Did you know there are nearly 250,000 recorded marine species? It’s no wonder scuba divers have a hard time identifying what they’ve spotted. What’s more, there are countless animals that look alike!

Here are some commonly seen (and confused) underwater animals that look alike — and how you can tell these ocean doppelgängers apart from one another.

Sailfish and Marlins

Part of the billfish family, sailfish and marlins have spear-like rostrums and are fast, ferocious hunters. While both have sail-like dorsal fins, the marlin’s is smaller and slopes into a triangular ‘peak’.

A side-by-side photo comparison of a sailfish and a marlin, two billfishes which are underwater animals that look alike
L-R: Sailfish and striped marlin

Leafy and Weedy Seadragons

Leafy seadragons are adorned with appendages that mimic their kelpy South Australian habitat. On the other hand, the sleeker weedy seadragons swap decorations for a camouflage of yellows, reds, and vibrant purples.

A side-by-side photo comparison of a leafy seadragon and weedy seadragon, two South Australian sea creatures that look alike
L-R: Leafy seadragon and weedy seadragon

Hawksbill and Green Sea Turtles

While other turtles (such as leatherbacks) are more distinctive, many divers get muddled between these two. Nevertheless, the best way to identify them is by their beak; hawksbills’ beaks are sharper and hook-like, whereas green turtles’ beaks are more rounded.

A side-by-side photo comparison of hawksbill and green turtles, two beautiful sea creatures that are often confused by divers
L-R: Hawksbill turtle and green turtle

Stonefish and Scorpionfish

Both are indeed masters of camouflage, but look closely. Stonefish have rounder bodies and grumpier mouths, while scorpionfish’s eyes stick out more. They both possess venomous spines, but the stonefish’s are thicker and more lethal.

A side-by-side photo comparison of a scorpionfish and a stonefish, two venomous and weird sea creatures that look alike
L-R: Scorpionfish and stonefish

Longfin Bannerfish, Schooling Bannerfish, and Moorish Idols

These almost-identical bannerfish species are members of the butterflyfish family and are often seen in large groups. They also bear an uncanny resemblance to Moorish idols (solitary relatives of surgeonfish). To spot the difference, just compare both tails and snouts!

A side-by-side photo comparison of silver, yellow and black bannerfish and Moorish idols, two species of fish that look alike
L: Moorish idols (Credit: Brocken Inaglory), R: Schooling bannerfish

Trumpetfish and Cornetfish

It’s easy to mix up these two elongated fish that look alike, but watch them move: trumpetfish are stiff swimmers, while cornetfish bend and flex more. Cornetfish’s tails are also flourished with a signature ‘filament’.

A side-by-side photo comparison of a trumpetfish and a cornetfish, two elongated and curious marine animals that look alike
L: Trumpetfish (Credit: Nick Hobgood / expanded from original), R: Cornetfish (Credit: John Turnbull, cropped from original)

Seals and Sea Lions

Unlike seals, sea lions have external ear flaps and are usually noisier. However, the clearest contrast between these pinnipeds is in movement: sea lions ‘walk’ on their flippers, while seals ‘galumph’ on their bellies.

A side-by-side photo comparison of a sea lion and a seal, playful animals that look alike but can be identified in movement
L-R: California sea lion and Hawaiian monk seal

Prawns and Shrimp

Often referred to interchangeably, these are actually unique underwater animals. You’ll typically find shrimp in colder saltwater, while prawns prefer warmer freshwater — though there are exceptions. Prawns have more claws but can’t curl up their bodies in the same way as shrimp.

A side-by-side photo comparison of a tiger shrimp and common prawn, two different sea creatures that are often misidentified
L: Giant tiger prawn (Credit: Marine Research / cropped from original), R: Common prawn

Humphead (Napoleon) Wrasse and Bumphead Parrotfish

With bulging foreheads, these giant fish match in appearance and name! Fortunately, telling the difference between them is easy. Bumphead parrotfish have hard, beak-like mouths, while Napoleon wrasse have large, fleshy lips.

