Re:Help. She died.

Dear Grant:

Well, sir, when everything is going great and a seahorse suddenly dies for no apparent reason, it’s very difficult to determine what may have gone wrong. Obviously, if there were no premonitory signs or symptoms of the illness, there is no way of knowing what the proximate cause of death actually was without performing a necroscopic examination. I could speculate on the matter, but it would all be pure guesswork.

I can, however, discuss some of the factors that have been known to account for such sudden deaths in the past. For instance, I have seen one or two cases over the years in which healthy seahorses choked to death after accidentally ingesting a foreign object while feeding from the bottom. When this happens, a foreign object of some sort apparently lodges within the tubular snout, disrupting the flow of water over the seahorse’s gills so that it suffocates in a matter of moments. (It appears that the seahorse’s powerful suctorial feeding mechanism is much better at sucking objects into its tube mouth than it is at expelling something it has accidentally snicked up.)

If an episode like this takes place when the aquarist isn’t around to witness the event, he will return to discover to his or her dismay that a perfectly healthy seahorse is now lying dead on the bottom of the tank for no apparent reason. Choking or suffocating on a foreign object this way is an extremely unusual occurrence — as I said, I have heard of only a couple of such instances in all my years — but it is one more reason to train your seahorses to eat from a feeding trough of a some sort rather than slurping up frozen Mysis from the sand or gravel.

Mysterious deaths from asphyxiation can also occur in seahorses for reasons other than choking. For instance, hypoxia due to low oxygen levels or high carbon dioxide levels has been known to kill seahorses suddenly and without warning. This often tends to happen overnight when dissolved CO2 naturally rises as the O2 levels are dropping due to the reversal of photosynthesis.

As you know, while they are photosynthesizing during the day, zoanthellae and algae consume CO2 and produce O2, but at night, in the absence of light, this process is reversed and the photosynthetic organisms consume O2 and give off CO2 instead. Seahorse setups in general are susceptible to such problems because hobbyists are often so conscious of their seahorses’ limited swimming ability that they tend to leave their aquariums undercirculated. Poor circulation and inadequate surface agitation can lead to inefficient oxygenation and insufficient offgassing of carbon dioxide.

Seahorses are more vulnerable to low O2/high CO2 levels than most fishes because of their primitive gills. Unlike most teleost (bony) fishes, which have their gills arranged in sheaves like the pages of a book, seahorses have rudimentary gill arches with small powder-puff type gill filaments. Seahorses are said to have "tufted" gills because they appear to be hemispherical clumps of tissue on stems. Their unique, lobed gill filaments (lophobranchs) are arranged in grape-like clusters and have fewer lamellae than other teleost fishes. Because of the difference in the structure and efficiency of their gills, seahorse are unsually vulnernable to hypoxia when CO2 levels are high and/or O2 levels are low.

Most deaths due to hypoxia occur when the water pump or filter fails during the night, or there is a power outage overnight when the aquarist is unaware, cutting off the filtration, water circulation, and aeration of the aquarium with devastating results. But there are also a number of other factors that affect the levels of dissolved oxygen in the aquarium, and asphyxiation in seahorses can also occur when there has been no equipment failure.

For instance, heat stress due to a summertime heat wave can rapidly deplete the oxygen levels in a poorly circulated seahorse tank. It’s important to remember that the warmer the water, the less dissolved oxygen it can hold. Elevated water temperatures increase the metabolism of your seahorses, and therefore their consumption of oxygen, at the same time that the rise in temperature is reducing the amount of dissolved oxygen in the water. That creates a dangerous situation for seahorses and may well result in respiratory distress and rapid, labored breathing, as well as contributing to asphyxia under certain circumstances.

There is also an inverse relationship between salinity and dissolved oxygen. The higher the specific gravity or salinity, the less dissolved oxygen the water can hold. By the same token, the lower the salinity or specific gravity, the more dissolved oxygen the water can hold. Sometimes the specific gravity in a seahorse tank can creep up unbeknownst to the aquarist due to evaporation of the aquarium water, and the higher the specific gravity gets, the lower the dissolved oxygen levels in the aquarium will be.

A combination of these factors can be downright deadly. If a heavily planted tank is running too warm and if the specific gravity or salinity of the aquarium has risen higher than the suggested range (1.024-1.025), and the tank is undercirculated, that can sometimes be a recipe for disaster. The oxygen levels in the aquarium will be reduced as a result, and when the lights go off and photosynthesis ceases in a heavily planted aquarium, the oxygen levels will be further depleted while the CO2 levels are rising. In some cases, this can wipe out a tank full of healthy seahorses literally overnight, particularly if the tank is well stocked and houses several seahorses.

