When spring and summer temperatures fluctuate, beware of parasitic diseases in koi farming

Spring is the season when all things revive. When the water temperature reaches above 10°C, koi begin to move and feed, entering the normal stage of growth and development. But at the same time, March to April each year is a period of relatively intense weather changes throughout the year, just as spring turns to summer. The temperature rises noticeably, and because overcast days and plum rain frequently occur in this season, rainfall increases noticeably, light is insufficient, air pressure is relatively low, and temperature fluctuations are relatively large. Cold waves and strong cold air often have an impact, and sudden cold and warm weather is common, which easily causes increased stress responses in pond-cultured koi and leads to a gradual increase in fish diseases. Especially in the Pearl River Delta region, the first peak period for fish diseases generally arrives in late March each year.

According to feedback from some farmers in Lecong Town and Longjiang Town in Shunde, since April this year, koi in some farms have developed various parasitic diseases, especially trichodiniasis, which is relatively serious. Parasitic infestation of koi affects their appearance and reduces their ornamental value. Therefore, active prevention and control are needed. Usually pay attention to regulating water quality well, and according to the specific situation use relatively mature insecticidal drugs for eradication. The following introduces the prevention and control methods for several common parasitic diseases of koi for reference. 1. Koi gyrodactyliasis: The body surface of diseased fish may be congested, or there may be localized mucus shedding and fading, and some gill filaments may be ulcerated. Microscopic examination shows Gyrodactylus on the gills. Traditional insecticides can effectively treat this disease. A mixture of potassium permanganate and crystalline trichlorfon (17:3) is splashed over the whole pond at a dosage of 1-2 ppm, and it still has a good effect at low temperatures. 2. Koi dactylogyriasis: Dactylogyrus generally parasitizes the gills of koi, damages gill tissue, and causes anemia and emaciation in the fish. The gill filaments of diseased fish have increased mucus, are swollen, and are wholly or partly pale, with signs of decay; the operculum is open, movement is sluggish, food intake drops sharply, breathing is difficult, sensitivity to external stimuli is greatly reduced, and the fish may even lose response, floating motionless at the water surface near the shore or darting and jumping sharply in the water. Prevention and control methods: (1) After onset, use a 20 mg/L potassium permanganate aqueous solution to soak the diseased fish for 15-30 minutes. (2) Splash mebendazole over the whole pond at a dosage of 15 grams per mu per meter of water depth, and do not add new water within 72 hours after medication. (3) Orally administer enrofloxacin medicated bait. For every 100 kg of fish, use 2 grams of enrofloxacin raw powder mixed into the bait each day, feed in three divided doses, with 6 days as one treatment course. (4) After the condition is brought under control, the diseased fish pond should be refilled with about 20 cm of new water. 3. Koi trichodiniasis: Trichodina mainly destroys the gill tissue of koi, affects fish breathing, and can cause death. After onset, diseased fish make rubbing-bottom movements and contract their fins. After the gills of koi are invaded by the pathogen, they tend to swim at the water surface or near the pond edge, resembling “floating head” behavior, the body becomes thin, the fish are sluggish, the body color is darker, and the fish body loses its luster. Prevention and control methods: (1) Salt bath method: Use a 1%-2% salt water solution to bathe diseased fish for about 10 minutes, once every other day, for 3 consecutive times. Keep the diseased fish quietly in a dedicated tank or pond and care for them carefully. (2) Potassium permanganate bath method: Dissolve 0.1 gram of potassium permanganate in every 5 kg of fish-rearing water, bathe the diseased fish for 15-25 minutes, once every other day, for 3 consecutive baths. Keep the diseased fish quietly in a dedicated tank or pond and care for them carefully. (3) Trichlorfon solution bath: Bathe diseased fish in a 0.2 ppm trichlorfon solution for about 1 hour, once a day. When splashing insecticidal drugs in fish ponds, arrange according to the fertility of the water body, weather, water temperature, and fish activity. Experienced farmers remind: when using medication, pay attention to controlling the dosage, and never overdose, otherwise it is easy to cause koi death. When the weather and water temperature are normal and the fish show no obvious abnormalities, the medicated water can be splashed at 3-4 p.m.; when killing parasites, special attention should be paid to observing the performance of the koi. If abnormal conditions such as frantic swimming, twitching, staying close to the edge, or floating head occur, immediately change 50% of the water and increase oxygen, then continue observing. It is especially important to note that after parasite killing is completed, antibiotics should immediately be used as a supportive treatment.