Whether you have a fish aquarium or reef tank, saltwater fish provide constant entertainment with their interesting personalities, behavior and beautiful coloration. Despite the best of care, marine fish can become sick when aquarium conditions stress fish and favor disease-causing organisms. Common saltwater fish diseases are present in every aquarium. If youâ€™ve been reading our TB Aquatics blog posts you know how much we emphasize keeping the aquarium water clean in order to reduce stress on corals and other invertebrates. The same advice goes for reducing saltwater fish diseases in your marine fish aquarium and reef tank. Poor water quality creates conditions that increase fish stress and promote the proliferation of disease-causing organisms in your marine aquarium. Many disease-causing organisms thrive in dirty, organic-rich saltwater tanks. Likewise, fish rarely get sick in well-kept, cleanÂ aquariums. This article will highlight the most common saltwater fish diseases and how to avoid them.
Bacterial diseases of saltwater fish
Bacterial diseases of marine fish have similar symptoms
It is important to understand that in most cases of bacterial infections we can only visually identify generalized symptoms and not the actual bacterial strain that is causing the illness. Specialized diagnostic testing is required to isolate the specific bacteria. These tests require tissue samples of skin, fins, gills and internal organs. Aquarists can only rely on visual symptoms since these invasive tests would kill the fish. Many of the common bacteria pathogens cause the same outward symptoms. These include fin and tail rot, ulcers and open sores, loss of color, loss of appetite, low energy and heavy breathing. Bacterial infections occur when a fish is stressed and has a weak immune system. Fin and skin damage can open up tissue for attack by bacterial infections. Some infections can be treatable if discovered early. In some cases the bacterial infection is internal and has no outward signs. The fish can behave normally, eat well and have normal coloration and suddenly die for no reason. A dissection almost always reveals internal organ damage from bacteria.
Treating bacterial infections in saltwater fish
Ideally youâ€™ll notice the symptoms of bacterial infection before it progresses too far. If possible, place the fish in a recovery aquarium during treatment. This will isolate the fish from its tank-mates and make it easier to dose with medications. Bath treatments with antibacterial medications can help if the bacteria strain is susceptible to the medication. If your fish is hiding in a reef aquarium the choices for treatment are limited. Many reef aquarists do not want to risk harming their corals while treating the entire aquarium with chemical treatments. Some natural botanical antibacterial medications wonâ€™t harm invertebrates but cause heavy, wet foaming in protein skimmers. This is due to a natural emulsifying ingredient that makes the botanical oil water-soluble. It can take several weeks for the emulsifier to break down in the aquarium and the foaming to dissipate. Medicated fish foods are modeled after commercial aquaculture practices. The idea is to put the medication directly inside the fish, not the aquarium water. If your fish will eat the food it may be the best option when treating bacterial fish diseases in marine and reef aquariums. Antibacterial medications are available for treating fish-only and quarantine aquariums.
Viral infections of marine fish
Lymphocystis is a common viral disease in marine fish
Marine fish are subject to iridovirus infections. Â Viruses are small infectious particles that replicate themselves inside the fishâ€™s cells. The virus particles contain genetic DNA covered by a protective layer of protein. A typical virus is a hundred times smaller than the average bacterial cell and canâ€™t be seen through a regular microscope. Angelfish, butterflyfish and clownfish are susceptible to Lymphocystis. This common saltwater fish disease looks like tiny grape-like clusters of virus-laden cells. The clusters often appear light in color. Fortunately Lymphocystis is non-life threatening and usually clears up over time. Megalocytiviruses have also been found to infect tropical marine fish. Symptoms include loss of appetite, darkening, abnormal swimming (including spinning), heavy breathing, bloating, ulcers, and death. Internal organs can be enlarged or partially dissolved.Â Viruses spread through direct contact, water, eating an infected fish, or even in feces.
Treating marine fish viruses
There are no anti-viral treatments for marine aquarium fish. The good news is that proper care and feeding will keep the fishâ€™s immune system in top shape and prevent viral infections. Prevention through good aquarium maintenance is the best defense against viral outbreaks. This includes testing the water, protein skimming and water changes.
Fungal infections of saltwater fish
Ichthyophonus hoferi is a parasitic fungus that attacks marine fish. The fungus can enter the fish through open wounds, eating other sick fish or through damaged gills. The fungus causes damage to internal organs including the swim bladder, brain, spleen and liver. There are no outward symptoms in the early stages of the disease. In more advanced cases the fishâ€™s skin can appear rough and bumpy. Fusarium solani is a fungal disease associated with low water temperature. Angelfish and parrot fish appear to be the two most susceptible types of marine fish to Fusarium. Advanced symptoms include internal muscle and organ damage and bloating.
Treatment of saltwatermarine fungal infections
There are no medications for treating marine fungal diseases in marine fish. The best approach is prevention based on maintaining a stable water temperature, proper water chemistry and good diet. Keeping the aquarium clean and free of debris can also help reduce the chances of infection.
Parasitic infestations in marine fish
Saltwater ich is caused by an external ciliated parasite
There are several common parasites that infest saltwater fish.Â Ciliated protozoan parasites are the most common external parasite. Ciliates can swim in the aquarium water, attach to the fishâ€™s fins and skin, or burrow just under the skin. Saltwater ich (Cryptocaryon irritans, one of the most common saltwater fish diseases, infests the fins, skin and gills of marine fish. The parasites can weaken the fish, suffocate the fish through gill damage and even create tiny wounds that invite bacterial infections. Fish develop distinct white spots accompanied by scratching and heavy breathing.
Brooklynella is another ciliate parasite that infests marine fish. The parasite is microscopic and cannot be seen with with the eye. Infested fish suffer from heavy breathing, coughing and scratching. The parasites irritate the skin, causing patchy slime on the skin. Clownfish appear to be very susceptible to Brooklynella parasites.
Brooklynella on a clownfish
Parasitic worms are also attack marine fish. Benedenia and Neobenedinia infest the skin and eyes of saltwater fish. Sick fish will lose weight and scratch. Open lesions can form due to tissue damage and secondary bacterial infections. Infested fish may sit on the bottom of the tank or hang near the water surface.
Trichodina are disc-shaped ciliated parasites. The parasites move around the surface of the fish, feeding on skin cells and fluids. This irritation causes the fish to dart and scratch. Trichodina infestations weaken the fish, allowing for other diseases to take advantage of the fish.
Treatment of marine parasites in saltwater fish
Identifying saltwater fish parasites requires a microscope and diagnostics skills. Hobbyists can only see symptoms of the disease in most cases. Common saltwater fish diseases, including parasites, can be spread from fish to fish and tank to tank through water, nets and even wet hands. Fish-only tanks can make use of over-the-counter anti-parasitic treatments like copper, formalin and malachite green. Anti-worm treatments containing praziquantel have successfully treated worms in marine fish. Â The safety of anti-parasitic treatments in reef aquariums remains questionable. Most reef aquarists choose to not to add common saltwater fish disease medications to their reef because corals and other invertebrates are sensitive to chemical treatments. The good news is that if the water quality is maintained, marine fish in reef tanks will often recover without medication.