Saltwater Ich, also known as Marine White Spot Disease, is caused by the parasite Cryptocaryon irritans. The term “Ich” is a generic carry-over from the freshwater parasite Ichthyophthiriius. Since both parasites cause white spots on the fish, the disease is universally called Ich, even though they are different parasites. A saltwater ich outbreak in a marine or reef aquarium is a serious matter. In aquariums and aquaculture environments, fish loss due to an ick outbreak can be very high. Let’s take a closer look at this parasite and learn how to avoid it and if necessary, treat a marine ich outbreak.
What Does Saltwater Ich Look Like?
The cryptocaryon parasites are microscopic, which means you can’t really see them with the naked eye. As aquarists, what we notice first are the symptoms of the parasitic infestation on our saltwater fish, which typically includes: ragged fins, scratching behavior (the fish scratching itself erratically) on rocks or sand, and of course the hallmark white spots or nodules on the gills, fins and body of the fish.
But just because you don’t see white spots on a fish’s fins or body doesn’t mean that the fish is not infested with saltwater ich. Sometimes the ich parasites infest primarily in the gills, showing no white spots or other outward symptoms, so it might be worth trusting your gut instincts if you are pretty sure the fish is sick, based on your observation of their behavior.
If you just aren’t sure, you may want to try doing an internet search for images of saltwater tank to get a feel for how it looks when different species of fish are infested–here is an interesting link for that:
Marine White Spot Disease: Know Your Enemy!
Before entering a battle, it is important to know who or what you are up against. It is the same way with fish diseases. In order to understand how you have to fight marine ich, it is helpful to take a moment to understand the life cycle of ich.
Saltwater ich has a complex multi-step life cycle.
- The feeding or trophont stage is where the parasites are swimming around under the skin and gills of the fish. The parasites eat cells and fluids, damaging tissues and leaving the fish in a weakened state. Here is where you may see the white spots and other outward symptoms. Ich treatments generally do not affect the trophonts because they are protected under the skin of the fish.
- Once the Trophonts are fattened up, they leave the fish as a protomont.
- Protomonts lose their ability to swim, fall to the bottom of the tank and in a few hours becomes a tomont. The parasite becomes a hardened cyst, like an ich egg, waiting to hatch. The tomont is a ticking time bomb full of nasty little parasites. What was once a single ich parasite, now divides again and again, storing up hundreds of new parasites called tomites.
- After a number of days or even weeks, the cyst opens up and the infective parasites are released as free-swimming theronts, seeking to attack your fish. This is really the primary stage that ich medications are effective against the parasites. The thereonts have about six hours to find a fish and burrow into the skin, becoming a trophont. Then the cycle begins again. Depending on the severity of the outbreak, an aquarium or shop full of marine fish can be wiped out due to the reoccurring nature of the parasite life cycle.
Preventing and Treating Marine White Spot Disease
The best way to protect your saltwater fish tank or reef aquarium is prevention. Prevention means keeping ich-infested fish out of the aquarium. This is done with a quarantine tank. The idea behind quarantine is to isolate a new fish, observe it for several weeks, ideally one month to make sure the fish is healthy. A quarantine aquarium can be as simple as a ten or twenty-gallon tank with a heater and filter. If the fish is carrying a hidden ich infestation it will likely show up during quarantine. If it does, your quarantine tank helps you keep from infesting your main aquarium and also provides you with a small, safe location to treat your sick fish.
There are several ways to treat ich in a quarantine aquarium.
The water change method to treat saltwater ich
One method involves making 50% water changes every day for two weeks, paying careful attention to being able to siphon off anything lying at the bottom of the tank. Which means you must have a bare bottom tank if you have any hope that this is going to work. If you remember back to the third step in the lifecycle (listed above), the protomonts fall to the bottom of the aquarium and become tomonts. The idea here is that since you are vacuuming up the bottom of the tank, each and every day, you should (in theory) be able to remove all of the tomonts/cysts before they become problems. Of course, since a single parasite can explode into many copies of itself in a short period of time, this method certainly does have an Achilles heel. If you miss even a few, you may not eradicate the problem.
Hyposalinity to treat saltwater ich
Another non-chemical treatment for saltwater ich is called hyposalinity. One of the forces of chemistry that every aquatic creature must face is called osmotic pressure. Osmotic pressure is the principle behind reverse osmosis water purification in your RO/DI filter (if you have one). You can employ osmosis to your advantage to destroy saltwater ich by lowering the salinity of the water to a level that is close to freshwater (close, but not quite). Please note that you should only do this with hardy marine fish species, not with any invertebrates at all.
The hyposalinity method is fairly straightforward. Gradually lower the specific gravity of your aquarium water to 1.009-1.010 or so and keep it there for a few weeks. Monitor your fish for signs of increased stress caused by the change in salinity and stop/reverse the hyposalinity treatment if the fish is under extreme stress. But in many cases, you should be able to lower the salinity without much difficulty.
Once you feel fairly certain you have eradicated all of the ich parasites, slowly increase the salinity to the normal range over a few days to get the fish acclimated to full strength seawater, before placing it in your main aquarium.
The freshwater dip is an old yet effective method against a variety of parasites, including saltwater ich. It is actually a more extreme spin-off of the hyposalinity method. The goal of the freshwater dip is to put the infected fish in complete freshwater for a short period of time (2-5 minutes) to kill off any of the parasites on the outside of the fish.
Fill a bucket with dechlorinated tap water, RO or deionized water. Use a heater to match the temperature to the aquarium. Use a pH buffer to bring the pH to match the aquarium. Be sure to add an air stone to oxygenate the water. Now add the fish to the bucket for two to five minutes. Some fish show no reaction while others sink to the bottom. There is no reason to panic, this is normal. If you are observing extreme stress, it is probably best to return the infested fish to a quarantine tank and treat the infestation a different way, but if your fish handles the treatment reasonably well, you may be able to kill off enough of the parasite for this method to work. Some aquarists have found wrasses and firefish to be sensitive to freshwater dips. Use caution and watch the fish and don’t push your luck if your instincts are telling you the fish is not holding up.
Two popular commercial treatments for saltwater ich are copper (cupramine) and formalin. These treatments can be challenging because they are toxic to both ich and your sick fish—so you have to be very diligent about following the manufacturer instructions and making sure you do not over-dose the fish. Under-medicating the aquarium carries the separate risk that you won’t even cure the infestation. So medication can be a bit tricky.
The magic cure for saltwater ich
Haha, that was a dirty trick, for me to use a headline like that, but I regret to inform you that there is no magic cure for saltwater ich. So don’t believe the hype, especially if the product claims to be completely reef safe, organic, recycled, or has other slick marketing (and this is coming from a marketer).
I don’t want to bash any products here, but if you have any doubt, I encourage you to try and find out from others in the hobby if the miracle elixirs work. Make sure you ask enough people to get a few data points.
Am I missing anything? How have you treated saltwater ich in your aquarium?