Prevention and Treatment Methods for Gas Bubble Disease in Overwintering Common Carp Aquaculture

June to September is the peak period for fish disease outbreaks. In adult fish ponds, hemorrhagic septicemia of crucian carp frequently occurs and endangers silver carp, bighead carp, and blunt snout bream, causing heavy losses to farmers. Conventional medication generally produces poor therapeutic results. After years of repeated observation and treatment, researchers have explored some new methods and experiences, which are introduced below for reference. (1) Medicated feed made with 20 g furazolidone or oxytetracycline per 100 kg of fish, fed continuously for 3 days as one treatment course. (2) 0.5 ppm strong chlorine (trichloroisocyanuric acid) dissolved in water and splashed over the entire pond. (3) Mixed treatment: On day 1, splash 0.5 g of sodium dichloroisocyanurate per cubic meter of water over the entire pond, and withhold food for 1 day; from day 2 onward, use 8 g sodium dichloroisocyanurate, 4 g furazolidone (human use), 5 g oxytetracycline, and 100 g table salt per kilogram of concentrated feed, crush and mix with water, stir evenly and feed, once daily for 3 consecutive days. (4) Comprehensive treatment: For every 667 sq m of water surface with a water depth of 1 m, use 2 kg tobacco leaves, 14 mL deltamethrin (Decis), 333 g copper sulfate, and 270 g dried Isatis root (Isatis indigotica). Usage: First place the tobacco leaves in a large iron pot and boil; after 2 hours, splash the liquid over the entire pond. Then pour deltamethrin into a wooden basin, dilute with water, and splash over the entire pond. On the morning of day 2, first decoct Isatis root in water, pour into a wooden basin, dilute with water, and splash over the entire pond. Then dilute copper sulfate and splash over the entire pond. After 3 to 4 days, the diseased fish recover.

Precautions: (1) The above treatments are for reference only. Efficacy should be verified before formal promotion. If a large number of fish become sick before verification, consult technical personnel. (2) If fish have parasites, they must first be killed with medication, then treated according to the above methods. (3) After medication, do not immediately seine or drain the pond, to avoid injuring the fish and accelerating infection.

In late January 2004, gas bubble disease occurred in an overwintering pond for adult common carp in Baodi, Tianjin. The basic situation was as follows:

The pond was about 10 mu, with ditch water as the water source, mainly culturing common carp. The fish that fell ill and died included common carp and grass carp. The average weight of common carp was 1.5 kg per fish, and the average weight of grass carp was 1 kg per fish. The pond water had already frozen, but some areas had not frozen because diseased fish swam back and forth. Some fish had bubbles filling the skin between fin rays, at the base of the tail fin, and under the epidermis at the tip of the snout. There was red hemorrhage on the bodies of dead fish, with an average of 5 to 6 fish dying per day. Test results for ammonia nitrogen and hydrogen sulfide were normal; only dissolved oxygen severely exceeded standards, leading to a diagnosis of gas bubble disease.

Gas bubble disease occurs when dissolved gases in water (such as oxygen, nitrogen, and hydrogen sulfide) are too high, but it is mainly caused by excessively high oxygen content in the water. In this case, a large amount of ditch water had been injected into the pond before overwintering. The water quality was relatively fertile, with much organic matter in the water, and planktonic algae reproduced in large numbers, causing the oxygen content in the water to be too high and leading to disease. After winter set in, the pond water froze, making fish activity difficult to observe. After the fish were found to be diseased, the farmer first splashed salt continuously for 3 days (7 g per cubic meter), but because the condition was relatively severe, the effect was poor. Then a method of splashing copper sulfate over the entire pond was adopted, using 0.7 g per cubic meter of water; after 2 to 3 hours, splash Yuxiale at 0.3 to 0.4 g per cubic meter of water; after an interval of two days, splash each again after three more days, for three consecutive applications, and only then did the condition stabilize. Under normal circumstances, people only pay attention to increasing dissolved oxygen in the pond but neglect the harm of excessively high dissolved oxygen. Although adult fish have a relatively low probability of developing gas bubble disease and the mortality rate is not high, if the condition is severe, it can still cause some losses, so it should not be taken lightly.