Saltwater Fish: Diseases and Fungus

Saltwater fish are prone to several diseases and fungal conditions---particularly when kept in aquarium tanks. Close proximity to other fish can also mean that infections spread unless treated. The most common infections in saltwater species are parasitic in nature, though there are some viral and fungal conditions to watch out for. Some of the most common saltwater fish diseases include marine ich, marine velvet, Ichthyosporidium and head and lateral line erosion.

  1. Prevention

    • Saltwater fish kept in aquariums are more vulnerable to infection when stressed or undernourished, according to the University of Florida. Tanks should be large enough to accommodate fish, with plenty of room to swim freely. Appropriate food needs to be provided, with the right levels of protein or vegetable matter. Salt content, pH and temperature of the water should also be closely monitored. Different species require different water conditions. Adding aquatic plants can give fish a place to shelter and improve the oxygen content of the tank.

    Marine Ich/White Spot

    • Marine ich or white spot disease is one of the most common conditions to affect saltwater fish. It can occur in nearly all saltwater species, except for rays and sharks, according to the website "Aquarium Community." The name "white spot" is derived from the small light spots that appear on the skin, gills and fins of infected fish. Each spot is a small protozoan parasite growing on the fish. If untreated, marine ich can be fatal. Treatments include specially medicated food, available from pet or aquarium stores.

    Marine Velvet

    • Marine velvet gets its name because it creates a velvetlike film across the skin of an infected fish. It's also known as rust or gold dust disease. It is a fast-acting and contagious infection. Treatment should occur soon after symptoms are seen. Aside from the velvet coating, other signs may include fish rubbing up against tank walls and rocks, and fast-breathing motions at the gills. Copper medications from aquarium specialist stores can be used to treat fish affected by marine velvet. Copper medications are liquids mixed directly with aquarium water in concentrations that can control the spread of marine velvet and ich. Care should be taken not to exceed recommended dosage, as copper can poison saltwater fish.

    Fungal Infections

    • Fungal infections in saltwater fish are usually accompanied by bacterial or parasitic conditions. Healthy fish are far less likely to become infected by a fungus. Ichthyosporidium is one fungus that attacks weakened saltwater fish. It is a potentially very damaging infection that spreads internally. Symptoms include a hanging, hollow belly and erratic lopsided swimming. Treatments such as malachite green can often combat simple fungus outbreaks. Malachite green is a liquid medical treatment for parasite, protozoa and fungal fish infections and is available at many aquarium and pet stores.

    Marine Head and Lateral Line Erosion (HLLE)

    • Head and lateral line disease or erosion is a condition that can cause dents, holes and sores on the body. The condition is sometimes referred to as hole in the head disease because of the holes that can appear around the face and head. Lesions and marks can also appear along the central (lateral) line of the fish. Exact causes are unknown. Keeping water clean, well-filtered and oxygenated can help prevent the disease.