The eel is an important freshwater economic fish in China. Its meat is delicious and highly nutritious, and it is deeply loved by consumers. With the increasing market demand for eels, artificial breeding has developed rapidly, and intensive and large-scale production has become the mainstream trend.
According to the "2024 China Fisheries Statistical Yearbook", the total output of yellow eels in China has reached 355,000 tons. Among them, the output of Hubei, Jiangxi, Anhui, Hunan and Sichuan provinces accounts for approximately 96.4% of the national total. Hubei Province has the largest output, accounting for about 47.8% of the national total.
There are various farming models for yellow eels, mainly including pond cage farming and integrated rice-eel farming, among which pond cage farming is currently the most important farming model. However, with the expansion of the breeding scale and the increase in density, the problem of diseases has become increasingly prominent, becoming the main bottleneck restricting the sustainable development of the eel breeding industry.
The diseases of eels are characterized by rapid onset, rapid spread and high mortality rate. Once the disease occurs, the treatment effect is often unsatisfactory, causing significant economic losses to the farmers.
This article will provide a detailed introduction to the most common disease types, symptoms and scientific prevention and control measures in the process of eel farming, helping farmers increase the survival rate of eels and achieve efficient farming.
Bacterial sepsis
Bacterial sepsis is a serious disease caused by Gram-negative bacteria such as Aeromonas hydrophila and Aeromonas virginii. This disease has a wide prevalence and a long season. It is prone to occur from June to September and can occur at water temperatures ranging from 10 to 35 degrees Celsius.
Typical symptoms: Diseased eels float on the water surface or lie prone on aquatic plants, refuse to eat, and respond slowly to external stimuli. Red spots of varying sizes appear on the body surface (especially on the sides and abdomen), which do not fade under pressure. Some diseased eels have red and swollen heads, with blood flowing out of their mouths and gills, and their anus is also red and swollen. Post-mortem examination revealed extensive hemorrhage in the internal organs and bloody bodies in the abdominal cavity.
Prevention and control measures:
External disinfection: Sprinkle povidone-iodine solution or bromopovidone-iodine solution throughout the pond
Oral medication: Feed with enrofloxacin powder, doxycycline hydrochloride powder or florfenicol powder
Chinese herbal medicine as an aid: Chinese herbal medicines such as Rhubarb and Gallnut Powder can be added to the feed for feeding
Management measures: Strengthen monitoring for early detection and early treatment; During the treatment period, the aerator was operated to ensure dissolved oxygen. Timely salvage dead fish and carry out harmless treatment; Regulate water quality and sediment; Avoid the frequent and large use of disinfectants
Bacterial enteritis
Bacterial enteritis is mainly caused by Aeromonas intestinalis punctate, and the peak period of incidence is from July to September. Feeding stale bait or feeding irregularly is the main cause.
Typical symptoms: The sick eel has a reduced appetite, swims slowly, and sometimes shows the phenomenon of "grass crawling". In severe cases, the body color is blackish blue, the anus is congested, red and swollen, and protrudes outward. When the abdomen is gently pressed, yellowish red mucus flows out. Dissection reveals intestinal inflammation and congestion. Generally, there is no food in the intestinal tract.
Prevention and control measures:
Prevention first: Ensure the freshness of the feed, feed reasonably based on the eating situation, and remove leftover feed in a timely manner
Traditional Chinese medicine prevention: Add 2g of fish Sanhuang Powder (Rhubarb, Scutellaria baicalensis, Phellodendron amurense) per kg of feed for feeding, once every 15 days, for 3 to 5 consecutive days
Western medicine treatment: Mix 30-50g of allicin with every 50kg of eel and feed it for 3 consecutive days. Or, apply 0.2-0.3g/L of erythromycin for poultry throughout the pond. At the same time, mix 1g of compound sulfamethoxazole with 50kg of eels for feeding once a day for 4 consecutive days
Water quality management: Disinfect with bleaching powder every 10 to 15 days during the disease season
Saproderma
The skin rot disease is caused by the infection of the punctate subspecies of Aeromonas punctate on injured or weak eels. It is one of the main diseases of adult eels, with a high incidence from May to September.
Typical symptoms: Circular or oval ulcer foci of varying sizes appear on the body surface, surrounded by congestion and redness. In severe cases, the ulcers deepen into funnel shapes and may even ulcerate to the bones.
Prevention and control measures:
Pre-treatment before stocking: Disinfect the pond water with 20-25g/L quicklime, and strictly screen and eliminate injured and diseased eels
Management during the onset season: Replace one-third of the pool water every 2-3 days and sprinkle 1-2g/m³ of bleaching powder throughout the pool
Traditional Chinese medicine treatment: Sprinkle 2-4mg/L of gallnuts throughout the entire pond. At the same time, mix 2g of sulfamethazine with 100kg of eels for feeding. Continue feeding for 5-7 days
Water mold disease
Water mold disease is a common disease caused by fungi such as water mold, mainly occurring in spring and autumn when the water temperature is between 10 and 18 degrees Celsius.
Typical symptoms: At the onset of the disease, the symptoms are not obvious. A few days later, grayish-white cotton-like mycelium of water mold adheres to the affected area. Sick eels often show signs of restlessness, frequently exit their burrows and swim slowly alone. The muscles at the affected areas decay, they lose their appetite, gradually become emaciated and eventually die.
Prevention and control measures:
External treatment: Use veterinary drugs such as Compound nail Cream Spirit Powder for treatment
Salt and soda mixture: Sprinkle 0.04% salt and 0.04% baking soda mixture throughout the pond
Soaking in potassium permanganate: Soak the diseased eels in a 2mg/L potassium permanganate solution for 3 to 5 minutes, once every other day, for several consecutive times
Preventive measures: Avoid injury to the eel during operation; Before stocking, soak the eel species in a 3%-4% salt water solution.