How to prevent and treat vibriosis in rainbow trout farming? A detailed practical guide

1. Symptoms: Diseased fish feed poorly, the body color darkens, the bases of all fins become congested, the body surface, oral cavity and anus become red and hemorrhagic, and the gill filaments are anemic and slightly pale. Some fish have protruding eyeballs. Larger fish or adult fish often show signs on the body surface such as erosion, rupture, whitening, dermal ulceration and muscle necrosis, and hemorrhagic spots can sometimes be seen everywhere.

2. Pathogen: Vibrio anguillarum. Gram-negative, short rod-shaped, cells straight or slightly curved, with rounded ends, single or in pairs, without a capsule, non-acid-fast, usually with a single polar flagellum, motile. Hemolytic, ferments glucose to produce acid but not gas, sensitive to streptomycin, novobiocin, oxytetracycline, chlortetracycline and the vibriostatic agent (0/129), and produces toxins. Growth temperature 5-43°C, optimum temperature 18-37°C, growth pH 5.8-10.5, can grow in 0%-5% sodium chloride, but grows poorly in medium without sodium chloride, and does not grow in 6% sodium chloride. 3. Epidemiology: Vibriosis of rainbow trout is a disease of worldwide prevalence. Rainbow trout from several months after hatching to about 1 year old are susceptible, the disease course develops quickly, and mortality is high. Larger rainbow trout and even broodstock can also be infected, but it is mostly chronic. This disease begins to occur when the water temperature is above 18°C, and deaths slowly stop only after the water temperature drops below 18°C in late autumn, ultimately causing serious losses. 4. Prevention and treatment methods (1) Vaccination with Vibrio anguillarum vaccine, generally using a formalin-inactivated vaccine. Vaccine inoculation methods include:

Intraperitoneal injection: the best effect, and it produces the fastest immune effect, and the vaccine dose required is also the smallest, but it is too troublesome and easily injures the fish. The fish can first be anesthetized with ethyl aminobenzoate, then each fish is injected with 0.1 milliliter of inactivated vaccine. Immersion method: this method is relatively commonly used; immersion at 10000000 bacteria/milliliter for 5 minutes, or immersion at 10000 bacteria/milliliter for 3-6 hours, is effective; immersion in 0.94 grams (wet weight) of vaccine/liter and 5.32% sodium chloride hypertonic solution for 3 minutes is also effective. The immune period is 113 days. Spray method: at 7 kilograms pressure per 1 cubic centimeter, at a distance of 15 centimeters, spray for 5-10 seconds, with each gram of carrier containing 0.01 milligram wet weight of vaccine. Oral method: feed 4 grams of wet vaccine per kilogram of fish per day, continuously for 30 days, which is effective. The disadvantage of this method is that the vaccine dose required is large, and it must be fed continuously many times. (2) Feed 2-5 grams of doxycycline per 100 kilograms of fish per day mixed with bait, once a day. Feed continuously for 6 days. (3) Feed 5 grams of oxytetracycline per 100 kilograms of fish per day mixed with bait, once a day, for 3-7 consecutive days. The above oral therapeutic drugs should be used in combination with spraying 0.3 milligram/liter of strong chlorine powder over the whole pond to disinfect the pond water and the fish body.