Re:algae on horse

Dear Scott:

Yes, sir, algae often grows on the exoskeleton of seahorses, typically on their head and neck which are closest to the light source. That’s perfectly normal and nothing at all to be concerned about. In fact, seahorses often encourage algae to grow on them as a protective device to enhance their camouflage, and it’s often best just to ignore any such growth.

That being the case, I usually caution seahorse keepers against trying to physically remove such a coating. Although the algal growth can be unsightly, it is part of the seahorse’s natural camouflage; it can certainly be brushed away, but doing so risks removing the protective slim coat along with the algae which can have harmful consequences. Allow me to explain a little more about the seahorse’s skin and mucosa and the important purpose they serve:

We are all well aware that seahorses can change color to blend into their backgrounds, and that Hippocampus is capable of growing or shedding dermal cirri, which are long filaments and branching extensions of its skin, as called for in order to match its environment. To complete its disguise, the seahorse allows algae, bryozoans and other encrusting organisms to grow on its body, thereby rendering it all but invisible in its natural habitat. In fact, its skin contains polysaccharides which are believed to encourage algal growth, thereby helping it disappear into its surroundings. This vanishing act is so convincing that, even when they are collected by hand seining, seahorses often go undetected amidst the plant matter that accumulates in the net. Unless the collector is really diligent, he will lose a large proportion of his catch simply because many specimens will be overlooked and thrown back with the debris. In short, it’s perfectly normal for algae to grow on seahorses.

The seahorse’s pliant skin or integument is of course its first line of defense against disease. It contains mucus glands, and the slime covering the skin acts as a barrier to ectoparasites and infection. The protective slime can contain antibodies and antibacterial substances, and excessive mucus production is often the first sign of an infection or parasite problem. On the other hand, healthy seahorses often have small bright dots on their heads and torsos, which are actually mucus deposits. These beads of mucus glisten like little diamonds and are a sign of vibrant good health. When handling a seahorse, it’s important to wet your hands first in order to avoid removing too much of the protective slime coat.

Marine fish are always in danger of dehydration because the seawater they live in is saltier than their blood and internal body fluids. As a result, they are constantly losing water by diffusion (osmosis) through their gills and the surface of their skin, as well as in their urine. The mucus layer acts as a barrier against this, waterproofing the skin and reducing the amount of water that can diffuse across its surface.

So, all things considered, many times it’s best just to ignore any algae that happens to grow on your seahorses. Removing it means removing the slime coat and mucous barrier as well, leaving the seahorse susceptible to infection and dehydration. It will secrete more mucous and repair its slime coat over the next day or two, but it will be vulnerable in the meantime.

If the algae growth should become so heavy that it becomes irritating to the seahorse, as indicated by its attempts to rubble or scratch itself against objects to remove the algae, then it can be brushed away very gently using an artist’s camel hair brush or something similar, but in your case I would simply leave it be, Scott.

Best wishes with all your fishes, sir!

Respectfully,
Pete Giwojna