It’s very difficult to determine what may be wrong with your seahorses with so little to go on, but for whatever it’s worth, I would be happy to share my thoughts on the matter with you. If there are no open sores or ulcerations, no areas of depigmentation or other signs of a skin infection, no buoyancy problems, and the only obvious symptom is heavy breathing, then my best guess is that either your dissolved oxygen levels are too low or the seahorses are having a problem with some sort of gill parasites.
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, seahorses are particularly susceptible to low oxygen levels and asphyxia.
For starters, consider adding an ordinary airstone to your tank, anchored just beneath the surface of the water. That will add surface agitation, extra aeration, and promote more efficient gas exchange at the air/water interface. Unless you’re quite certain your system already has plenty of water movement, it is also advisable to increase the water circulation, just as Suzanne suggested. If your filter is not adjustable, one simple way to increase the water movement and eliminate dead spots in your aquarium is to add a small powerhead for extra circulation. Seahorses can handle more water movement than most folks realize, and you can always turn it off during feedings. Just screen off the intake for the powerhead as a precaution so it can’t accidentally suck up a curious seahorse.
Aside from your basic water quality tests (ammonia, nitrite, nitrate, and pH), I also recommend that you use a test kit for measuring the dissolved oxygen in your seahorse setup in the future. The reason for this is that a drop in the level of dissolved oxygen is a great early warning indicator that something is amiss in the aquarium, and can thus predict potential problems (and allow you to take corrective measures) BEFORE they become full-fledged disasters. For example, a drop in O2 levels could be an early indicator of overcrowding — a signal that your system has reached its carrying capacity. Or it may merely signal a rise in the water temperature due to a summertime heat wave or indicate that the tank is overdue for a water change and/or a thorough cleaning to remove excess organics and accumulated detritus. Or it could be telling you that your tank is under circulated and you need to increase the surface agitation and water movement.
The point is that checking the O2 levels in your aquarium can alert you to impending problems and allow you to do something about them before they have dire consequences. A drop in O2 levels is often the first sign of a water quality problem and it can tip off the alert aquarist that trouble is brewing before his seahorses are gasping for air in obvious respiratory distress. Checking the dissolved oxygen levels regularly is the next best thing to continuously monitoring the Oxidation-Reduction Potential (ORP) or redox of the water, which is a luxury few hobbyists can afford.
The Tetra Oxygen Test Kit (TetraTest 02) is an adequate liquid reagent test kit for fresh or saltwater with simple color scales for comparing readings that tests for 02 in the range of 2-14 ppm (the optimum dissolved O2 level is 6-7 ppm). It will cost you between $8.50 to $14 depending on where you shop and should be available at any well-stocked LFS. Salifert also makes a nice 02 Test Kit (their 02 Profi-Test) that will run you about $20.
Secondly, it would be advisable to treat your seahorse tank to eliminate any parasites that may be present at which could be contributing to the seahorses’ respiratory distress. Depending on what other specimens are in the aquarium other than your seahorses, this could be accomplished either by treating the tank with an anti-parasitic that won’t impair the biological filtration such as Parinox or by adjusting the salinity of the aquarium to maintain hyposalinity for a period of 6-8 weeks, as discussed below:
Providing your seahorse tank doesn’t include any delicate invertebrates (live corals, shrimp, snails, etc.) that might be harmed by the medication, one good way to eliminate gill parasites would be to treat your main tank with Parinox, which eradicates a wide range of different ectoparasites very effectively, as described below:
USE: For Ich, hexamita, costia, ichthyophthirius, ectoparasites, monogenia, hirudinea, parasitic copepods, argulus, lernaea, anchor worms, fish lice, leeches. Also a protozoacide. Anti-bacterial, anti-parasitic, very wide spectrum.
DOSAGE: Use 1/4 teaspoon per 20 gallons. Treat once a week for 2 weeks. If water changes are done, add back the percentage of medication according to how much water was changed.
You can obtain Parinox online from National Fish Pharmaceuticals at the following URL:
Click here: Fish Medications
As you can see, the medication is effective against all of the ectoparasites and protozoan parasites that attack the gills and skin of fish. It’s a good medication to use in situations like this where were not sure exactly which parasites you may be dealing with Although Parinox is safe for seahorses, it can be hard on crustaceans and certain invertebrates. I don’t believe it will impair your biofiltration at all, so you can use it to treat the main tank and eradicate any parasites it may be harboring providing your tank does not include a lot of sensitive invertebrates. Ideally, it’s best to treat the main tank when there’s an outbreak of parasites to prevent reinfestation, so I would talk to fishyfarmacy over the phone and explain exactly what you have in your tank so they can determine whether or not Parinox would affect any of the other specimens.
