Crab-like foam disease in tilapia

The "crab foam" phenomenon: Parasitic spores infect the gills of fish, causing them to swell and become damaged, making it difficult for the fish to breathe. The fish then has to surface to get oxygen; at that time, air bubbles appear, resembling crab foam, hence the name "crab foam" disease.

Reason

- Caused by parasitic spores. This is the first factor that weakens the fish, leading to attacks from other agents (such as bacteria, fungi, and parasites).

- The old pond was not properly renovated or treated.

- The fish fry carried pathogens; the fish fry were not quarantined.

- The disease spreads from one pond to another.

Symptom

- Fish secrete a lot of mucus, their color is paler or darker than normal (black body). The gills are pale and float to the surface of the water. Fish often congregate at the entrance of the drain, swim erratically, and have slow reflexes.

- After a few days, the fish started dying in small numbers, then the number of deaths increased very rapidly.

- The "crab foam" phenomenon: Parasitic spores infect the gills of fish, causing them to swell and become damaged, making it difficult for the fish to breathe. The fish then has to surface to get oxygen; at that time, air bubbles appear, resembling crab foam, hence the name "crab foam" disease.

Because both the cysts and spores of the parasite have a hard chitinous shell, and because the cysts live at the bottom of the pond, using chemicals to kill them requires much higher concentrations than other pathogens. However, if chemicals are used in a pond already containing fish, the fish will die before the pathogens are eliminated. Therefore, essentially, crab foam disease can only be prevented, not cured.

Ways to prevent the disease

- Clean the pond thoroughly before each farming season, making sure to dry the pond bottom for over 10 days and treat the water before stocking.

- Select good quality, disease-free, and quarantined broodstock. Bathe the broodstock in a 2-3% salt solution (200-300g/10 liters of water) for 5-10 minutes before releasing them.

- Maintain an appropriate stocking density; polyculture is recommended to help manage and stabilize the water environment more effectively.

- Feed and care for the farmed fish using proper techniques.

- Maintain good pond water quality throughout the farming process, minimizing water changes to stabilize the farming environment.

- Regularly treat the water and pond bottom with biological products or zeolite.

- It is possible to raise the fish in two stages to facilitate pond bottom cleaning and separate the fish by size. Note: when transferring fish to another pond, fast them for 1-2 days beforehand; the process must be quick, gentle, and done when the weather is cool.

- Dissolve lime and coarse salt in water and spread it into the pond, at a dosage of 1-3 kg/100m³ of water. Use some medicinal herbs (such as *Gynostemma pentaphyllum* leaves, *Acacia mangium* leaves, etc.) soaked in the pond water.

If fish die during the rearing process, they must be removed and buried or burned to prevent the spread of disease; at the same time, the pond water must be treated and not discharged directly into canals or ditches. If the fish reach marketable size, they must be sold immediately. If rearing continues, improve water quality (change water, disinfect) and increase the fish's resistance (mix Vitamin C into the feed) to help them stay healthy and overcome disease. However, this method only saves healthy fish, as there is currently no cure for the protozoan parasite; the main focus is on disease prevention throughout the rearing process, especially pond and water environment treatment.

According to thuysanvietnam - LY