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Infectious hematopoietic tissue necrosis of salmon and trout

Published: 2024-11-22 Author: mysheen
Last Updated: 2024/11/22, The pathogen is infectious hematopoietic tissue necrosis virus. Vertical transmission: eggs and semen of infected parent fish are more likely to be transmitted by eggs; horizontal transmission: water source is polluted, etc. The virus mainly invades the fish through the Gill and digestive tract. Symptoms the disease often causes sudden mass death in the fry and juvenile stage, and usually occurs 7-14 days after infection. The diseased fish swims slowly, rotates, sometimes sinks to the bottom, the body color turns black, the abdomen is dilated, the fin base is congested, the anus hangs opaque, mucous feces, and the lateral muscles are "V" shaped.

The pathogen is infectious hematopoietic tissue necrosis virus.

Vertical transmission: eggs and semen of infected parent fish are more likely to be transmitted by eggs; horizontal transmission: water pollution, etc. The virus mainly invades the fish through the Gill and digestive tract.

Symptoms the disease often causes sudden mass death in the fry and juvenile stage, and usually occurs 7-14 days after infection. The diseased fish swims slowly, rotates, sometimes sinks to the bottom, the body color becomes black, the abdomen is dilated, the fin base is congested, the anal suspension is opaque, mucous feces, and the lateral muscles show "V" shaped bleeding. Fish with chronic diseases often have protruding eyeballs.

The epidemic and damage are mainly harmful to salmon fry such as salmon, salmon, river trout and other fry in the same year. The incidence is the highest when the water temperature is 4 ℃ ~ 13 ℃ and 8 ℃ ~ 10 ℃. The mortality of fry under 2 months old is 100% when the water temperature is 10 ℃. The mortality rate of fry aged 2 months to 6 months is more than 50%, and that of fry older than 7 months is about 10%. In recent years, it has been found that there are also cases of rainbow trout in the range of 7 grams to 100 grams.

Prevent strict disinfection of breeding facilities and tools; fish eggs are soaked with polyvinylpyrrolidone iodine (containing 1% available iodine) 50 mg / L for 15 minutes, but the concentration can be increased to 60 mg / L when pH is alkaline, because the effectiveness of polyvinylpyrrolidone iodine is reduced under alkaline conditions; diseased fish are destroyed thoroughly; and fish fry ponds are located at the upstream of the hatchery.

The serious deterioration of the disease could be controlled by raising the water temperature of the diseased fish pond to 17 ℃ ~ 20 ℃. In addition, the feces dragged by the anus of fish with infectious hematopoietic tissue necrosis disease are thicker and longer than those of fish with infectious pancreatic necrosis disease.

 
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