White Spot Disease in Saltwater Fish (Saltwater Ich)
Unfortunately, fish are susceptable to a variety of diseases, especially in the aquarium, due to the close proximity of other fishes. One of the most common diseases encountered by saltwater fish is white spot disease. This disease is also known as saltwater ich or marine ich. It is caused by the parasitic protozoan Cryptocaryon irritans. This disease has a similar life cycle and causes similar symptoms as freshwater white spot or ich, but they are caused by different organisms.
If your fish develops white spot you will notice small white spots on your fish's body and fins. The fish will also lose its appetite and may appear to be in respiratory distress (the fish will be breathing at an increased rate). This is because the free-swimming stage of the parasite easily enters the gills and infects them, making it difficult for your fish to breathe. You may also see the fish scraping itself on rocks in an attempt to dislodge the parasites.
The white spots are cysts full of Cryptocaryon irritans. Eventually the cysts open, leaving sores on the fish's body and spilling out free-swimming parasites to infect other fish. This free-swimming form is microscopic in size and can't be seen with the naked eye. The sores left on the fish's body where the cysts were may get infected with bacteria or fungi. If untreated, the fish will die.
Saltwater Ich Treatments
Fortunately, there are treatments available. These treatments are only effective for the free-swimming stage of white spot. Copper based treatments such as copper sulfate will help to eradicate saltwater white spot. Remember that if you have invertebrates in your tank that copper based treatments will kill them. If you use an ultraviolet sterilization unit, the ultraviolet light will also kill some of the free-swimming white spot parasites, while leaving the invertebrates intact.
If only one fish is affected you can remove the fish into a different tank and treat it with copper sulfate. In fact, it is best to remove any affected fish and treat them in a quarantine tank. It takes 14-21 days of copper sulfate treatment to completely irradicate Cryptocaryon from your aquarium. Also remember that copper sulfate kills the inhabitants of live rock.
You can also give your saltwater fish a freshwater bath. The idea behind this is that the parasites will rapidly absorb lots of water through osmosis. Water moves from areas of higher concentration to areas of lower concentration. The saltwater ich parasite is filled with salt and little water. This causes water to move into the parasite quickly and causes it to burst.
To set up a freshwater bath you add 85 percent freshwater and 15 percent water from the aquarium. The temperature and pH must be matched to that in the aquarium. Also remember to use a dechlorinator.
It is possible that your fish may go into shock. If you decide to put your fish into a freshwater bath don't leave your fish in the bath for more than 10 minutes. Remove the fish sooner if it is in distress. The fish may lay on its side while in the bath, but if it appears to really be in distress get it out immediately and place it back in the aquarium. Most fish don't last the entire 10 minutes and so be prepared for this.
To help prevent white spot and other diseases in your tank you should always use a quarantine tank before introducing new fish into an existing tank.