Such potential problems with hypoxia are sometimes exacerbated by a transient ammonia or nitrite spike following a heavy feeding. Such spikes are often difficult to detect with test kits because they normally clear up within several hours following the feeding. But despite their transitory nature, they may already have done their damage in the interim by affecting the seahorse’s blood and making it difficult for them to get enough oxygen. This happens because some of the hemoglobin in the red blood cells of the seahorse is converted to methhemoglobin when it is exposed to nitrogenous wastes such as the nitrite and ammonia, and methhemoglobin cannot transport oxygen. So if there is a spike in the nitrate or ammonia levels in your aquarium following a heavy feeding, impairing the ability of the seahorses to transport oxygen through their bloodstreams, at the same time that the dissolved oxygen levels are falling and CO2 levels are rising due to the sort of factors mentioned above, seahorses are in danger of asphyxiation.

In short, Grant, if your water temperature is running on the high side, your seahorse system is undercirculated or overstocked, or the salinity has crept up higher than normal and/or there may have been an ammonia or nitrite spike following the last feeding of the day, it’s possible that your female could have asphyxiated overnight. But I don’t believe that’s a strong possibility, since your Biocube should have excellent water circulation — perhaps too much water flow, if anything — so I don’t think your seahorse asphyxiated and it’s extremely unlikely that it choked to death either.

Rather, I suspect that an acute illness may have killed your female. That’s not at all uncommon when a peracute/acute illness involves the seahorse’s respiratory system or an infection become systemic. Such unusual events can kill a seahorse literally overnight without any premonitory signs. Hobbyists usually refer to this phenomenon as "Sudden Death Syndrome," although in most cases the unfortunate seahorse has actually been ill for quite some time before its demise. Its death seems sudden because the infection had been spreading internally, or the parasites had been spreading within its opercular cavities, with no outward obvious symptoms.

For example, acute or peracute infections of a protozoan parasite (e.g., Uronema species) can sometimes cause sudden death in seahorses. Gill flukes and gill parasites such as these can be difficult to detect at first in seahorses because their gills are covered by the opercula with only a small pore or opening that acts as an exhaust port for the water that is pumped over the gills. The numbers of these parasites can build up quickly within the seahorse’s enclosed gill chambers and cause death by smothering with little outward signs of a problem. But in the case of gill parasites, the infestation typically causes respiratory distress, panting, huffing, etc., and you reported no such breathing difficulties. So we can probably rule out an acute or peracute Uronema infection or a problem with gill flukes or gill parasites, in this case. That makes me think that bacterial septicemia is more likely to have been involved, but as I said, that’s pure guesswork and speculation on my part.

An acute or peracute bacterial infection of some sort is the most common cause of SDS. When septacemia results from such infections, they can kill quickly with no apparent symptoms or signs of trouble. Outwardly, the seahorse seems to be fine, but all the while the infection is spreading internally, hidden and deadly. When such infections take hold in the bloodstream and become septic, they can cause death within a matter of hours.

So my best guess is that your seahorse developed an acute infection of some kind, Grant. As to what caused the infection, it could be anything that impaired the immune system of the seahorse or suppressed its immune response, leaving it vulnerable to disease. In the aquarium, this is usually some form of stress, so I’m going to run through the usual aquarium stressors with you that are often associated with disease outbreaks, for whatever that’s worth, sir.

Disease-causing (pathogenic) bacteria are opportunistic invaders that are normally present in low numbers but don’t cause problems until the fish is injured, stressed, infested with parasites or otherwise weakened (Indiviglio, 2002). They will then take advantage of the overtaxed seahorse’s impaired immune system and reproduce extremely quickly, causing a variety of illnesses and problems (Basleer, 2000). Some of these are specific to seahorses, such as snout rot and white tail disease, and others are common to all fishes, such as Mycobacteriosis or popeye.

A bacterial infection almost always indicates that there is another problem that is stressing the fishes and weakening their immune response (Indiviglio, 2002). In addition to treating the infection itself, the hobbyist must also identify and correct the underlying problem in order to restore health. Check your water quality and aquarium parameters. A water change and general clean up are usually a good place to start.

