How to effectively treat autumn gill rot disease in carp
1. Incidence and symptoms
In 2005, a total of 8 cages of carp were farmed in Tumenzi Reservoir. From the introduction of fry at the end of April to mid-September, disinfectants were consistently applied externally by splashing or hanging baskets every half month, and medicated bait was fed once every 20 days. Bactericides and insecticides were used alternately for prevention. No fish disease was found in the early stage of farming. Based on past experience, disease rarely occurred in autumn, so prevention was neglected. The disease broke out starting on October 1. From October 1 to 3, each cage lost as few as 1 fish and as many as 3 to 5 fish per day, with daily deaths reaching 10 to 15 kg. From October 4 to 8, each cage lost as few as 3 to 5 fish and as many as 8 to 10 fish per day, with daily deaths reaching 20 to 30 kg. From October 8 to 11, after treatment, the number of dead fish decreased day by day, and by October 13 the disease was basically brought under control. The main symptoms of diseased fish were: slow swimming, poor appetite, and darting up and down. Upon retrieving dead fish for observation, some had rotting gill filaments, some had petal-shaped gills, and some had open skylights. As this was a grassroots unit, no microscope was available for definitive diagnosis. Based on past experience and the comprehensive conditions of reservoirs in the region, a treatment approach combining insecticidal and bactericidal treatment was adopted.
2. Treatment methods
1. Disinfectant treatment From October 3 to 5, a mixture of copper sulfate and ferrous sulfate (5:2) was splashed at a concentration of 2 g/cubic meter (water volume calculated based on the water inside the cages). Since drugs splashed in cage culture easily diffuse, the dosage was increased, and the same applies to the use of trichlorfon described below. From October 6 to 11, long-acting trichlorfon was splashed at a concentration of 1.25 g/cubic meter.
2. Oral medicated bait treatment Starting from October 6, medicated bait was fed. The medicated bait was made into pellets by the feed manufacturer directly adding the drug to the feed. The fish drugs used were Baoji'an (fish-use type) mixed with Bingdujing. The main ingredient of Baoji'an is levofloxacin, used at 1 g/kg of feed. The main ingredients of Bingdujing are ribavirin, enrofloxacin, and VC, used at 2 g/kg of feed.
After combined internal and external treatment, the disease was basically controlled by October 13. After October 15, no more dead or diseased fish were found, and the fish disease was basically cured.
3. Observations
Gill rot disease is a relatively common fish disease that spreads rapidly and has a long course. Once it breaks out, it is difficult to control its spread. There are mainly two types of gill rot disease: parasitic gill rot disease and bacterial gill rot disease. Prevention in the early stage of farming was good, and no fish disease occurred. In the later stage, due to neglected prevention, the fish became ill, causing unnecessary losses. Therefore, in the process of farming, prevention should be given priority, with prevention valued more than treatment, and precautions taken before problems arise.