Alternative to Sponges for Hypselodoris bullocki

October 26, 2000
From: John Leventis

I have purchased a Hypselodoris bullocki from my local marine fish dealer, and I believe I have found what it eats. Here is my research.

I have observed my Hypselodoris bullocki feeding on and around the powerhead (a motor used to create water currents) that sucks water to my protien skimmer (an instrument that filters fish waste), as well as other areas of high water flow in my 55 gallon tank. I have observed that it was feeding off of a green hair algae that commonly grows in saltwater aquariums, specifically in areas of fast moving currents (for example, around powerheads). I also know that this algae requires little or no light, since it has also grown in some of the dark areas behind my live rocks.

I have introduced yellow and red branchy sponges into the tank, but it hasn't yet been of any intrest to it. Then again, I am not certain of the exact names of those sponges. The reason I did this was because I have read from another article posted on this site that nudibranchs like mine eat sponges. It also made mention that they introduced a marine sponge food (Angel Formula made by Ocean Nutrition) and the nudibranch was immediately interested. It failed to mention how much, if any, the H. bullocki ate and for how long. It did say that the nudibranch later consumed the hair algae that later grew off the leftover bits; I assume to be the same kind that is in my tank.

My H. bullocki fed on around 6-8 sq. inches of the green hair algae in around 1 hour. How accurate this is, I am not positive. The H. bullocki fed off of the hair algae until it ran out in that area, and then moved on and found more. I can therefore say that it must have an interest in such algae. Whether or not this algae is a staple food for it, I am not 100% positive, but I know that the green hair algae the H. bullocki has been eating is also of great interest and good nutrition to other herbivorous fish and invertebrates. Also, it has been feeding off of it for the past week without signs of malnutrition or inactivity.

I have experimented with other foods to see if it will eat them. I tried to feed it an algae- based flake food, but it failed. I did also notice it trying to lap up some of the diatom masses (diatoms are an brown, quick-growing algae found in every saltwater tank) that has been floating on portions of my tank's water surface for awhile, but let up after it dicovered the green hair algae. Whether or not it was truly interested in it or just testing it, I am not positive.

That is all I have found out for now. I will continue to research and experiment with the Hypselodoris bullocki and other nudibranchia to retrieve more information on their foods and feeding habits. I'll try to keep you posted, but you have to respond. Thank you. By the way, you have a great site and it is a great help to me.
That's all.
John Leventis
Maryland, USA

Leventis, J., 2000 (Oct 26) Alternative to Sponges for Hypselodoris bullocki. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear John,
Thanks for your detailed observations on your Hypselodoris bullocki. I guess the first thing to say is that it is a sponge feeder, and all its relatives are sponge feeders.So how can we interpret your observations? One possibility is that the 'hairs' of the filimentous green algae are acting as filters and becoming coated with a layer of organic matter which attracts the nudibranch. A more likely explanation, I'm afraid, is that you animal is starving. To get to your fish shop in the eastern USA it would have been collected somewhere in the Pacific and then shipped to the USA. At a minimum I would suspect it has been without real food for 2-3 weeks. Hypselodoris feeds by rocking its rasping tongue-like radula out of its mouth where it scrapes off a layer of food sponge. This is a fairly rhythmic activity which you can often see these animals doing as they crawl along the side of an aquarium.

I wish I could say that it looks like they do eat filamentous algae for food, but I suspect that your animal is operating on 'automatic' whether what it is eating is suitable food or not. In spite of my views, please keep us informed of your animal's progress. There is always the possibility you have made a great discovery.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Oct 26). Comment on Alternative to Sponges for Hypselodoris bullocki by John Leventis. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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