Infectious pancreatic necrosis of salmon and trout
The pathogen is infectious pancreatic necrotic disease virus.
Vertical transmission: eggs and semen of parent fish with virus; horizontal transmission: feces, urine and secretions of diseased fish bring the virus into the water, the route of infection is Gill and mouth.
Most of the juvenile fish with symptom weight more than 5 grams are chronic, the speed of death is slow, the appearance of abdominal swelling, blackening of body color, exophthalmos, hyperemia and redness of fin base and abdomen, anus mostly dragging linear feces, slow swimming and poor feeding. Most of the fry weighing less than 5 grams are acute, the speed of death is fast, the activity of diseased fish is slow, the bottom sinks after swimming sideways or slowly, the abdomen expands, and the body color turns black.
The epidemic and harm of the disease mainly harms the fry and larvae of salmon fishes. 2-month-old seedlings often cause acute mass death, generally 7 weeks after feeding began to die, larger fry first disease, more than 20-week-old young fish generally no longer disease. The water temperature of the disease is 10 ℃ ~ 15 ℃, and the mortality rate can reach 80% ~ 100% when the water temperature is 10 ℃ ~ 12 ℃. The incubation period of the disease is related to fish size and water temperature. The bigger the fish, the longer the incubation period, and the higher the water temperature, the shorter the incubation period.
Prevent the reproduction of larvae of parent fish without pathogens, do not transport fish and eggs from the affected areas, use independent water bodies for spawning, hatching and culture, fish fry and fry should be placed in the upstream of fishing grounds to prevent horizontal transmission, prevent water pollution, disinfect sick and dead fish in time, thoroughly disinfect fish facilities and tools with high concentration of chlorine, and disinfect fish eggs with polyvinylpyrrolidone iodine 50 mg / L for 15 minutes.
The treatment pool generally controls the development of the disease by raising the water temperature.
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The effect of rare earth feeding on fish is good.
Rare earth refers to the general name of 17 metal elements in the periodic table, including lanthanum, praseodymium, neodymium, cerium, samarium and so on. Among them, cerium accounts for 48%, lanthanum 25%, neodymium 16%, praseodymium 5%, samarium 2%, and other 12 elements 4%. In recent years, rare earth has become an important resource for national economy and national defense construction. Not only can it be widely used as an industrial vitamin in metallurgy, machinery, petroleum, chemical industry, light industry, electronics and other industries, but also can be used as micro-fertilizer in agricultural production. In fishery production, feeding rare earths to fish also has a very good effect. According to the test
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What is the "sexual transformation" of female swordtail fish?
The so-called "sexual transformation" of female fish refers to the gradual masculinization of some female fish that have given birth to larvae: the body becomes slender, sword-shaped protuberances grow under the caudal fin, and the anal fin turns into a rod-shaped mating device, and begins to chase the female, mate and fertilize with it, and reproduce. However, only the female changed from male to male, and no male to female was found. Recently, different opinions have been expressed on this issue: swordtail fish cannot be reversed sexually, and their natural sex ratio has always been between 1:2 and 1. 5. Although the larvae of swordtail fish grow to 3 months, the reproductive organs of both sexes open.
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