Re:Dwarf Seahorses for a beginner

Pete Giwojna

Dear hero:

You are very welcome to any and all of the information I can provide that will help to make sure your dwarf seahorse tank a success and ensure that your tour seahorses will thrive.

That is a good thought about using nudibranchs as a form of biological control to eliminate hydroids from your dwarf seahorse setup. There are indeed some nudibranchs that feed upon hydroids and other stinging organisms (cnidarians) such as anemones, and the nudibranchs in general would do just fine in a dwarf seahorse tank that provided them with suitable food.

So your premise is sound, hero: nudibranchs of all kinds will do well with seahorses, even the Pixies or dwarf seahorses (Hippocampus zosterae), providing you are able to provide the proper food for the particular nudibranchs you will be keeping. There will be no competition for food whatsoever between the dwarf seahorses, which need copious amounts of newly hatched brine shrimp (Artemia nauplii) and/or larval copepods for their daily diet, and the nudibranchs, which all have highly specialized diets. The nudibranchs would pose no threat whatsoever to the dwarf seahorses and vice versa.

However, it is very difficult to maintain most species of nudibranchs in the aquarium because it is typically all but impossible to provide them with a suitable diet. They are extremely specialized feeders, some of which feed only on certain types of stinging animals such as hydroids or anemones of a certain sort, and some of which feed only on other nudibranchs. The problem with using the nudibranchs to control the hydroids is that there are about a zillion different types of hydroids, and the diet of the nudibranchs is so specialized that they will often feed on only one genus or type of the hydroids. There is no way of knowing which of the many hydrozoans will appear in your dwarf seahorse tank, so it’s normally not possible to find the particular species of nudibranch that will eat the particular type of hydroids that are causing the problem in your aquarium.

Because it is so terribly difficult to meet the feeding requirements of most nudibranch species in captivity, very few types of nudibranchs are readily available to aquarists. In fact, there are only three different nudibranchs that you are likely ever to see offered for sale. They are the Berghia nudibranchs, which eat Aiptasia rock anemones, the lettuce nudibranch (Elysia crispata), which eats certain types of macroalgae, and the blue velvet sea slug, which eats certain types of flatworms. Unfortunately, none of the nudibranchs that are readily available in the aquarium hobby are predators of hydroids.

You might consider keeping Berghia nudibranchs in your dwarf seahorse tank to eliminate Aiptasia rock anemones. The Berghia nudibranchs are easy to obtain and they would keep your dwarf seahorse setup free of the Aiptasia rock anemones or glass anemones, hero. (You can obtain Berghia nudibranchs bred and raised for controlling Aiptasia at the following website: But you would still want to does your dwarf seahorse tank with fenbendazole (brand name Panacur) to prevent hydroids from becoming established in your dwarf tank, and I suspect the fenbendazole would be very detrimental to nudibranchs of any kind. The nudibranchs are essentially shell-less marine snails, and the fenbendazole is harmful to several types of snails.

Likewise, if you’re going to go with a five-gallon dwarf seahorse setup with lush beds of macroalgae, there is one species of nudibranch that would do very well with dwarf seahorses in a heavily planted aquarium. It is commonly known as the Lettuce Nudibranch.

The Lettuce Nudibranch (Elysia crispata, formerly known as Tridachia crispata, and still usually sold under that name) is a showy, totally innocuous invertebrate that’s a perfect choice for a dwarf seahorse companion. It is green with lavender spots and is covered with extravagant frills and ruffles that look like flower petals on an exotic orchid, but in fact they are the ruffled flaps of tissue (parapodia) that outline each side of the back of this two inch sea slug that lives in the waters of the Caribbean and Florida Keys (Giwojna, 2005). It’s an algae eater that dines on macroalgae such as Caulerpa sertularioides and is one of the few nudibranchs that do well in the aquarium, particularly a dwarf tank with a lush bed of Caulerpa (Giwojna, 2005).

The Lettuce Nudibranch feeds on certain types of Caulerpa and Bryopsis algae in a rather unusual manner. They don’t graze on the macroalgae like a snail as you might expect. Rather, they essentially suck the chloroplasts from certain Caulerpa and incorporate those chloroplasts into their own living tissue in a process known as kleptoplasty. The chloroplasts they have hijacked in this manner will then continue to produce food for the nudibranch via photosynthesis if the aquarium receives enough light. So as long as the aquarium is lighted and contains a thriving colony of Caulerpa macroalgae, the Lettuce Nudibranch will often do very well.

Again, however, hero, you would want to maintain a very low level of fenbendazole in your dwarf seahorse setup with the lush beds of macroalgae, and that could be deadly for the lettuce nudibranch as well. I have never attempted to keep nudibranchs in a tank with Panacur, so I cannot say for sure whether any particular nudibranchs are sensitive to the medication, but I strongly suspect that they would be…

Otherwise, hero, I think it is a splendid idea to set up a five-gallon dwarf seahorse tank with lots of macroalgae and then to set up a separate nano reef tank that can house zoanthids and other live corals.

Here’s hoping that you come up the perfect dwarf seahorse setup for your needs and interests and the perfect way to keep it free of hydroids!

Pete Giwojna

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