Question of the Week
Answer: Tilapia have historically been considered a very disease-resistant, or resilient, species. However, researchers and practitioners are beginning to dispel this notion, as there are some diseases that occur in tilapia populations that can negatively impact production. One such disease is streptococcuss.
Streptococcus affects the nervous system and causes swirling behavior, lethargy, bent bodies, and disoriented fish. Other symptoms include eye lesions, abscesses, skin hemorrhages, and ascites, or the presence of abdominal fluid, often seen in association with a protruding anus.
Outbreaks happen when fish are exposed to stress, such as an increase in water temperature, suboptimal oxygen levels in the water or overcrowding for a long period of time. The disease is transmitted horizontally from fish to fish (via cannibalism, skin injuries, etc.), and also from the environment to the fish. It affects all fish sizes; however, bigger fish (from 100 grams to market size) are usually more susceptible to the disease.
If infection is thought to be present, a lab analysis should be done.
Treatments include decreasing feeding, decrease stocking density, maintaining optimal oxygen levels by aerating the water, lowering the water temperature, and using an antibiotic treatment. Antibiotics are only effective in treating a streptococcus outbreak if treatment is applied very early during the course of the disease, when fish are still feeding normally.
To learn more about aquaponics, consult the ATTRA publication Aquaponics — Integration of Hydroponics with Aquaculture
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