10 Weird Sea Creatures You Can Actually Keep In Your Aquarium

If you’re a regular FantaSEA blog reader, you’ll know our oceans are brimming with the weird and wacky. But did you also know you can bring some of its most exquisite oddities right into your own home?

From anemone-wielding crabs to a fish that functions as a seeing-eye dog for a blind shrimp (who also happens to have a built-in stun gun), here are 10 weird sea creatures you can keep in an aquarium!

1. Pom-pom crab

It may look like a tiny crustacean cheerleader, but don’t be fooled by its rather adorable looks. The pom-pom crab packs a punch! Those aren’t poms, they’re stinging tentacles. Not the crab’s stinging tentacles, mind you. It didn’t grow them itself—it found and cultivated them.

Crabs in the genus Lybia carry specific species of anemones with potent stinging cells (called nematocysts) on their claws. These anemones serve not just for self-protection, but also come in handy while foraging: the crab uses them to mop up edible bits from the seafloor. Researchers have found it leaves its “pets” just enough food to survive, but not enough for them to become too large to carry.

The cool thing? Due to their small size (less than 1”), pom-pom crabs are suitable for nano aquariums. You can keep one in your home reef with ease, as they mostly feed on detritus and aren’t known to bother their tankmates.

2. Pistol shrimp

These peculiar invertebrates, also known as snapping shrimp (members of the varied family Alpheidae), are well-known mostly for their bizarre ability to cause underwater explosions.

Experiments revealed how it works: when the shrimp snap their oversized front claw shut, they create a tiny vacuum, which can reach temperatures in the thousands of Fahrenheit and quickly knocks out prey or attackers.

If you think a stun gun-wielding shrimp doesn’t exactly sound like an ideal choice for your home aquarium, strangely enough, you’d be wrong. There are hundreds of species, many of which are perfectly suitable as pets. They’re often beautifully colored and sport extravagant, eye-catching patterns.

Oh, and don’t worry if you hear loud snapping noises coming from your tank. Pistol shrimp, unlike the larger and even more overpowered mantis shrimp, can’t break aquarium glass. 

3. Watchman goby

In the wild, the aforementioned pistol shrimp rarely live alone. Although they can clearly fend for themselves, they’re also nearly blind, making them unable to see any danger approaching.

The solution? Using a bottom-dwelling fish as their eyes. Meet the watchman gobies, highly vigilant fish that can alert their shrimp buddies at the slightest sign of trouble. Our favorite is the yellow watchman goby!

Studies have found that the symbiotic goby-shrimp relationship has advantages for both parties. The goby isn’t able to defend itself—it can’t even bite attackers—so it alerts the pistol shrimp using touch when something is wrong.

The shrimp uses its superheated snap and voilà, any predators are forcefully ejected. In return for its watchful eye, the shrimp lets the goby live in its meticulously maintained burrow.

In your aquarium, you don’t have to keep a watchman goby and pistol shrimp together. They both do fine on their own. But if you do, you can brag about having a shrimp with a seeing-eye fish for a pet, and that’s quite hard to beat.

4. Serpent starfish

What’s weirder than a starfish (or more correctly, sea star)? A starfish with thin, snake-like arms that can run across the seafloor, of course!

The serpent starfish normally spends most of its time securely wedged under rocks or buried under the sand. When disturbed, though, it shoots out arms flailing, scurrying back to safety at breakneck speed. It gives me the crawlies, but I can’t deny it’s effective.

If you don’t mind the slightly creepy looks of the serpent starfish, you can keep one in your fish tank. Most starfish are notoriously difficult to keep as pets, because they’re sand sifters that tend to starve in our overly clean aquariums.

Not the serpent: it naturally eats carrion. Just place an offering of seafood bits next to your star’s hide on a daily basis to keep it fat and happy. That’s why it’s also on our list of easiest starfish for the aquarium.

5. Harlequin shrimp

Is it a coral? Is it a praying mantis? Nope, not even close! It’s a harlequin shrimp, among the top contenders for “weirdest sea creatures” in the crustacean category. With their flat, large claws, oversized eyes, and blue-purple polka dot pattern on a white base, these aren’t your average shrimp scampi. 

Impressively, this species’ weirdness doesn’t end with its alien looks. It’s also a very picky eater that refuses to consume anything but starfish legs. Because of these strange eating habits, the harlequin shrimp is often used in the aquarium to combat infestations of Asterina, a tiny starfish species that reproduces very quickly and can overrun entire tanks.

Tip: Love harlequin shrimp? They’re not the only wacky shrimp you can keep in your tank. Have a look at the list of our favorite aquarium shrimp to meet more of these useful oddities.

