Can I keep phyllidiids in the aquarium?

January 4, 1999
From: Rob See

I am an aquarist in Brisbane, who has just recently caught an interesting nudibranch in Pumicestone passage, off Golden Beach, Caloundra. I am really quite taken with these animals, and have been surfing the net for information on the little critters. Recently I saw a page that told me that nudibranchs do not live very long in aquariums, since they have a highly specialized diet. This has caused me some concern, not only because of my new friend, but also because today I forked out $18.95 for a Phyllidia varicosa. Could someone please clarify this for me as I am somewhat worried
Thanks in advance
Rob See

See, R., 1999 (Jan 4) Can I keep phyllidiids in the aquarium?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Rob,
Yes you are right about nudibranchs having very specific diets. Often you need to know the exact species they feed on - a close relative may not do. Often they will survive in aquaria for some weeks without food but it's probably not a very happy life for them. There are keen aquarists, who are also divers, who try and find what their nudibranchs eat and try and keep a supply of the food alive in their aquarium as well. This may require regular replacement of the food for often it (sponge, hydroid etc) is as difficult to keep alive as the nudibranch. If you know what nudibranch you have we may be able identify its food for you.

The short answer to your second question about keeping Phyllidia varicosa in aquaria is DON'T!
All phylliids protect themselves by taking chemicals from the sponges they feed on and refine them into particularly nasty terpene molecules with attached isonitriles. You don't need to know the chemical details but I have opened a door into a room in which I have kept phyllidiids overnight to be met by an acrid eye-watering atmosphere filling the room. Keeping phyllidiids in aquaria is a pretty sure way of killing other things in your tank within a short period. Experiments with P. varicosa have shown that, when disturbed, they secrete a poisonous mucus capable of killing fish and crustaceans in an aquarium (Johannes, 1963). Gunthorpe & Cameron (1987) also described the toxic qualities of three Phyllidia species (P. elegans, P. nobilis and P. ocellata) from Queensland waters.

Have a look at the pages on the Forum where various aspects of nudibranch biology are discussed, in particular those dealing with colour and defence, including Defensive mucus, mimicry and Phyllidiella pustulosa. Phyllidiids are one of the few groups of nudibranchs that are commonly seen during daylight hours. We now know that they are safe from fish predation because of the distasteful chemicals they secrete through their skin.

Gunthorpe, L. & A.M. Cameron, 1987. Bioactive properties of extracts from Australian dorid nudibranchs. Marine Biology, 94: 39-43.
Johannes, R.E., 1963. A poison-secreting nudibranch (Mollusca: Opisthobranchia). The Veliger, 5(3): 104-105.

Bill Rudman.

Rudman, W.B., 1999 (Jan 4). Comment on Can I keep phyllidiids in the aquarium? by Rob See. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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