A side-by-side photo comparison of bumphead parrotfish and a Napoleonfish, which have big heads and are fish that look alike
L-R: Bumphead parrotfish and humphead (Napoleon) wrasse

Pufferfish and Porcupinefish

Pufferfish and porcupinefish (aka blowfish) can both inflate themselves and produce deadly tetrodotoxin to defend against predators. However, pufferfish have smooth skin, while porcupinefish use bony spines as extra armor.

A side-by-side photo comparison of a pufferfish and a porcupinefish, two animals that look alike and are toxic to predators
L: Dog-faced pufferfish, R: Long-spined porcupinefish (Credit: Malene Thyssen / cropped from original)

Dolphins and Porpoises

There are many differences between these cetaceans. From the surface, the quickest clue is the dorsal fin; dolphins’ dorsal fins are curved, while porpoises’ dorsal fins are more triangular. If you’re lucky enough to get a closer look, you’ll also notice that porpoises lack the long beak that dolphins have.

A side-by-side photo comparison of dolphins playing in the surf and the dorsal fin of a porpoise, two animals that look alike
L: Bottlenose dolphins, R: Harbor porpoise (Credit: Marine England / cropped from original)

Goldband Fusiliers and Yellowtail Snappers

While these two fishes look similar, goldband fusiliers mainly live around Florida, the Caribbean, and the Gulf of Mexico. On the other hand, yellowtail snappers are native to Indo-Pacific regions. In addition, check out their tails: fusiliers have two distinguishing black spots.

A side-by-side photo comparison of goldband fusiliers and a yellowtail snapper, two common reef fish that look alike
L: Goldband fusiliers (Credit: Randall, J.E. / expanded from original), R: Yellowtail snapper (Credit: Andy Blackledge / cropped from original)

Butterfish (Rock Gunnels) and Greater Pipefish

Residents of UK waters, both species are long, thin, and well-camouflaged among rocks and kelp. However, pipefish have trumpet-like snouts, while butterfish are eel-like with unmistakable black dots along their back.

A side-by-side photo comparison of a greater pipefish and a butterfish (rock gunnel), two elongated fish that look alike
L: Greater pipefish (Credit:
Roberto Pillon / cropped from original), R: Butterfish (Credit: Jack Sewell / cropped from original)

Manatees and Dugongs

Nicknamed ‘sea cows’, these are two frequently confused animals that look alike. However, the easiest way to tell sirenians apart is by their body shape. Dugongs have ‘whale-shaped’ tails and long, broad snouts, while manatees have ‘paddle’ tails and short, rounded snouts.

A side-by-side photo comparison of a dugong and a manatee, two animals that look alike but have different tails and mouths
L-R: Dugong and manatee

Mimic Octopuses and… Everything!

These intelligently deceptive critters can mimic other animals to aid hunting and defense. In fact, they can impersonate over 15 other species, including lionfish, sea snakes, flatfish, crustaceans, and jellyfish. This certainly makes fish identification trickier!

Two photos of a mimic octopus, a striking and well-camouflaged cephalopod that impersonates 15 other species of marine life

One Fish, Many Names

To complicate fish ID even more, some sea creatures that look alike are, in fact, the same animals with different names. These might come from regional variations, folklore, changes in taxonomy, or nicknames. For example:

An orca (also called a killer whale or blackfish) breaching, and an example of the same animals with different names

How to Identify Underwater Animals That Look Alike

There are plenty of ways to identify animals that look alike. In particular, the PADI Fish Identification course will teach you how to recognize and reference the different sea creatures you see on dives. You’ll learn about the characteristics of fish families and species, survey techniques, and tips for protecting marine life.

Two scuba divers watching and naming different colorful reef fish while taking a PADI Fish Identification specialty course

Knowing what creatures you’ve seen (and being able to tell others) will make your dives even more memorable and enjoyable. Start today with PADI eLearning!

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