“Unless you are able to determine the species of a sea slug and its exact requirements in captivity from a reliable source, I would always recommend against buying any of these animals. Despite the fact that there are many beautiful sea slugs out there, unless you know exactly what you are buying and their feeding requirements, the rule of thumb is to always avoid ever purchasing any sea slug. Sadly, the vast majority of sea slugs are beautiful, but virtually impossible to care for in the aquarium.” – Robert Toonen / Advanced Aquarist 2004 (12)
These wise words were written more than a decade ago and reflect the fact that most nudibranchs are highly specialized feeders which make use of a very limited number of prey species. Many feed only on sponges (especially those most commonly collected for aquarists). Others feed entirely upon particular corals, anemones or hydroids. And then there are the cannibalistic types which dine solely on others in the nudibranch guild. Whatever the case, they’re all carnivores of one kind or another, which means that, invariably, they have no interest in eating whatever algae might be growing on your live rock. That colorful nudibranch you see for sale is almost certainly not going to find anything to eat in your tank… even if your tank is a well-established 1,500 gallon reef aquarium. Unless you have an ample supply of its preferred prey, your nudibranch will inevitably suffer a slow death from starvation.
There might have been a time when this wasn’t common knowledge. I can certainly still remember a local fish store whose manager tried in vain to convince me that the dorid nudibranchs he had for sale would do fine in my reef tank. What’s more, they were supposedly a useful addition that would help keep things clean by scavenging on detritus and algae. There are even videos on youtube which profess the same worthless “knowledge”. One can’t help but wonder where such willful misinformation originates from. Is it pure, unadulterated ignorance… the wishful thinking of a dilettante… or is it maybe just a malicious avarice? Whatever the cause, it’s certainly a black mark on the aquarium trade.
Thankfully, most reputable suppliers now know to avoid stocking these delicate creatures. Industry leaders like Quality Marine and LiveAquaria do a fantastic job of keeping them where they belong… in the ocean. But, while it’s becoming increasingly uncommon to see a dorid nudibranch for sale, they are still regularly collected. Now, perhaps the eternal optimist in you is thinking, “Hey, I’ve got sponges growing on my live rock… maybe they’ll live in my tank?”. To reiterate an earlier point, do you have the particular type of sponge that these species feed on? This is, of course, a mostly rhetorical question, as we generally don’t know which sponges are being preyed upon by these particular nudibranchs, and, even if we did, how confident are you in your sponge identification skills? For example, one species which has been seen in aquariums, Chromodoris coi, seems to feed exclusively on a particular type of purple sponge (Chelonaplysilla violacea)… which you almost certainly don’t have in your tank.
The point in all this is, DON’T EVER BUY A DORID NUDIBRANCH! Once removed from the ocean, these animals essentially become a bouquet of cut flowers. However, unlike flowers, nudibranchs have a fully functioning nervous system to sense the world around them, and, no doubt, they suffer immensely when they are starving to death. So, please, educate yourself and avoid being duped into making such an unethical purchase for your aquarium. And if you do see these for sale, don’t ever try to “save” them by bringing them home. This only creates further economic incentive for retailers and wholesalers to stock them and for collectors to remove them from their rightful home in the ocean. The aquarium trade has more than enough bad publicity without this egregious practice continuing. It’s up to everyone—retailers, wholesalers, aquarists—to end this indefensible abuse of animals.
[Addendum: The original version of this post highlighted the fact that a well-respected retail aquarium store in the US had recently posted video of three dorid nudibranchs that were for sale. Surprising to this author, there seemed to be more readers who objected to my direct criticism of this store’s unethical livestock choice than to the store’s clear exploitation of these lovely little sea slugs, and, so, (against my strong objection) all mention has been removed of the offending party. It is the author’s sincere hope that change comes to the aquarium trade on this issue, but it’s hard to imagine that will be the case when so many are willing to look the other way. Nudibranchs are not colorful ornaments for aquariums, and they deserve to be treated with the same respect we would afford any other coral reef organism.]