Generally, 0.3-0.5% salt is enough. Adding salt can reduce the chance of fish getting sick, especially during illness, which can keep the fish stable.
Common diseases of grass carp include bacterial gill rot, bacterial enteritis and erythroderma. All kinds of grass carp will get sick, and the economic losses caused by it also rank first among grass carp diseases. In order to effectively prevent and control these three diseases. Details are as follows:
1. Pathogens: Cellulophila cylindrica, Aeromonas punctata and Pseudomonas fluorescens.
2. Epidemic law: the epidemic season is from April to 65438+10, with two peaks. It mainly harms 1-2-year-old grass carp from April to June, and harms grass carp fingerlings in that year from August to June. Generally, it becomes popular when the water temperature is above 18℃, with the peak at 25℃-30℃. It is rich in pond water and sediment. When the water quality and fish health are good, dominant populations cannot be formed, which will infect fish and cause fish diseases. When feeding a large number of inferior bait, water quality deterioration or other reasons lead to the decline of fish resistance, they multiply and invade fish, thus causing diseases. Pathogens can be discharged into the water with the feces or carcasses of sick fish, polluting the bait and infecting other fish through the mouth, thus forming a large-scale outbreak of grass carp "three diseases".
Third, the main symptoms: the sick fish can't swim alone, the head is black, and the gill cover has translucent holes. In severe cases, gill cover is rotten and worn, gill filaments are swollen, congested and inflamed, rotten and silted, abdomen is congested and red, and scales fall off loosely. The anus is red and swollen, and yellow mucus flows out when the abdomen is lightly pressed. Anatomy showed that there was no food in the intestine, the intestinal wall was purple with congestion and inflammation, and the liver was yellow.
4. Etiological analysis: The first peak of grass carp's "three diseases" appeared in April-June, just at the turn of spring and summer, and the daytime temperature was higher than the water temperature. With the increase of temperature, the surface water temperature gradually increases and the density gradually decreases. The temperature is lower than the water temperature at night. With the temperature gradually decreasing, the surface water temperature gradually decreases and the density gradually increases, resulting in the density of the surface water body being higher than that of the bottom water body, thus causing convection between the upper and lower water bodies. A large number of pathogenic bacteria in sediment are brought into the whole water body, which increases the chances of contact between cultured fish and pathogenic bacteria and eventually leads to fish diseases. The second peak of grass carp's "three diseases" appeared in August -65438+ 10, which is the turn of summer and autumn. The change of water temperature and air temperature is the same as that at the turn of spring and summer, so it will also cause water convection and fish diseases. In addition, after several months of cultivation, a large number of residues, bait, dead organisms and fish residues have accumulated at the bottom of the pond, and the water quality has also deteriorated seriously, which is also easy to cause a large number of pathogenic bacteria in the water to multiply, eventually leading to fish diseases.
Five, prevention and control measures: do a good job in pond sanitation, maintain a good breeding environment, for the improvement of pond environmental conditions, especially the bottom material, you can also take the method of applying quicklime in the pond. Quicklime can not only loosen the sludge, improve the ventilation condition at the bottom of the pond, accelerate the decomposition of organic matter, reduce the generation and accumulation of ammonia nitrogen and nitrite, but also kill pathogenic bacteria and spores in the sludge, and achieve good disease prevention effect. Common methods include cleaning the pond with quicklime (50- 100 kg/mu) and sprinkling quicklime (15-20 kg/mu? M, 1-2 times/month). In the process of aquaculture management, we should always implement the principle of "prevention first, combination of prevention and control, prevention before illness and early treatment of illness", and prevent and control fish diseases throughout the whole aquaculture cycle to avoid causing greater economic losses.