually captivating, lionfish have become invasive species in many parts of the world. Their introduction to non-native habitats has caused significant ecological damage. They have no natural predators and reproduce rapidly, posing a threat to native fish populations.
The red lionfish, Pterois volitans, is a well-known species that can grow up to 38 cm in length. It feeds on a variety of fish, crustaceans, and small marine organisms. Efforts are underway to manage lionfish populations and minimize their impact on vulnerable ecosystems.
18. Longhorn Cowfish
- Scientific name: Lactoria cornuta
- Family: Ostraciidae
- IUCN conservation status: Unassessed
The Longhorn Cowfish is an intriguing marine species found in tropical waters of the Indo-Pacific region. It belongs to the family Ostraciidae, which also includes boxfish and trunkfish.
The Longhorn Cowfish derives its name from the long, pointed horns on its head, which it uses for defense and foraging. These projections also make it more challenging for predators to swallow. Interestingly, when stressed, this unique fish is capable of secreting poison from its skin.
Measuring up to 50 cm in length, the Longhorn Cowfish typically inhabits shallow coral reefs and seagrass beds. Its diet consists of small invertebrates, crustaceans, and algae. While it can be found in the aquarium trade, it can be challenging to maintain in captivity.
19. Megamouth Shark
- Scientific name: Megachasma pelagios
- Family: Megachasmidae
- IUCN conservation status: Data Deficient
The Megamouth Shark is a rare and enigmatic deep-sea shark first discovered in 1976. It belongs to the family Megachasmidae, which also includes the Whale Shark and Basking Shark.
This extraordinary shark derives its name from its massive mouth, which it uses to filter-feed on plankton and small fish. It can grow up to 5.5 meters in length and is typically found in deep waters ranging from 120 to 1,200 meters. Due to its elusive nature and deep-sea habitat, little is known about its biology and behavior.
The Megamouth Shark is classified as Data Deficient by the IUCN due to insufficient information to assess its conservation status accurately. Further research and study are needed to gain a comprehensive understanding of this remarkable species.
20. Mekong Giant Catfish
- Scientific name: Pangasianodon gigas
- Family: Pangasiidae
- IUCN conservation status: Critically Endangered
The Mekong Giant Catfish is a large freshwater fish native to the Mekong River in Southeast Asia. It holds the title of the world’s largest freshwater fish, capable of reaching lengths of up to 3 meters and weighing up to 300 kilograms.
Unfortunately, the Mekong Giant Catfish is facing severe threats. Overfishing, habitat loss, and the construction of dams and other water development projects have caused a drastic decline in its population. It is estimated that only a few hundred individuals remain in the wild.
Considered a delicacy in some parts of Asia, the Mekong Giant Catfish is highly sought after in the commercial fish trade. Efforts are being made to protect and conserve this species, but its future remains uncertain. Conservation measures and sustainable fishing practices are vital for the survival of this magnificent giant.
21. Moonfish
- Scientific name: Lampris guttatus
- Family: Lampridae
- IUCN conservation status: Least Concern
The Moonfish, also known as Opah, is a large and vibrant deep-sea fish found in temperate and tropical oceans worldwide.
With a circular body shape and iridescent, silvery scales, the Moonfish is a striking sight. It is one of the few “warm-blooded” fish, capable of maintaining a body temperature higher than the surrounding water. This unique adaptation allows it to thrive in the cold depths of the ocean.
The Moonfish feeds primarily on squid and small fish, playing a crucial role in the marine ecosystem. While it is not a targeted species in commercial fisheries, it may occasionally become bycatch.
Due to its wide distribution and relatively stable population, the Moonfish is classified as Least Concern by the IUCN. However, continued monitoring and conservation efforts are necessary to ensure its long-term survival.