6. Longhorn cowfish

A member of the family Ostraciidae, the boxfishes, the longhorn cowfish (Lactoria cornuta) looks more like a yellow cube with bull horns than a fish. This omnivorous reef species is naturally found in the Indo-Pacific, where it feeds on algae, single-celled organisms, and select invertebrates.

Longhorn cowfish are a favorite for public aquariums, where their bright yellow color and strange appearance draw attention. They’re also sold in aquarium stores. Aquarists report they’re intelligent, curious, and fascinating to watch as they go about their business!

There are two caveats to keeping longhorn cowfish. Firstly, there’s their size; although they’re usually sold as adorable tiny juveniles, they can reach a length of up to 20″. This means you need at least a 150-gallon tank if you’d like to keep one.

Secondly, these cowfish aren’t the best choice for busy community reefs. Not because they don’t play nice with their neighbors—they’re mostly reef safe and compatible with many calm fish and invertebrate species—but because of the neurotoxin.

A stressed longhorn cowfish, like other boxfish, can excrete the highly deadly pahutoxin through its skin mucus. This is not dangerous to us aquarists, but is said to have the capacity to kill off the contents of an entire tank. Understandable, then, that this species is best kept on its own!

7. Garden eel

Remember being at the aquarium and admiring a large cylindrical tank filled with swaying seagrass? Remember taking a closer look and realizing the seagrass has eyes? If yes, then you’re familiar with the garden eel (Heteroconger hassi), a strange elongated fish that has made looking like a piece of seaweed its principal goal in life.

Garden eels spend their days in a burrow they dig in the substrate when they’re still small. Most of their body never leaves the burrow: the head and neck are the only parts that stick out. It works for them because all they have to do to stay well-fed is open their mouths. This allows them to catch any particles drifting around the current.

If you’d like to keep garden eels as a pet, you’ll need a specialized aquarium with a thick layer of soft substrate. It’s a hassle, but it may be worth it so you can bring some of the oddest the ocean has to offer into your home. 

8. Caribbean dwarf octopus

We’re still missing a photo for this creature! Contact us if you’ve got one we can use (with credit).

Wait, you can keep an octopus as a pet? The answer is yes! Certain species of octopi can do well in a fish tank, provided you don’t mind the cost of buying their favorite meals (loads of shrimp and crab) and their short lifespans (usually under 2 years). They do well in single-species tanks and make for surprisingly interactive pets. 

If you’ve seen the My Octopus Teacher documentary, you’ll understand why these strange molluscs are so amazing. For those who haven’t, let me quickly sum it up.

First off, although they may not look like more than squishy heads with too many arms, scientists have found that octopi are actually extremely intelligent. They can remember things, solve problems, and are real escape artists. Oh, and they can change color, too!

One of the most popular octopus species for the aquarium is the tiny Caribbean dwarf octopus (Octopus joubini). Although it has all the personality of its bigger cousins, it only grows to around 5”, making it much more manageable.

9. Kuda seahorse

Raise your hand if you’ve secretly wanted a seahorse aquarium since you were a kid! The otherworldly seahorse is such an oddball that many of us don’t even realize that they’re actually a species of fish. There’s something about their upright stance and the way they sway in the current that makes them decidedly… un-fishy.

Although a seahorse aquarium isn’t the easiest to maintain, it can be done. Some species, like the kuda seahorse (Hippocampus kuda), can thrive and even reproduce in our home tanks. Just don’t expect your female seahorses to give birth—for some reason, that’s the male’s job. 

10. Frogfish

Let’s go out with a bang, shall we? Meet the frogfish, which doesn’t really look like a frog at all—although admittedly, it doesn’t look much like a fish either. Members of the anglerfish family Antennariidae, these colorful creatures have perfected the art of camouflage.

Some frogfish are covered in hair-like strands that look like sea anemones, while others bear so much resemblance to a sea sponge that it’s hard to tell the difference.

Its looks may be silly, but the frogfish is a natural-born killer. Like other anglerfish, they are ambush hunters. Instead of chasing after their meals, they wait for their prey to approach them. Once a tasty morsel comes close enough, they open their immense mouths and swallow it whole—faster than you can blink. How’s that for silly?

Some species of frogfish can be kept in the home aquarium. They’re not that difficult to care for, but since they consider anything that fits in their mouth a snack, they do best in single-species tanks. 

There you have it: 10 of the weirdest sea creatures that you can keep in your home aquarium. Which one’s your favorite? Got any suggestions for honorable mentions? Be sure to leave a comment below!