See-through fish are a subject of fascination for a myriad of reasons: Not only are they incredibly difficult to spot, there is a practical, evolutionary reason for why they exist – protection. Transparent fish have the ability to hide in plain sight.
While land animals have the luxury of hiding in trees or camouflaging in foliage, the vast, open ocean provides no hiding spots. This is why transparency, a quality where animals allow up to 90% of light to pass through their bodies, can be crucial for survival.
To shed some light (pun intended) on the world of see-through fish, we’ve compiled a list of 27 interesting clear animals that exist in the ocean.
1. Barreleye Fish
Barreleye Fish are also known as the Spook Fish, and it’s easy to see why. Featuring a fully transparent head and an opaque body, it’s easy to be caught off guard by the stark contrast between both parts of its body.
However, this serves a functional purpose. Their transparent heads allow this deep-sea fish to see through their foreheads and protect their sensitive eyeballs.
2. Cyanogaster noctivaga
Native to Brazil and only recently discovered in 2013, Cyanogaster noctivaga literally translates to “The Blue-Bellied Night Wanderer” due to its distinctive blue belly and nocturnal habits.
With the exception of its large eyes, reddish head, and blue belly, this fish has a fully transparent body, causing it to appear as a blue streak as it swims about in the night.
3. Crocodile Icefish
As its name would suggest, the Crocodile Icefish lives in frigid cold temperatures and has an icy appearance caused by its clear blood.
The lack of hemoglobin in its blood gives it this rare quality. Though hemoglobin is required in most animals to carry oxygen, the Crocodile Icefish does without because its cold surroundings allows for a greater degree of oxygen solubility in its blood.
4. Transparent Juvenile Surgeonfish
If the transparent juvenile surgeonfish reminds you of a cartoon character, that’s because it’s a close relative of the Dory fish. (Finding Nemo, anyone?)
The bluish tint surrounding its gills is particularly reminiscent of the beloved cartoon character, though its transparent body may catch Nemo enthusiasts off-guard. Nevertheless, it’s still every bit as cool as its cartoon counterpart!
5. Transparent Flatfish
The transparent flatfish is unique in that it is almost entirely colorless, making it virtually see-through. Like other flatfish, these sea creatures are bottom-dwelling, and have both eyes on one side of their body.
6. Ghost catfish
For those of you looking to house a transparent sea creature in your aquarium, the ghost catfish is for you.
These interesting fish hail from the rivers of Thailand, and are at home in a community tank filled with other peaceful fish.
7. Glass Eel
Fully see-through except for their outlines and a rudimentary gut, glass eels are actually leptocephalus – eels in their larval stage. As they mature, they gradually lose this transparent quality.
Besides being fully transparent, leptocephalus also possesses fang-like teeth. These traits protect them against predators – something that’s extremely useful as their larval stages can last up to a year.
8. Juvenile Cowfish
As an adult, the Roundbelly Cowfish appears as a solid-colored fish with brown and yellow splotches on its body. However, juveniles are marked by their transparent bodies and bioluminescent glow.
To evade detection by predators, juvenile cowfish have the ability to turn their bioluminescence off, making them appear almost invisible.
Transparent Squids and Octopus
9. Glass Squid
Like most clear animals, the glass squid’s transparent body serves a protective function by allowing it to camouflage into its environment.
Fully transparent except for their arms, guts, and eyes, the Glass Squid is incredibly difficult to spot. Some genuses are even capable of injecting ink into their bodies, allowing them to appear opaque for short periods of time!
10. Juvenile Sharpear Enope Squid
A favorite among nature photographers, the Juvenile Sharpear Enope Squid is truly one-of-a-kind.
Red polka dots feature prominently on an otherwise transparent body, while its bioluminescent internal organs add to its otherworldly appearance.
11. Glass Octopus
Commonly found in tropical and subtropical oceans, the glass octopus is notoriously difficult to spot. Though these masters of camouflage have sparse red spores on their skin, these spores appear black in the deeper parts of the ocean.
Couple that with the fact that their skin is entirely translucent, and you’ll understand just why this sea creature is so elusive.
12. Ghost Shrimp
If you’re searching for a helpful, bottom-feeding addition to your tank, the Ghost Shrimp is for you. These transparent sea creatures feast on algae and uneaten food that sink to the bottom of the tank.
These helpful critters have a fully transparent body and an exoskeleton. They moult several times over the course of their lives, which makes them entertaining critters to watch.
Never judge a book by its cover – the phronima’s minuscule size belies its parasitic killer instincts. These semi-transparent creatures rely on hollowed-out bodies of other transparent fish for protection.
Using their sharp claws, the Phronima slices open the body of its victims before creating a protective barrel out of carcasses, in which it travels and houses its young.
