Skip to main content

10 Rarest Fish in the World

Errah is a bookwormy and logophilic writer and science & technology teacher. He often writes about scientific ideas, theories, and research.

Read on to learn about the 10 rarest fish in the world, including the Tequila splitfin and the incredibly elusive ornate sleeper ray.

Read on to learn about the 10 rarest fish in the world, including the Tequila splitfin and the incredibly elusive ornate sleeper ray.

The top 10 rarest fishes in the world are covered in this article. They are considered rare species because they are either thought to be extinct in the wild, are severely endangered, or can be quite difficult to find in their natural habitat. Here are the 10 fish we'll look at:

Top 10 Rarest Fish on Earth

10. European Sea Sturgeon

9. Smalltooth Sawfish

8. Kissing Loach

7. Giant Sea Bass

6. Tequila Splitfin

5. Adriatic Sturgeon

4. Devil's Hole Pupfish

3. Red Handfish

2. Sakhalin Sturgeon

1. Ornate Sleeper Ray

10. European Sea Sturgeon

The European sea sturgeon (Acipenser sturio) is a critically endangered fish that was previously common throughout Europe but now only exists in a basin in France. Only 800 of this kind of bony fish remain on our planet. This number, in fact, was derived from a nearly extinct population of a single pair of European sea sturgeon that had been bred to enhance their numbers. Thanks to the French government's efforts to conserve and expand its population, this fish is still in existence.

The European sea sturgeon is a huge fish that may reach a length of 6 meters (20 feet) and weigh up to 400 kilograms (880 pounds). The fish has a wedge-shaped head with a pointy snout and a face covered in sensitive barbels. The body of this fish is olive-brown on top and the underbelly is white. It features five lines of large plates that are made of bones.

The European sea sturgeon is diadromous, meaning it can live in both freshwater and saltwater environments. It lives in the sea most of the time but migrates to rivers to breed. It is a carnivore and prefers crustaceans, worms, and mollusks as food. It uses its barbels to hunt for prey in the mud and sands underwater.

Smalltooth Sawfish

Smalltooth Sawfish

9. Smalltooth Sawfish

The smalltooth sawfish (Pristis pectinata) is a cartilaginous fish related to rays and skates. It belongs to the sawfish family (Pristidae). All members of this family have a shark-like appearance with flattened heads and trunks. However, their most distinctive feature is the rostrum, which is a very long, saw-like "nose" that is flanked on either side by a row of sharp teeth. The teeth that run down the rostrum's side edges are actually modified scales rather than true teeth. The rostrum is used for hunting and feeding. The sawfish uses this anatomical trait to slice its prey into pieces by swiftly slashing the rostrum side to side. It is also used as a line of defense against predators.

The smalltooth sawfish is distinguishable from other sawfishes by having small “teeth”, hence its name. It can grow an average of 18 feet (5.5 meters) in length. It is found off the coast of Florida. It is a critically endangered species, with only 250 to 500 individuals remaining on the planet according to International Union for Conservation of Nature.

8. Kissing Loach

The Kissing Loach (Parabotia curtus) is a critically endangered Japanese fish that lives only in a few river systems in Japan and migrates to flooded paddy fields to spawn. It is estimated that there are no more than 800 kissing loaches left in the land of the rising sun. It is thought to be extinct in the wild. According to the IUCN Red List, if conservation efforts are not continued, all remaining Kissing Loach populations will become extinct.

The kissing loach is a small freshwater fish that grows to be only 6 inches long. The elongated body is dark brown, with lighter brown stripes. The head is pointed, and there are six barbels near the mouth. These barbels have taste buds that help the fish find food in murky waters. They survive by scavenging and feeding on mud worms.

7. Giant Sea Bass

The giant sea bass (Stereolepis gigas) is a massive fish native to California, USA. It can grow to be more than 7 feet long and 700 pounds. When young, this fish is orange with black spots, but as it matures, it turns bluish-black with larger spots and a white underside. Its color can also shift from normal to light gray to warn other giant sea basses of predators.

Though it is named “bass”, it is a member of the wreckfish family. It prefers to live at depths ranging from 10 to 40 meters on sandy bottoms, kelp beds, rocky reefs, and ridges to ambush prey. It feeds on crustaceans, rays, skates, squid, fish, and occasionally kelp. The giant sea bass is a critically endangered species, with only about 500 individuals remaining in the ocean.

