Fig. 22 Streptococcosis of tilapia
Pathogenic Streptococcus agalactiae or Streptococcus Dolphinus is a gram-positive cocci.
Diagnostic method (1) Field diagnosis
The sick fish swims abnormally and stops eating; Some diseased fish have exophthalmos and bleeding, one or both corneas are turbid and white, the lens and vitreous are also turbid, and even the eyeball falls off; Skin bleeding, ascites and organ diseases; In acute infection, sepsis occurs, which is characterized by extensive bleeding of internal organs, massive bleeding of liver, spleen, kidney, heart, brain, eyes and intestine; Thin bile and swollen gallbladder; The intestinal cavity is filled with yellowish liquid and the liver is swollen. (2) Laboratory diagnosis
The species of streptococcus can be determined by isolating and bacteriological identification of pathogenic bacteria in the laboratory.
Precautions (1) Strictly clean the pond with quicklime and bleaching powder. Before sowing the seedlings.
(2) Stocking healthy and high-quality fry.
(3) Maintain a reasonable stocking density.
(4) Increase the start-up time of the aerator to keep enough dissolved oxygen in the pool water.
(5) Using microbial agents and matrix improvers to improve the water quality and keep the pool water in good environmental conditions.
(6) Reduce the feeding amount, or stop feeding appropriately; Vitamin C, vitamin E, immunopotentiator such as immunopolysaccharide and enzyme can be added into the feed to improve the constitution and nonspecific immune function of fish.
(7) Correct use of chlorine-containing disinfectants to disinfect pool water and control the number of pathogens in the environment.
Treatment method (1) Stop feeding or reduce feeding first.
(2) Disinfection of pool water: disinfect the whole pool with chlorine-containing disinfectant. Mix 0.3g/m3 of chlorine dioxide with 0.3g/m3 of strong chloride, or spray 0.3g/m3 of trichloroisocyanuric acid (strong chloride) or 0.5g/m3 of sodium dichloroisocyanurate in the whole pool.
(3) On the second day after disinfection, povidone iodine (PVP-I, available iodine1%) was sprayed in the whole pond at 0.3 ~ 0.5g/m3.
(4) After stopping feeding for 4 days, resume feeding, and the feeding amount is 1/2 of the normal feeding amount (pay attention to feeding gradually according to the actual situation in the future). Before feeding, the feed and oral medicine must be evenly mixed and dried.
Oral drugs (1) were mixed with 10% florfenicol 10g or doxycycline 5 ~ 10g/kg feed, for a total of 1 week.
(2) Feed with 10% florfenicol 10g+ doxycycline 5 ~ 10g per kilogram of feed 1 week.
(3) Feed amoxicillin at a rate of 5 ~ 10g per kg of feed 1 week.
Streptococcus vaccine can stimulate fish to produce antibodies, thus mediating fish to acquire immunity. Compared with drug therapy, it is an ideal method to prevent and control fish streptococcosis with vaccine. Highly effective vaccines against Streptococcus agalactiae and Streptococcus dolphins and their extracellular protein products (ECP) have been successfully developed abroad, and patents A17,204,993 and US 6379677 (B 1) have been obtained. Streptococcus suis vaccine mainly includes whole-cell inactivated vaccine and extracellular product concentrated vaccine, which can be immunized by intraperitoneal injection and body surface immersion. 1999, the United States began to develop inactivated streptococcus dolphin vaccine, which was applied to the immune protection test of tilapia and produced good protective effect. After intraperitoneal injection of vaccine, the relative protection rate was as high as 93.2%. As for the way of vaccine administration, the protective effect of intraperitoneal injection of vaccine is far better than that of intramuscular injection and body surface immersion, and the protective force obtained by immersion of vaccine after body surface puncture is equivalent to that obtained by intraperitoneal injection. Combined vaccine is superior to monovalent vaccine. In addition, oral vaccines against Streptococcus suis are also being explored abroad. After feeding tilapia with oral streptococcus dolphin vaccine, it has obvious protective effect on streptococcosis, and the average protective rate is 63.65438 0%. At present, Schering-Plough has launched the world's first commercially produced combined vaccine of Streptococcus Dolphin and Lactococcus, which can be immunized by immersion or oral administration. Interway Company launched a monovalent inactivated vaccine against Streptococcus Dolphin in Indonesia, which was immunized by soaking or injecting. However, it has not been approved for introduction in China.
Many domestic research institutions, such as Sun Yat-sen University, Guangxi Fisheries Research Institute and Zhujiang Fisheries Research Institute, are actively developing streptococcus vaccines, but most of them are whole-cell inactivated vaccines, and the remarkable effect is injection immunization. The immune protection rate can reach more than 90%, and the immune protection of the vaccine can last for 2 ~ 3 months. However, because tilapia is easy to stab each other when injected together during immunization, the acceptance of farmers is not very high, and the operability of applying it to production practice is not strong. However, the effect of soaking or oral vaccine products is not good. Although many countries have carried out extensive exploration and research on inactivated streptococcus suis vaccine, and experiments have proved that it has achieved good immune effect. However, Streptococcus agalactiae has many serotypes and will mutate under the pressure of vaccine selection. Because the vaccine products need to apply to the management department for pilot test before entering the market, the tilapia streptococcosis vaccine has not officially entered the pilot test stage, and it will take several years for the vaccine to be developed, pilot tested and formally applied to production through approval, so the tilapia streptococcosis vaccine is still in the small-scale production test stage.