Fish come in all shapes, sizes, and surprising forms—and some of them don’t look “fish-like” at all. Whether you’re exploring ocean habitats or animal adaptations, these wonderfully weird species deviate from the typical body form and appearance of other fish. Here are seven animals you might not realize are actually fish!
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Eels
With their long, ribbon-like bodies and reduced fins, eels can look more like snakes than fish. But eels are actually bony fish, members of the group Osteichthyes. That means an eel is more closely related to salmon, tuna, or even your pet goldfish than to any reptile!
Eels swim using wavelike movements along their bodies and use small pectoral fins to help them steer. Some species, like the electric eel, can even generate electric currents to stun prey—an adaptation very different from what we see in most fish.
Seahorses and sea dragons
Most fish swim horizontally, powered by the caudal (tail) fin. Seahorses and sea dragons break that rule completely. These unusual fish swim upright, using a small dorsal fin along their back for propulsion. Their long, flexible tails act like anchors, gripping seagrass or seaweed so they don’t drift away in the current.
These animals are wonderful examples of how the “basic fish body plan” can be reshaped for a very different lifestyle.
Mudskippers
When we picture fish, we imagine animals that must stay in the water to survive. Mudskippers challenge that idea! These remarkable fish live in tidal areas and regularly climb out onto mudflats.
Mudskippers can breathe air through their moist skin—similar to how amphibians like frogs breathe. And when they’re on land, they “walk” using their powerful pectoral fins. In most fish, these fins are only strong enough for steering in water, but mudskippers can support their weight on land. This unique ability gives scientists clues about how ancient fish may have taken the first steps toward life on land millions of years ago.
Sharks
Many students are surprised to learn that sharks are fish! Modern fish fall into three main groups: jawless fish, cartilaginous fish, and bony fish. Sharks belong to the cartilaginous fish group, meaning their skeletons are made of flexible cartilage instead of bone. Rays and skates are part of this group, too.
Sharks come in an incredible range of shapes and sizes—from 40-foot whale sharks to tiny lanternsharks. Some have unusual adaptations, like the hammerhead’s wide head that gives it nearly 360° vision, or the goblin shark’s extendable jaw. Diets vary widely as well: great whites hunt large prey, while whale sharks filter plankton from the water. Sharks live throughout the ocean, from deep-sea habitats to shallow coastlines.
Skates & Rays
Skates and rays look nothing like the “typical fish” silhouette. Their flattened bodies are perfectly suited for life along the seafloor, where they glide by flapping their broad, wing-like pectoral fins.
Although they look similar, skates and rays are not the same. Stingrays have a venomous barb on their tail—skates do not. In addition, skates tend to have thicker tails with small fins along them. Both are cartilaginous fish and excellent examples of body shapes adapted to a specialized habitat.
Lampreys
Fish were among the earliest vertebrates to evolve, and some ancient fish lived long before jaws existed. Today, the descendants of those early jawless vertebrates survive as lampreys and hagfish.
Lampreys lack jaws entirely. Instead of biting, they use a round, suction-like mouth with rasping teeth. Some species, like the sea lamprey, are parasites that attach to other fish and feed on their blood and body fluids. Their unusual anatomy makes them an important group for studying early vertebrate evolution.
Hagfish
Like lampreys, hagfish belong to the jawless fish group. They’re among the least “fish-like” fish, with long, slender bodies, soft pinkish skin, and no true eyes. At first glance, you might mistake a hagfish for a worm—until you learn that they have gills and other features that firmly place them within the fish lineage.
Hagfish are famous for one wild adaptation: they produce enormous amounts of sticky slime when threatened. This slime can clog the gills of predators, giving hagfish a unique way to escape danger.
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References and Further Reading
- Alaska Department of Fish and Wildlife (n.d.). Hagfish (Eptatretus deani) Species Profile. Available: https://www.adfg.alaska.gov/index.cfm?adfg=hagfish.main
- Clark, M., Douglas, M., Choi, J. (2018). Biology 2e. Open Stax. Ch. 29. Available: https://openstax.org/books/biology-2e/pages/29-2-fishes
- The Florida Aquarium (n.d.). Animal Spotlight: Mudskipper. Available: https://www.flaquarium.org/explore/habitats/morphd/mudskipper/
- MarineBio (n.d.). Great White Sharks, Carcharodon carcharias. Available: https://www.marinebio.org/species/great-white-sharks/carcharodon-carcharias/
- McGrouther, M. (2022). Goblin Shark. Australian Museum. Available: https://australian.museum/learn/animals/fishes/goblin-shark-mitsukurina-owstoni/
- National Geographic (n.d.). Hammerhead Sharks. Available: https://www.nationalgeographic.com/animals/fish/facts/hammerhead-sharks
- Reeves, N., et al. (2013). Concepts in Biology. Open Stax. Ch. 15.6. Available: https://openstax.org/books/concepts-biology/pages/15-6-vertebrates
- San Diego Zoo Wildlife Alliance (n.d.). Leopard Shark. Available: https://animals.sandiegozoo.org/animals/leopard-shark
- Spencer, P. (2019). What’s the Difference Between Stingrays and Skates? Ocean Conservancy. Available: https://oceanconservancy.org/blog/2019/12/12/whats-difference-stingrays-skates/
- U.S. Fish and Wildlife Service (n.d.). Sea Lamprey. Available: https://www.fws.gov/species/sea-lamprey-petromyzon-marinus