22. Ocean Sunfish
- Scientific name: Mola mola
- Family: Molidae
- IUCN conservation status: Vulnerable
The Ocean Sunfish, also known as the Mola Mola, is a truly remarkable and distinct fish found in tropical and temperate oceans around the world. It holds the title of being one of the largest bony fish on Earth, with some individuals reaching lengths of up to 3 meters and weighing over 2,000 kilograms.
The Ocean Sunfish possesses a unique body shape that is almost circular, with a flattened appearance. It lacks a true tail fin and has a unique swimming style, lazily drifting through the water using its large dorsal and anal fins.
While its immense size is awe-inspiring, the Ocean Sunfish primarily feeds on small fish, crustaceans, and jellyfish. Its diet, along with its preferred warm-water habitats, makes it susceptible to plastic pollution, as it may mistake floating debris for jellyfish.
Due to overfishing, habitat degradation, and bycatch in fishing gear, the Ocean Sunfish is listed as Vulnerable by the IUCN. Conservation efforts are crucial to protect this fascinating and vulnerable species.
23. Ocellated Icefish
- Scientific name: Chaenocephalus aceratus
- Family: Channichthyidae
- IUCN conservation status: Not Evaluated
The Ocellated Icefish, also known as the Pearly Icefish, is an intriguing fish species inhabiting the icy waters of the Southern Ocean surrounding Antarctica. It belongs to the family Channichthyidae, which is collectively known as icefishes for their adaptation to survive in extreme cold conditions.
What sets the Ocellated Icefish apart from other fish species is the lack of hemoglobin in its blood, giving it a translucent appearance. This unique adaptation allows the Ocellated Icefish to obtain sufficient oxygen directly from the cold Antarctic waters without the need for red blood cells.
Feeding primarily on krill and other small crustaceans, this fish plays a vital role in the Antarctic food chain. While its conservation status has not been evaluated by the IUCN, the delicate ecosystem of the Southern Ocean underscores the need for further research and conservation efforts to protect this extraordinary species.
24. Psychedelic Frogfish
- Scientific name: Histiophryne psychedelica
- Family: Antennariidae
- IUCN conservation status: Not Evaluated
Among the many strange fish species, the Psychedelic Frogfish stands out for its vibrant and eye-catching appearance. This species is found in the waters around Ambon Island and other Indonesian islands. It belongs to the family Antennariidae, known for their anglerfish-like predatory behavior.
The Psychedelic Frogfish earns its name from its brightly colored patterns of red, yellow, and white, making it a mesmerizing sight. With its flattened body and a lure on its head, it attracts prey towards its formidable jaws.
Measuring only about 9 centimeters in length, this small fish remains a mystery in terms of its ecology and behavior. Further research is needed to uncover the secrets of this extraordinary species and its role in the marine ecosystem.
25. Red-Bellied Piranha
- Scientific name: Pygocentrus nattereri
- Family: Serrasalmidae
- IUCN conservation status: Unassessed
The Red-Bellied Piranha is a freshwater fish native to the rivers and lakes of South America. This species is widely recognized for its fearsome reputation and razor-sharp teeth.
With a squat and powerful body, the Red-Bellied Piranha grows to a length of approximately 50 cm. Contrary to popular belief, piranhas are not indiscriminate man-eaters. They primarily feed on a diet of plants, small to medium-sized animals, and scavenged carrion. While they possess a set of sharp teeth, their feeding behavior is often exaggerated in popular culture.
Red-Bellied Piranhas are highly social and live in schools, exhibiting cooperative hunting behavior. They play an important role in regulating the populations of smaller aquatic animals within their ecosystems.
Although not assessed by the IUCN for conservation status, the Red-Bellied Piranha faces localized threats due to overfishing, habitat destruction, and water pollution. Sustainable management practices and conservation efforts are crucial for maintaining the balance of freshwater ecosystems and ensuring the survival of this iconic species.
