RECOGNIZING DISEASE IN FISH

The most important job of a producer is to manage disease. Early diagnosis and treatment is paramount to high survival rates and effective management. Recognizing early signs of disease in fish can be difficult in certain infections. Depending on the disease, you may see physical or behavioral signs, and being able to pick them out early in an infection is the most important aspect of good fish health.

Physical signs of sick fish are relatively easy to spot. This includes spots, tears, growths, color change or missing parts. A wide range of diseases can affect a fish's outward appearance. Many of the diseases commonly found in aquaculture are secondary to stress, and no stressor is more common than water quality. Water quality is the most important aspect of fish health. Like the air we breathe, the water a fish swims in is paramount to its health and longevity. At the start of any disease outbreak or suspicion, water samples should be tested immediately before any other action other than quarantine is taken.

Spots on fish can present in a wide array of colors and appearances. Some spots can be disease specific, such as "White Spot Disease," also known as Ich, short for the parasite, Ichthyophthirius multifiliis. Green spots on fish, usually caused by opportunistic algae growth, indicate a loss of immunity at a spot in the skin. This is caused by trauma to a small piece of skin or scale that is dead but remains on the fish. Red spots usually indicate the start of an ulcer or bruise. Ulcers are very serious since they interfere with the protective barrier of the outer skin, allowing more bacteria and parasites to enter the fish. Bruises can be secondary to flashing, a behavior cause by skin ectoparasites. Other spots are usually dependent on the species and species-specific diseases.

Behavioral signs of disease can include body posture, buoyancy, swimming or appetite. Body posture involves how the fish holds itself in the water. A healthy fish is parallel to the surface of the water and symmetrical bilaterally. Sick fish may list to one side or have their head or tail elevated. Buoyancy is where a fish sits in the water column. Both positive and negative buoyancy disorders are common in fish. Swimming may be erratic and disoriented. A fish's appetite is a good measure of its overall health. A fish that does not want to eat is a positive indicator that disease is present.

Many factors go into monitoring fish for good health. Knowing your fishes' normal behavior is important in determining when disease is present. Catching disease early and treating appropriately is very important to good fish health and yields.