Vibrio and calcium

Dear Nicole:

It is very difficult to determine what triggered a particular outbreak of Vibriosis, but I would be happy to discuss some of the contributing factors that are involved in many such cases.

First of all, Nicole, it’s important to understand that many of the pathogens and parasites that commonly playing seahorses and other marine fish are ubiquitous, present in low numbers throughout the aquatic environment, even under sanitary conditions in well-maintained aquariums with healthy fish. Although the fish are exposed to these ever-present potential pathogens, they remain healthy because their immune systems are able to effectively overwhelm the low level of the pathogens they encounter and because the sanitary conditions do not favor the pathogens or infectious organisms.

However, if something impairs or suppresses the immune system of the seahorses, or if the conditions change so that they are more favorable to the pathogens, then the infectious organisms can overwhelm the immune system of the seahorses, and they will fall ill. That is how many primary infections in seahorses and other marine fish get started.

That’s the case with many of the common diseases in seahorses, Nicole. This includes Vibrio infections, mycobacteriosis, Uronema, fungal infections, and even intestinal parasites. These pathogens 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 lots of pods, microalgae, etc. He is also an avid seahorse keeper and has done a lot of research in tropical diseases. He is a grad student working on 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:

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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 the Vibrios 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!
Olin
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That’s the rundown on Vibrio infections, Nicole, and some of the things that can lead to an outbreak in an aquarium.

Offhand, I don’t know of any link between calcium deficiency and vibriosis, except that inadequate bioavailable calcium could be an indication of deteriorating water quality, which in turn could create stress and/or more favorable conditions for the pathogen.

If you have any concerns about soft plate disease affecting seahorses or pipefish in your aquarium system, Nicole, it can easily be prevented as explained below:

Soft Plate Disease:

Seahorses and pipefish that receive a diet deficient in calcium are prone to “soft plate” syndrome, which is a progressive disease characterized by decalcification of the bony plates that fuse together to form the exoskeleton (Greco, 2004). In the olden days, this was often a problem with seahorses that were fed a diet consisting solely of Artemia (Greco, 2004). We now know that brine shrimp (Artemia spp.) contains inadequate levels of calcium and an imbalanced ratio of calcium to phosphorus, making it unsuitable as a staple diet even when enriched (Greco, 2004).

Seahorses afflicted with soft plate syndrome exhibit shortened lifespans, decalcification of their exoskeleton, and poor survival rates amongst their fry (Greco, 2004). Pregnant males face the greatest risk of soft plate. Seahorse fry are known to incorporate calcium provided by their father into their skeletons during their embryonic development, so when a gravid male is deficient in calcium, his rapidly growing offspring typically suffer high mortalities due to a condition akin to rickets in human children.

Fortunately, this debilitating condition is easily prevented by providing seahorses with adequate levels of bioavailable calcium either in their diet or in the aquarium water itself (minerals can be obtained by fish directly from the water; Greco, 2004). For example, I have never heard of a case of soft plate in a seahorse kept in a reef tank that received Kalkwasser (calcium hydroxide) via an automatic doser or regular supplementation of bioavailable calcium. Nor have I even seen this condition in seahorses that received a stable diet of enriched frozen Mysis relicta.

This is what I typically advise home hobbyists regarding calcium, Nicole:

Calcium (Ca):
Natural Seawater Value = 400 mg/L
Acceptable Range = 350 to 450 mg/L
Optimum Level = 350 – 400 mg/L (up to 500 mg/L in well-stocked reef tanks)

Calcium is a very important element in the water in any marine aquarium and is a vital element in reef tanks. Along with carbonates and bicarbonates, it is required by calcifying organisms such as stony corals, snails and other mollusks, coralline, Halimeda and other calcareous algae, and certain sponges (Trevor-Jones, Apr. 2003). Calcium is a critical parameter for coral growth in reef aquariums, and chronically low levels will cause coral mortality and loss of coralline algae and other invertebrate species. Calcium reserves must therefore be replenished on a regular basis. Regular water changes may achieve this, but reef keepers may require the addition of biologically available calcium to maintain adequate levels (Trevor-Jones, Apr. 2003). Seahorse keepers should be aware that brooding males provide calcium to the developing fry in their pouches, which the embryos probably incorporate into their skeletons. Deficiencies in calcium could thus adversely affect your seahorses’ reproductive success and the health of the fry. In fact, seahorses that receive a diet deficient in calcium often suffer from decalcification of their exoskeleton, a debilitating condition commonly known as “soft plate” disease (Greco, 2004).

Best of luck resolving your issues with vibriosis, Nicole.

Respectfully,
Pete Giwojna, Ocean Rider Tech Support