26. Red-Lipped Batfish
- Scientific name: Ogcocephalus darwini
- Family: Ogcocephalidae
- IUCN conservation status: Least Concern
The Red-Lipped Batfish is an extraordinary fish found in the deep waters surrounding the Galapagos Islands and off the coast of Peru. Belonging to the family Ogcocephalidae, this fish possesses distinctive bright red lips, contrasting against its mottled brown body.
With its flattened body and modified pectoral fins, the Red-Lipped Batfish uses a unique “walking” motion along the seafloor to navigate its surroundings. While its appearance may seem comical, it serves a purpose in attracting prey.
This species primarily feeds on small invertebrates and crustaceans, using its specialized hunting techniques to secure its meals. Despite its limited range, the Red-Lipped Batfish is classified as Least Concern by the IUCN, indicating a relatively stable population.
Preserving the marine habitats surrounding the Galapagos Islands and implementing sustainable fishing practices are crucial for the long-term conservation of this fascinating and peculiar species.
27. Sawfish
- Scientific name: Pristidae (family)
- IUCN conservation status: See text
Sawfish, belonging to the family Pristidae, are a group of ray-like fish known for their unique long, flat snouts lined with sharp teeth. They inhabit coastal waters of the Atlantic and Indo-Pacific regions. Five distinct species of sawfish are currently recognized, all of which are endangered, with four out of the five considered critically endangered.
These remarkable fish are threatened by overfishing, habitat loss, and incidental capture in fishing gear. Sawfish are highly valued for their distinctive snouts and other body parts, making them targets for illegal trade.
Efforts are being made to protect and conserve sawfish populations worldwide. Conservation measures include fishing regulations, habitat restoration, and public awareness campaigns to highlight the importance of these fascinating and imperiled creatures.
28. Stargazer
- Scientific name: Uranoscopidae (family)
Stargazers, belonging to the family Uranoscopidae, are a diverse group of fish characterized by their unique and unusual appearance. With their upward-facing eyes and flattened, bony heads, they appear to be gazing at the stars. These adaptations enable them to bury themselves in the sand and ambush their unsuspecting prey.
Stargazers possess venomous spines on their back and gill covers, providing them with a means of defense against potential threats. Some species even have the ability to produce electricity, using it to shock their prey.
Found in both saltwater and freshwater habitats, including coral reefs and sandy bottoms, stargazers exhibit variations in size and coloration across different species.
An example of a stargazer species is the whitemargin stargazer, Uranoscopus onnah, which inhabits the tropical and subtropical waters of the Indo-Pacific region, ranging from the Red Sea to the western Pacific Ocean.
29. Yellow Boxfish
- Scientific name: Ostracion cubicus
- IUCN conservation status: Least Concern
The Yellow Boxfish, also known as the Cube Boxfish or Yellow Trunkfish, is a captivating marine fish belonging to the family Ostraciidae. It can be found in the shallow tropical and subtropical waters of the Atlantic Ocean, ranging from the eastern coast of the United States to South America and throughout the Caribbean Sea.
Characterized by its box-shaped body covered in bony plates, the Yellow Boxfish showcases a vibrant yellow coloration with a distinct black spot on its dorsal fin. It can grow up to 45 cm in length, making it a relatively small member of its family.
Feeding mainly on algae and small invertebrates, the Yellow Boxfish plays a crucial role in maintaining the health of coral reef ecosystems. It is also known for its ability to release toxic substances when stressed, providing a form of defense against potential predators.
Currently assessed as Least Concern by the IUCN, the Yellow Boxfish benefits from its relatively stable population. However, ongoing efforts to conserve and protect coral reefs and reduce the impacts of pollution and habitat destruction remain essential for the long-term survival of this fascinating species.
These extraordinary fish species, each with their own unique characteristics and adaptations, highlight the incredible diversity and wonders of the underwater world. Understanding and appreciating these weird and wonderful creatures can inspire conservation efforts and promote the sustainable management of our oceans, ensuring their preservation for generations to come.