The Appeal of Sea Slugs and the Challenges of Keeping Them

Sea slugs are sometimes called "jewels of the sea," captivating many divers and aquarium enthusiasts with their vibrant colors and exotic forms. However, keeping them long-term in home aquariums is extremely challenging, and they are known as creatures that pose a formidable challenge for advanced aquarists. This article introduces the ecological appeal of sea slugs while organizing the realistic challenges of keeping them.

What Are Sea Slugs?

Sea slugs belong to the order Nudibranchia (naked gills) within the mollusks and gastropods. As their name suggests, they are a group of snails that lack shells and possess exposed gills. Over 3,000 species are known in the world's oceans, inhabiting diverse environments ranging from tropical and subtropical coral reefs to the deep sea.

Their coloration serves as warning coloration (aposematism). Many sea slugs incorporate nematocysts from their prey into their own bodies and, despite not producing them naturally, possess the ability to repurpose them as a defense mechanism. Some species secrete potassium or acids, which function as toxins against predators.

Protrusions called cerata on the outer mantle function as gills while also creating color gradients. Some species incorporate symbiotic zooxanthellae, enabling them to partially utilize light energy through photosynthesis.

The Greatest Feeding Challenge

The most challenging aspect of keeping sea slugs is feeding. Most species have highly specialized diets, consuming only specific types of sponges, hydroids, bryozoans, or other nudibranchs. Maintaining these food organisms in a tank is nearly impossible, and starvation is the primary cause of failure in sea slug husbandry.

A common exception is nudibranchs of the genus Berghia. They are sometimes introduced for pest control because they feed on Aiptasia (glass anemones), which are a nuisance in aquariums. This species is relatively easy to feed in commercially available aquariums and has a decent track record of success in captivity.

Many sea slugs sold in shops have unclear origins and species identifications, and are often purchased without knowing what they eat. They typically starve within days to weeks of being placed in an aquarium, so impulse purchases should be avoided. Before purchasing, it is essential to identify the species, research its diet, and plan how to ensure a food source.

Water Quality and Environmental Demands