If your aquarium include sensitive invertebrates that cannot be moved during the treatment, then you might consider treating the main tank with hyposalinity instead. If you think that might be a better option for you, please let me know right away and I will provide you with detailed instructions explaining exactly how to treat your seahorse tank with hyposalinity safely.
Finally, I would suggest performing a freshwater dip on the seahorse that his breathing heavily as a first aid measure, as explained below:
A freshwater dip is simply immersing your seahorse in pure, detoxified freshwater that’s been preadjusted to the same temp and pH as the water the seahorse is accustomed to, for a period of at least 10 minutes (Giwojna, Dec. 2003). It doesn’t harm them — seahorses typically tolerate freshwater dips exceptionally well and a 10-minute dip should be perfectly safe. Freshwater dips are effective because marine fish tolerate the immersion in freshwater far better than the external parasites they play host to; the change in osmotic pressure kills or incapacitates such microorganisms within 7-8 minutes (Giwojna, Dec. 2003). A minimum dip, if the fish seems to be doing fine, is therefore 8 minutes. Include some sort of hitching post in the dipping container and shoot for the full 10 minutes with your seahorses (Giwojna, Dec. 2003).
If you will be using tap water for the freshwater dip, be sure to dechlorinate it beforehand. This can be accomplished usually one of the commercial dechlorinators, which typically include sodium thiosulfate and perhaps a chloramine remover as well, or by aerating the tap water for at least 24 hours to dissipate the chlorine (Giwojna, Dec. 2003).
If you dechlorinate the dip water with a sodium thiosulfate product, be sure to use an airstone to aerate it for at least one hour before administering the dip. This is because the sodium thiosulfate depletes the water of oxygen and the dip water must therefore be oxygenated before its suitable for your seahorse(s). Regardless of how you detoxify the freshwater for the dip, it’s important to aerate the water in the dipping container well beforehand to increase the level of dissolved oxygen in the water. Many hobbyists leave the airstone in the dipping container throughout the procedure.
Adjusting the pH of the water in the dipping container so that it matches the pH of the water in the aquarium is a crucial step. Ordinary baking soda (sodium bicarbonate) will suffice for raising the pH of the water. If there is too much of a difference in the pH, there is a possibility the seahorse could go into shock during the dipping procedure. Preadjusting the pH will prevent that from happening. If you will are unsure about your ability to accurately adjust the pH in the dipping container, avoid this procedure altogether or be prepared to monitor the seahorse very carefully or shorten the duration of the tip to no more than about 4 minutes.
Observe the horse closely during the dip. You may see some immediate signs of distress or shock. Sometimes the horse will immediately lie on its side on the bottom. That’s a fairly common reaction — normal and to be expected, rather than a cause for concern, so don’t be alarmed if this happens. Just nudge or tap the seahorse gently with your finger if it lies down on its side. Normally, the seahorse will respond to the slight nudge by righting itself again and calm down for the duration of the dip. However, if it does not respond, stop the treatment.
Most seahorses tolerate the treatment well and experience no problems, but if you see continued signs of distress — twitching, thrashing around etc. — stop the treatment.
After you have completed the freshwater dip, save the dip water and examine it closely for any sign of parasites. The change in osmotic pressure from saltwater to freshwater will cause ectoparasites to lyse (i.e., swell and burst) or drop off their host after 7-10 minutes, and they will be left behind in the dipping water. Protozoan parasites are microscopic and won’t be visible to the naked eye, but some of the other ectoparasites can be clearly seen. For example, monogenetic trematodes and certain gill flukes will appear as opaque sesame seeds drifting in the water (Giwojna, Aug. 2003) and nematodes may be visible as tiny hairlike worms 1/16-3/16 of an inch long. Other parasites may appear as tiny dots in the water. Freshwater dips can thus often provide affected seahorses with some immediate relief by ridding them of these irritating pests and can also aid their breathing by flushing out gill parasites.
Best of luck correcting this problem and getting your remaining seahorse healthy again, FERS4REEF.