First, high temperature, water quality deterioration, high culture density, high organic matter concentration, germplasm degradation, unscientific feed feeding, drug abuse and other factors lead to low disease resistance of fish, which in turn makes fish infected with streptococcus and sick. It should be pointed out that Streptococcus tilapia is an opportunistic pathogen, not all tilapia infected with Streptococcus tilapia will get sick, and only if it meets the pathogenic conditions will it get sick.
Two factor analysis 1. The concentration of organic matter in the pond is high: the stocking density of fish is high, exceeding 3000 fish/mu, and it consumes and excretes more; Under the condition of three-dimensional culture of fish and pigs in Yangjiang area, pig excrement directly enters the pool; When the temperature is higher than 32℃ (Guo Enyan et al., 20 1 1), the food conversion rate of tilapia is obviously reduced and the excretion is increased.
2. Poor water quality: too much organic matter, insufficient oxygen conditions, and poor nitrogen circulation in the pond, resulting in excessive nitrogen (ammonia nitrogen+nitrite) concentration;
3. Deterioration of bottom mud: there are many organic matters and insufficient oxygen in the bottom of the pond, and anaerobic bacteria or facultative anaerobic bacteria at the bottom of the pond multiply and grow rapidly;
4. Rapid propagation of Streptococcus tilapia: the pathogen is facultative anaerobic bacteria, which grows and propagates rapidly when the water temperature exceeds 32℃;
5. Weak fish: The bad water environment, such as high nitrogen concentration, low dissolved oxygen at the bottom of the pond and water temperature higher than 32℃, exceeds the suitable growth range of tilapia, making the fish weak.
Suggestions on preventive measures for streptococcus: 1. Quality control of organic matter: the density should be reduced to below 1500/ mu; Adjust the ratio of pond area to pig stock to reduce the amount of pig manure discharged into unit farming area; When the water temperature exceeds 32℃, control the material;
2. Water transfer: Turn on all aerators at the right time. When the water temperature is not the highest and the dissolved oxygen in the upper layer is rich, such as 10:00~ 12:00, the purpose is to break the water layer and repay the oxygen debt at the bottom of the pool in advance. It is more appropriate to control the transparency at 30cm; If the transparency is too low, photosynthetic elements will be refreshed; If the transparency is too high, Shen Shuang EM 10+ amino acid fertilizer paste;
3. Bottom modification: Shenshuangshuang bottom/potassium persulfate or hydrogen peroxide/granular oxygen, and the bottom modification time is set according to the feeding amount and pig manure discharge amount;
4, enhance physical fitness: oral mixed ingredients at intervals, Shenshuangyubaokang/Shenshuangyiluxiang/Gao Zhen/Immunopolysaccharide, single product or mixed ingredients can be used; Use Luo Fei Zhuang's materials.