A Detailed Guide to Common Grouper Diseases and Their Prevention and Treatment Methods

Grouper is a relatively popular fish nowadays, and with the hype of recent years, its market price has shown a trend of only rising, never falling. Although grouper is a marine fish, it can also be farmed using freshwater aquaculture methods, so more and more people are now farming grouper in freshwater. However, farming grouper is not a simple matter, as grouper is prone to many diseases. So what diseases can grouper develop? How should they be prevented and treated? Let's take a look!

1. White spot disease (white patch disease)

Disease characteristics: White patch disease is one of the most harmful diseases to grouper, generally occurring in high-density and cage-culture environments. White patch disease develops quickly and is extremely contagious; in severe cases, it can cause large-scale grouper deaths within no more than 5 days. White patch disease is mainly caused by parasites, and white patches appear on the skin, fins and gills of the grouper. The patches gradually expand, and eventually all the patches merge together. Mucus at the gills increases, the grouper cannot breathe, and after onset, diseased fish can often be seen floating on the water surface.

Prevention and treatment methods: Once white patch disease is confirmed, place the diseased fish in clean freshwater for about 5 minutes, which can eliminate a certain amount of the pathogens. This is for marine aquaculture; for freshwater aquaculture, bleaching powder or potassium permanganate solution can be used to wash the diseased fish.

2. Viral nervous necrosis

Disease characteristics: Necrosis generally occurs in fry at 3-4 weeks of age. After the fry are infected, there are initially no particular signs, but their appetite gradually declines and they do not swim along with the school. However, as the disease spreads, the diseased fish become like a “land duck”, unable to swim normally, with their bellies appearing very large as if they have overeaten. They often lie on their backs on the water surface, which is what rural people call “turning white”. When the diseased fish are taken out, their heads are found to be red and swollen, their abdomens are distended, and their swim bladders become larger than usual, congested and swollen. They generally die within about a week.

Prevention and treatment methods: Necrosis is mainly dealt with through prevention. When purchasing fry, the seed stock must be carefully inspected; avoid selecting those carrying pathogens or diseased stock, which should be burned immediately. Once diseased fish are found, they should be taken out promptly and reared separately from other fish, and bleaching powder should be used to disinfect the pond. When temperatures are high, reduce the farming density, ensure high-quality bait and water quality, improve the nutritional value of the bait, and enhance the disease resistance of the fish.

3. White spot disease (ich)

Disease characteristics: No matter what kind of fish it is, the chance of parasitic diseases occurring is the highest, and among them, the threat of white spot disease (ich) is relatively great. When diseased fish contract ich, white spots of various sizes appear on the surface of the fish body. As the disease progresses, more and more mucus appears on the fish body surface, the scales begin to fall off, and swimming is also restricted. The incidence rate is generally highest in high-temperature pond-culture environments.

Prevention and treatment methods: Before stocking the fish, the pond must be thoroughly disinfected, and the farming density of the pond must be well controlled so as not to exceed the pond's carrying capacity. After the disease is found, the diseased fish should be isolated promptly and soaked in a mixed solution of glacial acetic acid and hydrogen peroxide for about one hour. In addition, all unaffected fish in the pond should be soaked in formalin for about 60 minutes, roughly once every 3-5d.

The above is a brief introduction to the common diseases of farmed grouper and their prevention and treatment methods. Of course, there are more than these, such as whirling disease and dactylogyrus disease. Most of these are parasitic diseases, so prevention work still needs to be done well. The onset and spread of parasitic diseases are much faster than those of traditional diseases, so do a good job in daily management, reduce parasites, and lower the incidence rate. This article is for reference only and is hoped to be of help to everyone.