I’m sorry to hear that your store-bought seahorses have developed a problem. It sounds like you are dealing with an outbreak of white spot disease (Cryptocaryon irritans), which is a common problem with new arrivals obtained from the LFS where they are often exposed to the parasites.
Cryptocaryon is commonly known as saltwater ich or white spot disease. It is caused by a protozoan parasite that burrows into the skin and gills of its host and is one of the most common diseases of marine fishes. Most hobbyists who keep saltwater fish are all too familiar with Cryptocaryon. In the confines of the aquarium, massive reinfection of these parasites occurs, making Cryptocaryon deadly if left untreated.
In seahorses, it often occurs as a masked infection. The bony exoskeleton and protective slime coat of Hippocampus gives the seahorse limited immunity from the burrowing trophonts, so the telltale white spots may never show up (or may be visible only on the unarmored fins). But the parasites can still freely invade the seahorse’s gills, with deadly results.
In addition to treating your tank with copper sulfate, I would recommend administering a daily freshwater dip to provide your seahorses with immediate relief. Here’s an excerpt on Cryptocaryon from my new book (Complete Guide to Greater Seahorses) that discusses various treatment options:
Cryptocaryon irritans (Saltwater Ich, a.k.a. White Spot Disease)
Cryptocaryon is another protozoal parasite that invades the gills and burrows into the skin of marine fishes, including seahorses. The life cycle and modus operandi of Cryptocaryon are very similar to that of Amyloodinium ocellatum, so it should not be surprising that it also produces strikingly similar symptoms. Infected fish show labored breathing, excess mucus, and scratch themselves against objects. Along with the characteristic pinhead-sized white spots and excess mucus production, affected fish sometimes show cloudy eyes and secondary infections (Basleer, 2000). The latter can result in skin rot and fin rot accompanied by red or pale patches on the body of the fish (Basleer, 2000).
The white spots seen on infected fish are the adult stage of the parasite, known as trophonts (Basleer, 2000). When they mature, they fall off the fish and encyst themselves. The encapsulated parasites are known as tomonts (Basleer, 2000). Well protected within these cysts, the tomont stage cannot be killed by any medications. The encapsulated tomonts divide into hundreds of daughter cells, which develop into small, ciliated, free-swimming parasites, called tomites (Basleer, 2000). When the cysts rupture, the motile tomites swarm out to seek a new host. In the aquarium, they reinfect the same fishes, and bore into the mucosa of the skin, gills, and fins of their hapless hosts. Once embedded in the tissue, they mature into typical trophonts, appearing as pinhead-sized white spots on most fish, and start the cycle of infection all over again (Basleer, 2000). It is these heavy infestations that can overwhelm even healthy fish.
The free-swimming stage of their life cycle is Cryptocaryon’s one great weakness. The motile tomites are vulnerable and exposed. Ozone or UV can destroy them, they can be killed by all the usual chemotherapeutic agents, and they explode (lyse) when exposed to freshwater and low salinity. It is therefore the tomites that the aquarist must target when treating Cryptocaryon.
At 100x magnification, Cryptocaryon parasites can easily be identified in skin and fin smears. They appear as large, dark, bell-shaped or conical organisms measuring about 350-400 micrometers in diameter (Basleer, 2000).
Outbreaks usually coincide with the introduction of new specimens or environmental insults such as rapid temperature fluctuations (heat stress or chilling), ammonia or nitrite spikes, or a sharp drop in pH (Basleer, 2000). The first step toward treating Cryptocaryon is therefore to restore water quality. Check your aquarium parameters and administer water changes as needed.
The traditional treatment is similar to that for Amyloodinium. Combination drugs such as formaldehyde/copper sulfate or formaldehyde/malachite green are often more effective than copper alone (Basleer, 2000). Medication must be maintained at therapeutic levels for at least 8-10 days and the best results are obtained when daily freshwater dips are a part of the treatment regimen (Basleer, 2000). The entire tank should be treated and methylene blue can be added to the water to aid the breathing of the fish (Basleer, 2000). Be aware that these medications will impair your biofilter and kill your invertebrates!
Cryptocaryon is normally easily distinguished from Amyloodinium by the fact that the embedded parasites produce pinhead sized white spots that are much larger that the tiny dust specks that indicate Marine Velvet. However, the telltale white spots are again often entirely absent when seahorses are the hosts, leaving the seahorse keeper in a quandary when it comes to diagnosis and treatment.
Freshwater dips and baths are a form of osmotic shock therapy. The abrupt change in salinity when going from normal strength saltwater to freshwater causes water to move into the bodies of the parasites via osmosis until they rupture (lyse) or burst. Seahorses normally tolerate an 8-10 minute dip in freshwater very well, providing the dipping water has been pre-adjusted to the same temperature and pH as the aquarium, and a daily freshwater dip will provide the affected seahorses with immediate relief and hasten their recovery from this disease.
Freshwater Dip Instructions
A freshwater water 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).
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 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 experienced no problems, but if you see continued signs of distress — twitching, thrashing around etc. — stop the treatment.
After you have completed the dip and returned the seahorses to the aquarium, save the dip water and examined 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 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 resolving this outbreak of white spot disease, Nigel. Hopefully your seahorses will be feeling much better soon.