CATDOLL : CATDOLL: Why do tilapia die suddenly?

Sudden death of tilapia

1. Unreasonable breeding model

South China is a major region for tilapia farming, and it can be said that large-scale farming has been formed. At present, tilapia farmers generally adopt a three-dimensional farming model, which mainly uses livestock and poultry manure to replace part of the feed to achieve the effect of reducing farming costs. In the case of expensive labor, expensive pond rent, and expensive feed, three-dimensional farming seems to be a good way. The idea is good, but many farmers are used to discharging these livestock and poultry manure directly into the pond without treatment. The final consequence can only be that the ammonia nitrogen and nitrite in the water are too high. A large number of streptococci in livestock and poultry manure have also entered the food chain of the pond. With the continuous deterioration of the aquaculture water environment, the growth environment of tilapia is threatened. Coupled with the rising temperature year by year, it is one of the reasons for the production of streptococci in tilapia.

2. Feeding poor quality feed

Nowadays, there is a mixture of good and bad feeds, and farmers are very picky. It is understood that for poor quality feeds, the nutrition is unbalanced, and some farmers feed too much feed, which is also one of the reasons for the occurrence of streptococcus in tilapia.

3. Weather reasons

The season with a high incidence of Tilapia Streptococcus is from June to September every year, which is the best breeding stage for Tilapia when they eat a lot and grow rapidly. At the same time, during this period, there are more hot and humid weather in the south. After a long period of hot and humid weather, it suddenly rains, or there is no rain for a long time. The water quality changes greatly. Some fish ponds have poor water quality for a long time, resulting in serious excessive levels of nitrite (above 0.15mg/L) and ammonia nitrogen (above 0.8mg/L) in the water, and an imbalance of algae in the water. At this time, the fish's physique is damaged, which can easily induce Tilapia Streptococcus (and even cause hepatobiliary syndrome).

4. Choosing inferior seedlings

The most important reason for choosing inferior tilapia fry is not only that their growth rate is not uniform and they produce a lot of spawning, but also that the fry themselves are not very resistant to adversity. Especially in the hot season when fish diseases are rampant, inferior fry are more likely to get sick or even die than fry that have been hybridized and bred.

Generally speaking, the survival temperature of tilapia is between 15℃ and 37℃, and the lethal temperature is below 10℃. Most deaths of tilapia occur 2 to 3 days after the temperature drops suddenly. When the temperature rises again, the losses vary. Some are concentrated in large numbers, while others are continuously dying for several days. The sick fish were examined. In appearance, the fish body color was dull and less shiny, and the body was thin; the eyeballs were protruding, and the eye lenses were cloudy and white; the abdomen was swollen, and the epidermis was congested, but the fins and gills had no abnormal symptoms, and there were no parasites on the body surface. The anatomical examination showed that the fish abdomen was filled with water, the liver had lesions, mostly yellow and light yellow, and there were swellings and fat blocks. The above symptoms all appeared in the sick fish examined, but the manifestations were slightly different due to the different severity of the disease. Therefore, excluding parasites and viral diseases, it can be preliminarily determined that the fish are suffering from the same bacterial disease or nutritional disease. Why do tilapia die in large areas under the temperature and climate conditions, and most of the deaths occur after the temperature changes from cold to hot? Foreign data confirm that changes in environmental factors such as water temperature, salinity, dissolved oxygen, etc. have more or less adverse effects on farmed fish. In addition, other relevant data also show that when the feed lacks vitamins A, E, B_1, B_2 and zinc, fish diseases are easily induced, and the symptoms are basically similar to the above symptoms, which can be determined to be caused by nutritional deficiency. We should note that in addition to the lethal temperature, there is also the survival temperature that affects the growth of fish. At the lower limit of the survival temperature, although the fish will not die immediately, the tilapia moves slowly and basically stops eating. Therefore, during the period of sudden temperature drop, the accumulation of vitamins and trace elements in fish bodies decreases rapidly. When the weather warms up, the life activities of tilapia become more active, but due to insufficient nutrients in the body, they cannot meet the needs of life activities. At this time, pathogenic bacteria also become more active as the temperature rises. Tilapia suffers liver and kidney damage due to malnutrition, and the fish's immunity and disease resistance decrease, and then it is infected with pathogens, causing the fish to become sick and die. Therefore, the reduction of the accumulation of nutrients, especially vitamins and inorganic salts in the fish body, is an important cause of tilapia death.

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