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Sea Hares: Frilly, Fun and Fascinating

We get a lot of really cool stuff in our fish room.  After years and years of seeing the same goodies each week, I love that we get new and interesting species from areas not previously collected from. New crabs, corals, shrimp, fish and other inverts arrive to us each week, but I have to say I’m particularly drawn to the various Sea Hares that show up. I mean, what’s not to like?  These are the equivalent of a cute and fuzzy bunny for your home aquarium!  But they’re more than just an adorable face.  These amazing little guys can play a big role in controlling pesky algae.

The Sea Hares consist of nine genera of family Aplysiidae.  Species of these various genera range in size from under an inch to over 27 inches in length! They are found around the world in temperate and tropical waters. They earned the common name Sea hare for their loose resemblance to a sitting hare or rabbit.  The rolled, erect rhinophores on their heads give these lovely little slugs the silhouette of ears, and their bodies are rather bulbous.  Most species have a thin calcified internal plate or shell in the small mantle cavity to protect the gill and heart.  The cavity is usually covered by variable skin flaps called parapodial flaps.  While most species slide along on their slippery belly, some use their large flaps to “swim” or glide through the water.  Sea Hares are hermaphroditic and may produce clusters, strings, or spirals of eggs in a healthy aquarium.

Sea Hares are all herbivores, feeding on different algaes and cyanobacteria, and making them great workers in a reef or rocky tank.  They may congregate in shallow waters in large numbers when food is abundant. These creatures have a keen sense of smell, (facilitated by their chemoreceptive rhinophores) which allows them to seek out appropriate food in sediments and rock.  They are variable in color and skin texture, but often exhibit a color, texture, or pattern that allows them to blend with the algae they eat.  This camouflage helps to protect them from predators while they lazily graze. Though they look slow, these guys are cleaning machines with big mouths and big appetites!

If the camouflage does not deter predators, these gastropods have a unique secondary defense.  When disturbed, stressed or harassed, they have the ability to release ink from glands in the cavity.  The ink may be white or colored purple or red, and it serves as a noxious smoke screen, deterring predators and allowing the hare to slip away in the confusion.  Their skin also contains other toxins making them unpalatable to predators.

When considering Sea Hares for your aquarium, keep several things in mind.  First and foremost, consider the size of the species you’re interested in.  You’ll need plenty of room and food (algae) for the one you choose, and some species like the Caribbean Dolibrifera are more suited for smaller or delicately arranged tanks.  As for any addition, keep the water quality pristine and be sure not to house sea hares with fish that may pick at or agitate them to prevent inking pollution on the tank. This is more a concern in a small aquarium where the ink would be less diluted should it occur.  Food may be supplemented with live macro algaes and spirulina or sheet algae if your natural algae growth can’t keep up with their appetites.  Sea Hares are rather slow, but heavy and may dislodge loose rock or coral, especially large species in close quarters.

In the right environment, you won’t be disappointed when you add sea hares to your tank. They’re a joy to watch, and a big help if you have nuisance algae.  Choose your chubby new pet with your needs and their’s in mind, and you’re in for a rewarding experience.

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