Mandarin fish, also known as osmanthus fish, crucian carp and Eriocheir sinensis, is one of the "four famous freshwater fish" in China. It is a carnivorous and solitary benthic freshwater fish. Because of its strong adaptability to water temperature, it is cultivated in all major aquaculture areas in China. May -65438+ 10 is the period when mandarin fish are prone to epidemic diseases. Common diseases, such as trypanosomiasis, dactylosis, trichinosis and bacterial diseases, are the key factors affecting the survival rate of young fish. How to reduce the incidence? The key points are to stabilize water body, prevent blister disease, control "three highs", enhance immunity, disinfect regularly and eliminate pathogenic bacteria. The most important thing is to use "killer" drugs with caution.

1. Basic information: A 5-mu pond for Siniperca chuatsi fry, with an average water depth of1.3m.. On May 8th, put 1.6 million mandarin fish fry, impeller aerator 1. The average size of fry is 5-6 cm. In order to prevent and eliminate parasites and zooplankton, metronidazole (mainly composed of cyanopentyl polyester) was used for three consecutive days in the morning, with a dose of 250ml (2 and a half bottles per bottle 100ml). Recently, the weather has been rainy and rainy, and the average water temperature is around 20℃. It was found that some fry swam slowly on the water alone, and 2-3 fish swam together. When they were fished out, they found that the rotten caudal fin was bloodshot and red around the gill cover, under the jaw and at the root of the fin, and its vitality was poor. The water quality index was determined, and the water quality was brown, with PH value of 8.0, ammonia nitrogen of 0.2 and nitrite of 0.0 1. After electrolysis in electrolytic cell, it was preliminarily judged as poisoning.

Case study: 1. Bubble disease is a common problem in the early stage of Siniperca chuatsi fry cultivation. The partial pressure of gas in water exceeds the partial pressure of gas in the body, which leads to small bubbles in the soft tissue or gill outside the fin. The fry stage is a period of weak immunity, which will lead to bacterial diseases and then lead to rotten fins.

2. The content of unsaturated fatty acids around gill cover, submandibular and fin root is high, and ammonia nitrogen appears at seedling stage, while molecular ammonia is easily soluble in fat, and bacterial infection causes redness.

3. Excessive use of fenvalerate will corrode the gills and liver of fish, while Siniperca chuatsi is a benthic fish. When sleeping at night, it is easy to float on the water only when it is in the gills or poisoned.

Three. Handling suggestions:

1, water stability is the key in the fry cultivation stage. On the premise of water conservation, regular use of "Haodujing", "Li Shen Carbon" and "Algae Essence" can effectively stabilize the physical and chemical indexes of water bodies and prevent the occurrence of blisters.

2. Parasitic diseases, especially Trichinella spiralis and rotifers, are the most harmful in the fry cultivation stage. Many farmers use chemicals such as copper sulfate, formaldehyde or pyrethroids, which will not only destroy the ecological environment, but also kill algae and play a bactericidal role. When parasites appear, it is best not to use irritating and toxic products, which will seriously affect the health of fry. When parasites appear in vivo or in vitro, they can be taken orally with pure Chinese herbal medicines "Wan Lei Areca Powder" and "Sophora Flavescentis Powder", and added and subtracted with "Fudi" and "Chaoneng Granule".

3. Clean the pond correctly and thoroughly when entering Tangqian: first use pesticides, then bleach 50-80 kg/mu, and finally clean the pond with lime 150-200 kg/mu of water. Before stocking fry, soak them in 1% povidone iodine solution (mirex) or bdellovibrio bacteriophage solution (Supreme 95 or Supreme 99), and then sprinkle "Supreme 99"+"Good C100"+"Carrefour" all over the pond.