One of the best ways to prevent bacterial infections and other disease problems is to provide them with a stress-free environment. Many of the parasites and pathogens that plague our pampered ponies are ubiquitous — present in low numbers in most everyone’s systems or within the seahorse’s body itself (Indiviglio, 2002). As a rule, healthy fish resist such microorganisms easily, and they only become a problem when seahorse’s immune system has been impaired, leaving it susceptible to disease (Indiviglio, 2002). Chronic low-level stress is one of the primary factors that suppresses the immune system and weakens the immune response, opening the way to infection and disease (Indiviglio, 2002). Long-term exposure to stressful conditions is very debilitating. Among other effects, it results in the build up of lactic acid and lowers the pH of the blood, which can have dire consequences for seahorses for reasons we’ll discuss later.

When disease breaks out in an established aquarium it is therefore generally an indication that something is amiss with your aquarium conditions. A gradual decline in water quality is often a precursor of disease (Indiviglio, 2002). Poor water quality is stressful to seahorses. Prolonged stress weakens their immune system. And an impaired immune system leaves the seahorse vulnerable to bacterial, viral, and fungal infections to which healthy, unstressed seahorses are immune. As if that weren’t bad enough, there are a number of environmental diseases that are caused directly by water quality problems.

With this in mind, it’s important to review the most common stressors of captive seahorses. These include the design of the aquarium itself. A poorly designed seahorse setup that lacks adequate cover and shelter, or has too few hitching posts, will be stressful to the occupants (Topps, 1999). Seahorses are shy, secretive animals that rely on camouflage and the ability to conceal themselves for their safety and survival. A sparsely decorated tank that leaves them feeling vulnerable and exposed will be a source of constant stress (Topps, 1999). The seahorse setup should have plenty of secure hiding places so they can conceal themselves from view completely whenever they feel the need for privacy. It should be located in a low traffic area away from external sources of shock and vibration.

Needless to say, rapid fluctuations in temperature, pH, salinity and other aquarium parameters must also be avoided. A large aquarium of 40 gallons or more provides much greater stability in that regard than does a smaller setup. The greater the water volume in the aquarium and sump, the more stable the system will be.

Heat stress is especially debilitating and dangerous for seahorses due to a number of reasons (Olin Feuerbacher, pers. com.). For one thing, elevated temperatures can have a very detrimental effect on the immune system of fishes. This is because many of the enzymes and proteins involved in their immune response are extremely temperature sensitive (Olin Feuerbacher, pers. com.). Some of these protective enzymes can be denatured and inactivated by an increase of just a few degrees in water temperature (Olin Feuerbacher, pers. com.). So when seahorses are kept at temperatures above their comfort zone, their immune system is compromised and they are unable to fend off diseases they would normally shrug off.

At the same time heat stress is weakening the seahorse’s immune response, the elevated temperatures are increasing the growth rate of microbes and making disease organisms all the more deadly. Research indicates that temperature plays a major role in the regulation of virulence genes (Olin Feuerbacher, pers. com.). As the temperature increases, virulence genes are switched on, so microorganisms that are completely harmless at cooler temperatures suddenly become pathogenic once the water warms up past a certain point. Thus both the population and virulence of the pathogens are dramatically increased at higher temperatures (Olin Feuerbacher, pers. com.).

This is true of Columnaris and certain types of Vibrio. At cool temperatures these bacteria are relatively harmless, but at elevated temperatures they become highly contagious, virulent pathogens that kill quickly.

In short, it’s doubly important to keep seahorses at the proper temperature. Because of the reasons mentioned above and the fact that water holds less and less dissolved oxygen as it warms up, seahorses generally tolerate temps at the lower end of their preferred range much better than they handle temperatures at the upper limit of their range.

Incompatible tankmates are also stressful for seahorses. This includes not only aggressive, territorial fishes and potential predators but also inoffensive species that are restless, active fishes. Seahorses may be uneasy around fishes that are always on the go, swimming tirelessly back and forth.

Other common stressors for seahorses include overcrowding, overfeeding, stray voltage, and a host of issues related to water quality: ammonia or nitrite spikes, high nitrate levels, inadequate circulation and oxygenation, high CO2 levels and low 02 levels, low pH, etc., etc., etc (Giwojna, Jun. 2002).

Those are my thoughts on the matter, Grant. I suspect that your female seahorse was stressed for some reason or another and succumbed to an acute bacterial infection as a result. I know that’s a rather vague and generalized assessment that’s none too helpful, but, under the circumstances, that’s about all that can be said.

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Best of luck finding the right seahorses for your Biocube, Grant.

Respectfully,
Pete Giwojna