Saltwater aquarium fish

Wed Jan 14 14:58:28 UTC 2015

In this article we will take a look at three of the most commonly occurring diseases in marine aquariums: marine ich, marine velvet, and black spot disease. As with most parasitic diseases, you can decrease the risk of outbreaks by utilizing a quarantine aquarium and keeping your fish in optimal conditions. A suitable diet will also boost resistance against parasites and other health problems.

Marine Ich

Marine ich is one of the most common diseases in marine aquariums. The symptoms of marine ich, also known as marine ick and marine white spot disease, are very similar to the symptoms of freshwater ich, including white spots and scratching. The two diseases are however caused by two different parasites; Ichthyophthirius multifiliis causes ich in freshwater aquariums while Cryptocaryon irritans is the culprit in saltwater tanks. Marine ich can infest almost all species of saltwater fish but some fish groups, such as surgeonfish, are more susceptible than others. A fish that survives marine ich may develop immunity for up to six months.



The life cycle of Cryptocaryon irritans is very similar to that of Ichthyophthirius multifiliis and this must be taken into account when treating the disease. Never stop treatment prematurely just because you can’t see any symptoms of disease.

Keeping your fish in good condition will make them less susceptible to marine ich, and installing an ozone filter can also be helpful.

Just as with the freshwater variety, many different marine ich treatments exist. One example of an effective remedy is to lower the salinity down to 1.009-1.010 for 2-3 weeks, and then slowly increase the salinity back to its normal level. Most invertebrates and some fish species will not tolerate this treatment.

Another marine ich remedy is adding 0.15-0.25 mg copper per litre water. You must however first research how sensitive the inhabitants of your aquarium are; some species will not even tolerate 0.15 mg/ L. Also keep in mind that calcareous media such as coral sand and live rock will absorb copper.

A third method is to combine medicated food (e.g. metronidazole) with cleaner shrimp. Cleaner shrimp can also be used to prevent marine ich.

Marine velvet

Marine velvet is caused by a parasite named Amyloodinium ocellatum. Its lifecycle is similar to that of the parasites that causes marine and freshwater ich and to the species of the genus Piscinoodinium that causes freshwater velvet. An infested fish that survives the attack may develop immunity for up to six months.

Amyloodinium ocellatum will typically attach itself to the gills of the fish but can infest the skin as well and cause a characteristic velvety sheen. One way of diagnosing the disease is to turn of the lights in the aquarium and in the rest of the room and light up the top of the fish using a flashlight. In a fish infested with marine velvet, gills and/or sides will usually look velvet or gold dusted under indirect light.

Marine velvet can be treated with the same copper treatment used for marine ich (see above). Another method is to administer a single dose of 5-10 mg chloroquine diphosphate per litre of water. Chloroquine diphosphate is toxic to micro algae, macro algae and many invertebrates.

Five minute freshwater dips will usually kill the parasites on the fish, but there is a high risk of re-infestation as soon as you return the fish to the infested aquarium.

Marine black spot disease

Marine black spot disease is also known as black ich and tang disease. Tang and surgeonfish are especially susceptible to this disease but it can affect a long row of other fish species as well. The culprits are turbellarian flatworms belonging to the genus Paravortex.

The life cycle of Paravortex flatworms somewhat resembles that of marine ich parasites. The young Paravortex organism lives in the substrate until it matures into an adult worm. The adult worm seeks out a suitable host fish and commences feeding. After roughly six days of feeding, the flatworm will fall down to the substrate again. About five days later, its body will rupture and a new batch of young ones is released. The cycle will now start over again.

When a Paravortex flatworm starts feeding it develops pigmentation and this is why infested fish becomes covered in black spots. The spots can look similar to grains of salt, but are black in colour. Other symptoms of marine black spot disease are scratching, anorexia, lethargy, rapid breathing, and loss of colouration. Secondary bacterial infections can occur in damaged areas.

Marine black spot disease can be treated by first giving your fish a freshwater dip and then following it up by a formalin bath. The freshwater dip should ideally last for 3-4 minutes, but you should remove the fish earlier if it shows signs of serious stress. For the formalin bath it is important to follow the recommendations from the manufacturer of the formalin product since different products have different strengths.

Dipping and bathing your fish will not remove the parasites from the aquarium and the risk for re-infestation is therefore high when fish are returned to their old home. Ideally set up a new aquarium and leave the infested one without fish for several months. If this is not possible, you can try using hyposalinity to kill the parasites. The salinity must be lowered to 12-14? (this is equivalent to a specific gravity of 1.009 at a water temperature of 79-82°F). Unfortunately, quite a few marine aquarium species won’t survive such a low salinity.

Source: AC marine aquarium.