How to Diagnose Sick Saltwater Fish

You can diagnose a sick saltwater fish by observing its behavior and physical symptoms. When you̵7;re attempting to diagnose the fish̵7;s illness, the disease will fall into one of four categories: bacterial infections (̶0;fin rot,̶1; fish tuberculosis and vibriosis), viral infections (lymphocystis), fungal diseases (Ichthyophonus or ̶0;Ich̶1; and exophiala), or parasitic infestations (marine velvet and white spot). The most important time to watch out for saltwater fish diseases is when you first purchase a fish.

Things You'll Need

  • Appropriate medications
  • Quarantine tank (optional)
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Instructions

    • 1

      Diagnose marine velvet in your saltwater fish by looking for a dusty, white or gold ̶0;film̶1; on the fish̵7;s body, respiration problems, paleness and constant scraping against rocks or tank substrate. Marine velvet is caused by tiny parasites that feed on the fish̵7;s tissues. It is treated with an anti-parasitic medication for two weeks.

    • 2

      Diagnose a viral infection by studying your sick saltwater fish for hard warts on its body, around its mouth and on the edges of its fins. These symptoms indicate lymphocystis, which is not usually fatal and can cure itself in two or three months, although you̵7;ll still need to quarantine the infected fish.

    • 3

      Look for symptoms such as fuzzy gray or white areas on the fish̵7;s body or mouth to diagnose a fungal infection. Fungal infections usually occur only when the fish̵7;s immune system is impaired, often following or in conjunction with an injury or parasitic infection. Treat the fish with methylene blue, malachite green or an appropriate fungicidal medicine.

    • 4

      Watch for bulging eyes, severe weight loss and red swellings or other changes in body color to diagnose an internal bacterial infection. Internal bacterial infections, usually fish tuberculosis or ̶0;wasting disease,̶1; most often occur in overcrowded tanks and older fish.

    • 5

      Determine whether your saltwater fish has an external bacterial infection by inspecting your fish for rotting fins or tails with red or brown discoloration, open wounds and spreading body ulcers. Both external and internal bacterial infections can be fatal and must be treated with the appropriate antibiotics.

    • 6

      Diagnose white spot disease by looking for symptoms such as thick body-slime buildup, more rapid respiration and large white spots appearing on the fish̵7;s body. Like marine velvet, white spot disease is a parasitic infection, but the treatment course is longer̵2;about three weeks.