Prevention and Treatment Methods for Several Gill Diseases in Whiteleg Shrimp (Litopenaeus vannamei) Farming
1. Gill disease caused by Vibrio.
Diseased shrimp float and swim slowly on the water surface, with gill filaments slightly swollen and dark gray, showing degeneration and necrosis at the tips. Under high magnification, actively motile bacterial cells can be seen. Ponds where this disease occurs have severely polluted bottom sediment and poor water quality, and the disease peak season is from July to September.
Prevention and treatment methods: (1) Remove excess sludge, keeping it at about 10 cm, thoroughly clear the pond with quicklime and freeze and dry the pond so that organic matter at the pond bottom is fully decomposed. (2) During farming, apply bottom-improving agents such as zeolite powder and Haizhongbao to change the anaerobic state at the bottom and stabilize the pH value of the bottom layer. (3) Use microbial preparations such as photosynthetic bacteria, EM bacteria and biological water-protecting agents to regulate water quality and inhibit the reproduction of Vibrio. (4) Treatment: splash dibromohydantoin over the whole pond at O.39/m³. Add 0.1% allicin or 0.3% oxytetracycline to the feed and use continuously for 5 to 7 days.
2. Gill disease caused by protozoa
Sessile ciliates and suctorians are a type of attached organism, mainly including Carchesium, Vorticella, Epistylis, Stentor and suctorians, whose adult stages often attach to shrimp gills and body surface. When their numbers are large, a layer of gray-black downy material can be seen on the shrimp surface, dirty and unsightly, and the gill area turns black. This affects the shrimp's respiration and normal growth and development, and in severe cases causes difficulty in molting. Diagnosis can basically be made from external symptoms, and confirmation is made by observing a large number of parasites under low magnification.
Prevention and treatment methods: (1) Because the water has a high organic matter content and the pond water is very fertile, water quality can be regulated by changing the water; cultivate an appropriate amount of phytoplankton to regulate the water ecological environment. (2) Many farmers splash tea seed cake to stimulate shrimp molting to solve this problem, but molting stimulated by tea seed cake is abnormal molting. Therefore, after stimulating molting, mineral elements, especially calcium and phosphorus, need to be added to the feed at 2% of the feed, and nutrition should be improved. Moreover, this method cannot be used frequently, otherwise it will affect the shrimp's immunity. (3) Splash zinc sulfate over the whole pond at O.5 to lg/m³. (4) Every other day, splash dibromohydantoin over the whole pond at 0.2 to 0.39/m³ or Xinjieer at 0.5mL/m3³, and add 0.1% allicin to the bait.
3. Gill disease caused by filamentous bacteria
The gill area of shrimp is dark brown, with poor appetite, slow growth and difficulty in molting. The pathogen is Leucothrix mucor, which reproduces by conidia; the hyphae are filamentous, unbranched, slightly thicker at the base and thinner at the tip. During diagnosis, a large number of hyphae can be observed under high magnification, with the thicker end attached to the gill area and the thin end free. This disease is likely to occur under conditions of high farming density and fertile water.
Prevention and treatment methods: (1) Control the fertility of the pond water and reduce the organic matter content. (2) Reduce leftover bait and prevent pollution of the bottom sediment and water quality. (3) Splash chelated copper over the whole pond at 0.59/m³ or methylene blue at O.1 to 0.29/m³, and at the same time feed florfenicol orally mixed into the feed at 1 to 29/kg feed, continuously for 5 days.
4. Gill disease caused by poor water quality
In the middle and late stages of farming, the pond water load is heavy, and harmful substances often accumulate. In addition, under the influence of severe weather such as typhoons, rainstorms and cold air, abnormal conditions such as water stratification, convection and bottom sludge stirring up occur in the pond water. The deterioration of the water environment often causes pathological changes in gill tissue, necrosis and yellowing or blackening, and adhesion of foreign matter, and sometimes the shrimp body is slightly red.
Prevention and treatment methods: (1) Frequently measure water quality and keep track of changes in pond water quality. Use quicklime at 5 kg per mu or Jiangjian Gaishuiling at 0.5 to lg/m³ to adjust pH, and every 10 to 15 days use compound microbial preparations such as EM preparations and biological water-protecting agents to control the dominant populations of algae and microorganisms in the pond. Absorb and transform various reducing substances, playing a good role in stabilizing and repairing water quality. Keep pH stable at 7.8 to 8.5, ammonia nitrogen less than 0.5 mg/L, and nitrite nitrogen less than 0.1 mg/L. (2) Severe weather such as rainstorms or continuous cloudy and rainy days will cause strong stress responses in shrimp, causing a decline in shrimp immunity. Measures such as increasing oxygen, changing water and splashing water purifiers should be used to control water changes, and according to weather forecasts, 0.2% Vc and 1% shrimp Genlian Jiedu San should be added to the feed in advance.
5. Gill disease caused by malnutrition
When the feeding amount is small or the bait lacks nutrients, the shrimp become weak and develop the disease. Due to lack of Vc and other factors, melanin deposits in the gill area, which then ulcerates, necroses and turns black. During diagnosis, necrosis can also be seen in the shrimp stomach wall, hindgut wall and liver, especially in the body segments and appendage joint membranes.
Prevention and treatment methods: (1) Master the appropriate feeding amount and improve the nutritional composition of the feed so that the formula meets the nutritional requirements of whiteleg shrimp. (2) Add 0.3% Vc and 0.2% molting hormone to each kilogram of feed.