Symptoms and Prevention of Infectious Pancreatic Necrosis in Salmonids

Pathogen: The pathogen is infectious pancreatic necrosis virus.

Transmission routes: vertical transmission: eggs and milt of virus-carrying broodfish; horizontal transmission: feces, urine and secretions of diseased fish carry the virus into the water, and the routes of infection are the gills and mouth.

Symptoms: juvenile fish weighing more than 5 grams are mostly chronic cases, with slower death; externally, the abdomen is distended, the body color darkens, the eyeballs protrude, the fin bases and abdomen are congested and red, the anus mostly trails string-like feces, swimming is slow, and feeding is poor. Fry weighing less than 5 grams are mostly acute cases, with rapid death; diseased fish move sluggishly, swim on their sides or slowly rotate and then sink to the bottom, with a distended abdomen and darkened body color.

Epidemiology and harm: This disease mainly affects the fry and juvenile fish of salmonid fishes. Seed stock at 2 months after first feeding often suffers acute mass mortality; death generally begins 7 weeks after first feeding, larger fry are affected first, and juvenile fish over 20 weeks of age generally no longer develop the disease. The disease occurs at water temperatures of 10°C to 15°C; at water temperatures of 10°C to 12°C, the mortality rate can reach 80% to 100%. The incubation period of the disease is related to fish size and water temperature: the larger the fish, the longer the incubation period; the higher the water temperature, the shorter the incubation period.

Prevention: Do not use pathogen-carrying broodfish to breed young; do not transport fish and eggs from disease-affected areas; use independent water bodies for spawning, fry hatching and rearing; fry and fingerlings should be placed at the most upstream part of the fish farm to prevent horizontal transmission; prevent water source contamination; diseased and dead fish should be destroyed promptly; thoroughly disinfect aquaculture facilities and tools with high-concentration chlorine preparations; disinfect fish eggs with povidone-iodine at 50 mg/L for 15 minutes.

Treatment: In affected ponds, the development of the disease is generally controlled by raising the water temperature.