6. Tequila Splitfin

The Tequila splitfin (Zoogoneticus tequila) is a very small fish found only in a small pond near Mexico’s Tequila volcano. They were previously considered extinct in the wild due to pet ownership and were only thought to live in aquariums. However, in 2014, following a successful conservation effort, they were successfully restored to the wild. Today they can currently be found in the wild in numbers of 500 or less.

Regarding physical characteristics, the tequila splitfin shows sexual dimorphism, meaning males and females can be distinguished from one another due to systemic differences such as size. Males usually have a smaller body size than females. Males are just 3 cm, compared to females' 5 cm growth potential.

Both sexes have olive bodies but the males' are deeper in color. Additionally, the males have an orange C-shaped band adorning their caudal fin while that of females is completely translucent. Regarding the Tequila splitfin diet, they are a carnivorous species that eat primarily small aquatic invertebrates and insect larvae.

5. Adriatic Sturgeon

The Adriatic sturgeon (Acipenser naccarii) belongs to the same genus as the European sea sturgeon. It dwells in the Adriatic Sea, a body of water that is surrounded by Greece, Albania, Italy, and other nations. The Adriatic sturgeon is a huge fish that can grow as long as 2 meters. It shares similar characteristics with other sturgeons, including an elongated body, a skeleton that is partially cartilaginous, and the bony plates lining the body. It is also diadromous.

It can be distinguished from other sturgeons by the color pattern and shape of its body. Its favorite food includes aquatic bug larvae, small fishes, crustaceans and mollusks. It is critically endangered, and there may be no more than 250 wild fish surviving, according to the IUCN Red List.

Devils Hole Pupfish

Devils Hole Pupfish

4. Devil's Hole Pupfish

The Devil's Hole pupfish (Cyprinodon diabolis) are extremely rare that can only be found in a small puddle in a fissure of a rocky geological formation in Nevada's Amargosa Valley. At the time of the most recent count, only about 170 of these fish were present in their location, but prior to that, the smallest count of these species was 35. Researchers believe that the number of these fish only rose due to reproduction, but 170 is still a modest number. They are still quite rare and considered critically endangered fish.

The tiny Devil's Hole pupfish seldom surpass 0.8 in (2 cm). They can be distinguished from other pupfish by their lack of pelvic fins and, in adult males, by the absence of vertical crossbars. Males have an iridescent, dark blue body and a black band on their tail; females and juveniles, however, are yellow-brown and lack a band.

Algae are their main food source but they have occasionally been observed eating tiny invertebrates. The fish were given that name due to their playful nature, which resembles that of pups; and the Devil's Hole is the name of the crack or fissure that they inhabit.

3. Red Handfish

With less than 100 thought to still survive, the red handfish (Thymichthys politus) is regarded as critically endangered. Their range is constrained, and they are only known to live in two small, coral patches in southeast Tasmania, an Australian island state.

They are very small species with an average standard length of 6 cm (2.4 in) to 8 cm (3.2 in). They are unable of swimming like other handfishes and must instead "walk" about on their unique, hand-like pectoral fins. They come in two different color variations—one brown or white with red accents, and the other a solid red coloring. Red handfishes are benthic creatures and are frequently spotted foraging for worms and crustaceans on the stony and sandy substrate.

Sakhalin Sturgeon

Sakhalin Sturgeon

2. Sakhalin Sturgeon

The Sakhalin Sturgeon (Acipenser mikadoi) is another rare sturgeonfish on the list. This fish was abundant in Japanese markets around the 1950s, but its population declined due to overfishing. It is generally thought to be extinct in the wild. According to the IUCN, only 10 to 30 sakhalin remain in the world, and experts believe it will go extinct within the next 15 years, but captive breeding efforts are taking place.

The Sakhalin sturgeon can reach lengths of up to 8 feet and weights of up to 330 pounds. The species has an olive-green back and a white underbelly with a yellow-green undertone. Its main food sources are fish, worms, and crustaceans.

1. Ornate Sleeper Ray

The ornate sleeper ray ( Electrolux addisoni) is not actually highly endangered. The population is unknown, and there are few studies about this species due to the fact that it has only ever been seen four times in different locations off the coast of South Africa, making this ray rare. It was seen for the first time in 1984.

The ornate sleeper ray belongs to an order of electric rays well-known for being able to generate an electric discharge that can be utilized for defense as well as to stun prey. It feeds on polychaetes worms and small crustaceans to survive. The body of this species is shaped like a flat, circular "disk," while the tail resembles a shark's. It can be set apart from other electric rays by its color pattern, which is made up of a dark brown base with yellow specks and a tangle of black stripes.

Sources and Further Reading

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Errah Caunca