I don’t think I’ve ever experienced anything like the glassy-looking growth you describe on the snout and head of your seahorse, but my best guess would be that it might be some sort of Myxobacteria (marine columnaris). Myxobacteria infections are often described as a milky white, slimy film that most often develops on the head of the fish. In its initial stages, the plaque that builds up could appear translucent, but as additional layers of the bacteria build up in a haystack fashion, the slimy coating turns whitish and eventually yellowish. Such infections are sometimes referred to as "bacterial fungus," and indeed Myxobacteria infections are often confused with fungus although they are caused by gram-positive bacteria.
Marine columnaris is a highly contagious disease caused by a Myxobacterium (Flexibacter sp.) that corresponds to the columnaris infections so commonly seen in freshwater fish (Basleer, 2000). The bacterium Flexibacter is a long, slender rod-shaped organism (0.5- 1.0 microns in diameter, and some 4-10 microns long) that is easily identified under the microscope by its characteristic gliding motion (Dixon, 1999). They are unusually mobile bacteria. They are very active when observed microscopically, gliding rapidly across the viewing field (Dixon, 1999). This family of bacteria (Cytophaga or Myxobacteria) causes a condition commonly known as columnaris because of their tendency to stack up in columns (Prescott, 2001b). When large numbers of the bacteria pile up, they form distinctive haystacks several layers thick where the infection is heaviest (Dixon, 1999).
These bacteria are typically associated with stress, and columnaris is primarily an epithelial disease that often presents as a grayish white film that spreads over the fish’s skin, particularly on the head region (Giwojna, Nov. 2003). The whitish plaques spread by radial expansion and may penetrate into deeper tissues, becoming yellow or orange due to masses of pigmented bacteria that stack up in columns forming the haystacks that are characteristic of the condition (Basleer, 2000). Columnaris is often described as a milky, slime-like film that can be observed with the naked eye (Giwojna, Nov. 2003).
If caught early and treated promptly, antibacterial compounds are often effective, especially when accompanied by a decrease in water temperature. Some of the effective medications for treating columnaris include oxytetracycline (administered orally) and especially combination sulfa drugs that include trimethoprim or neomycin combined with various sulfa compounds (Giwojna, Nov. 2003).
For more information on Myxobacteria are marine columnaris, see the following discussion on this forum, which covers the condition in some detail, including the recommended treatment regimen:
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If you feel the classy growth on the head of your seahorse could be a Myxobacteria infection, I would recommend treating her just as described in that thread, except that there would be no need to administer the formalin baths in your case, Seagazer.
The only other thing that comes to mind is the possibility of subcutaneous emphysema (external gas bubble syndrome), but that’s a long shot that’s very unlikely. Occasionally the gas bubbles that build up just beneath the skin are all but transparent and look like air bubbles. It’s unlikely for such emphysema to cover over an extensive area of the head such as you describe, but occasionally two or three of the adjacent gas bubbles will coalesce to form a larger growth. But if the glassy growth you observed was due to subcutaneous emphysema, it would be upraised like a blister, and your post mentioned nothing about the growth being bubble like or blisterlike, so so I don’t really suspect you’re dealing with GBS, but I thought I would trot out the possibility anyway since it is often associated with stress, particularly when a seahorse has been transferred to a shorter (i.e., more shallow) aquarium that it has been living in.
I think you are correct that this problem has developed due to the stress your female has been under recently. It is always stressful for a pair-bonded seahorse to be separated from its mate, and it is always stressful for a seahorse to be uprooted and transferred into a strange new environment, so I’m sure your female was quite stressed out following the transfer, as indicated by refusing to feed at first.
Regardless of whatever else you do, I would suggest feeding her with Vibrance-enriched frozen Mysis, since the Vibrance includes beta-glucan as a primary ingredient. The beta-glucan is a potent immunostimulant that combats stress and will boost the female’s immune system and help her recover from this problem. Feeding your seahorses Vibrance-enriched frozen Mysis assures that they get a daily dose of beta-glucan along with their meals.
Best of luck treating your female’s glassy growth, Seagazer, as well as with your plan to segregate the sexes.