14. Cystisoma Neptuni
Featuring a large pair of bright orange eyes, the Cystisoma Neptuni is a species of amphipod that measures up to 7 inches long.
Being larger than most other amphipods, it has an almost entirely see-through body to hide it from the sight of predators. Even its gut is see-through, appearing only as a faint blue outline.
Transparent Snails and Slugs
15. Zospeum tholussum
Discovered in one of the deepest cave systems in the world, it comes as no surprise that the Zospeum tholussum is considered one of the very few animals on earth to be an exclusive cave-dweller.
These snails have fully translucent shells and no eyes, making them unique and interesting from a biological standpoint.
16. Phylliroe bucaphalum
The phylliroe bucaphalum is a genus of pelagic parasitic nudibranch – a type of sea slug that feeds on jellyfish and plankton.
Its guts are visible through its flattened, transparent body, and its long, nose-like structures lends it a distinctive silhouette.
17. Sea Angel
Almost everyone does a double take when they first lay eyes on the Sea Angel. Resembling a snow angel, these ethereal-looking transparent creatures are actually a type of sea slug.
18. Glass Frog
From the top, the Glass Frog looks like any other frog due to its vivid green back skin. However, it catches one by surprise as it has see-through skin on its abdomen, chest, and legs.
This feature allows the Glass Frog to blend in with its surroundings, as the translucent skin reduces the color contrast between the frog’s vivid green outlines and the color of the leaves it rests on.
Transparent Jellies (Comb Jellies, Salps, Jellyfish)
19. Common Jellyfish (Moon Jellies)
In spite of what its name may suggest, jellyfish have more in common with corals and sea anemones than actual fish. They all possess cnidocytes – a venom-filled stinging cell used to capture prey, giving jellyfish its poisonous reputation.
Lacking full control over the movements of their body, jellyfish often drift in currents. They can also be found floating in large groups, known as blooms.
20. Sea Salp
Sea Salps are often mistaken for jellyfish, but in reality, they are more closely related to us humans!
These mysterious creatures move using jet propulsion – contracting their bodies allows water to move through their bodies at a force that propels them forward.
Another interesting trait: Sea Salps reproduce asexually by creating a luminous chain of up to 80 embryos. They also switch genders at several points during their lifetime.
21. Immortal Jellyfish
Is it actually immortal? When faced with the threat of physical harm, sickness, or old age, immortal jellyfish have the ability to revert back to a state of prematurity known as the polyps stage.
An entire colony of genetically similar polyps are formed, eventually budding off in their sexually mature, free-swimming form. This ability makes the immortal jellyfish an important subject in medical research.
22. Hydromedusa Jellyfish
Hydromedusa is a group of transparent jellyfish that displays a wide array of bright bioluminescent colors. For example, this unnamed species of hydromedusa comes in a myriad of iridescent colors!
They have long, thin, curly tentacles that look like coiled snakes – hence their name. However, very few of them actually sting.
23. Sea Gooseberry
Measuring a minuscule 2.5cm, it is truly astounding that the Sea Gooseberry has tentacles that are up to 20 times the length of its body. Though it may look like a jellyfish, the sea gooseberry is actually part of the comb jelly family.
24. Sea Walnut
Also known as the Warty Comb Jelly, this bioluminescent sea creature exists in huge numbers. They possess comb-like organs that radiate a bluish glow, allowing the Sea Walnut to make parts of the ocean glow when they swim in large groups.
Other Transparent Sea Creatures:
25. Pink See-Through Fantasia
A type of sea cucumber, The strange-looking Pink See-Through Fantasia was discovered in 2007 in the Celebes Sea off the coast of Indonesia. Its transparent body carries a pink hue, and its mouth and digestive tract can be clearly seen from the outside.
Though most sea cucumbers are unable to swim, this particular species is capable of doing so using a wing-like collar around its mouth.
26. Spoke Anemone
Sea Anemones are genetically classified as half animal, half plant. This makes the transparent quality of the spoke anemone all the more impressive, as it hints at its ability to survive without photosynthesis.
27. Portuguese Man o’ War
Sometimes known as the Floating Terror, the Portuguese Man o’ War is aptly named, as it delivers venomous stings that cause the death of fish and humans.
In spite of its deadly self-defense mechanism, this translucent sea creature is otherworldly in its appearance. On top of its see-through silhouette, it has a prominent, long bladder that carries a blue, pink, purple or mauve tinge.
The world of transparent sea creatures is vast and exciting, and we hope this list provided some insight into the various forms they take. Many see-through fish remain undiscovered, though academic experts are working hard to learn more about them.
For now, we have to be content with the facts we have. Which underwater sea creature did you like best? Let us know in the comments below and don’t forget to share this article with someone who might appreciate this list!