Reply To: Young Male Seahorse Off His Food, Hiding, and Darkened Color

Pete Giwojna

Dear Tamra:

I’m very sorry to hear that you lost your juvenile male, and that your juvenile female is also affected and has now stopped eating.

It’s very difficult to diagnose disease problems like this from afar, when you cannot observe the seahorse personally, have no access to clinical tests or cultures to test sensitivity, and cannot take samples for microscopic examination. However, I can tell you that pale areas of depigmentation are commonly seen in bacterial skin infections, such as vibriosis. And Vibrio infections are often secondary infections associated with protozoan parasites like Uronema.

Many such pathogens (e.g., Vibrio, mycobacteriosis, Uronema, fungal infections, and even intestinal parasites) are ubiquitous, commonly found in any aquarium system, or sometimes even within the body of the fishes themselves, but are normally present in small numbers and cause no problems for healthy seahorses until something happens that stresses the seahorses, weakens their immune system, or creates conditions that favor the pathogen or trigger its virulence genes.

For example, many species of Vibrio are natural aquatic flora that are present in all aquarium systems. They are opportunistic invaders that normally only get out of hand and cause problems when something tips the balance in their favor (e.g., deteriorating water quality or low dissolved oxygen levels), a wound or mechanical injury gets infected, or something stresses the seahorses to the point that their immune system is suppressed, leaving them vulnerable to disease. They are typically benign and nonpathogenic until something switches on their virulence genes or creates conditions that favor their growth.

In many cases, it’s an environmental problem that triggers a disease outbreak, such as a spike in the ammonia or nitrite levels, a drop in dissolved oxygen levels due to overcrowding and a lack of aeration/surface agitation, a summertime temperature spike, or some such stressor. The water chemistry in a small, closed-system aquarium can go downhill so quickly and easily. The water quality may have gradually deteriorated in some such respect to the point where it dipped below a critical threshold of some sort and tipped the balance in favor of the pathogens that were present all along. When that happens, the population of opportunistic bacteria can very rapidly get out of control and change from benign to virulent literally like flipping a switch.

Heat stress is a common precursor to many Vibrio infections. For example, here’s what Olin Feuerbacher reports regarding the effect of temperature on bacterial infections. Olin is a marine biologist who is now working as a Molecular Biologist and a member of the research staff at the Arizona Genomics Institute, and who runs a small aquaculture business raising clownfish, gobies, a bit of coral, and all sorts of odd food items including a lot of pods, microalgae, etc. He is also an avid seahorse keeper and has done a lot of research in tropical diseases. His field is marine microbiology, mainly ocean-borne human pathogens, and his specialty has been the Vibrio bacteria!

In short, Olin really knows his stuff when it comes to this sort of thing. Here are his thoughts on bacterial infections in seahorses:

“They (Vibrio infections) start as a secondary infection after either mechanical damage or parasites or cnidarian stings. Once established, they are difficult to control. This is due in part to the fact that they are typically normal flora in all tanks. They are generally benign until they get an opportunity to invade.”

As for the importance of avoiding heat stress when it comes to bacterial infections (or the value of maintaining reduced temperatures when fighting a bacterial infection), this is what Olin has to say:

<Open quote>
It is interesting that you mentioned the elevated temperatures. I think this is a critical factor in a
number of ways. First, elevated temperatures can have many adverse effects on the immune status of many organisms. Many of the enzymes and proteins involved in an immune response are very temperature sensitive. When studying an outbreak of vibriosis in echinoderms during an El Nino event in the Sea of Cortez, I found that several defensive enzymes in the echinoderms were inactivated by a rise of only a few degrees in water temperature.

In addition to the effects on the hosts, water temperature may have very significant effects on the pathogens as well. First, elevated temperature will obviously increase the rate of microbial growth. Perhaps more importantly, recent research has implicated temperature as a major factor in the regulation of virulence genes. When in the cooler pelagic environment, a bacterium wants to conserve energy, so virulence genes will not be expressed since there is probably no host. However, in warmer temps, these genes can be turned on resulting in pathogenesis.

This is especially true for bacteria such as Vibrio species which exist both as normal aquatic flora and as pathogens in many mammalian species with our nice warm digestive tracts etc. One particularly interesting study showed that the coral pathogen Vibrio strain AK1 was completely benign, despite heavy colonization, in corals at one temp (I forget exactly what, I think it was about 25C), but when temperature was raised by 3 degrees, all of the virulence genes in the Vibrio’s pathogenicity island were turned on. This resulted in severe infection and rapid death of the corals. Bad news for aquarists, but I still think this kind of gene regulation is really cool!
<close quote>

In short, Tamra, heat stress is commonly associated with these types of infections, and that may have been a contributing factor in your case with the record temperatures we have seen across the country recently.

In order to help assure that the rest of the seahorses in the main tank are not affected, be sure to make sure that the aquarium temperature remains at 75° F or below, consider installing a good ultraviolet sterilizer with the proper flow rate and dwell time on your main tank, and go ahead and feed the rest of your ponies with medicated Mysis (see my previous post on this discussion thread for instructions on how to prepare the medicated Mysis).

If you are having difficulty keeping the water temperature at 75° F or lower, Tamra, just let me know and I would be happy to provide you with some suggestions for dropping the aquarium temperature.

Good luck.

Pete Giwojna, Ocean Rider Tech Support

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