Eel Summer Syndrome Causes Severe Mortality, Farmers Need to Take Preventive Measures

Since the beginning of summer, eel ponds across Fujian Province have successively experienced comprehensive diseases such as eel slime loss and septicemia, causing severe eel mortality. Based on some cases we handled on-site in southern Fujian, the following prevention and treatment methods are hereby proposed for the reference of eel farmers.

The symptoms of this disease are as follows: in the early stage of mortality, diseased eels show obvious slime loss or septicemia symptoms. Eels have weakened vitality, with large numbers hanging on feeding platforms or gathering around drainage outlets, and they do not feed. Among dead eels, slime loss symptoms are not numerous, while septicemia symptoms are more obvious. Because the number showing slime loss or septicemia symptoms decreases in the later stage, red head or congestion and edema of the gills and lower jaw are more commonly seen, while other body surface areas remain basically intact; in some cases the abdominal cavity is filled with bloody fluid; there are blood clots, the liver is discolored, and the gill filaments turn white and swollen, showing a phenomenon similar to discoloration and whitening after being soaked in water. The number of deaths increases very rapidly, and the mortality rate is relatively high. The entire disease cycle in one pond lasts 15 to 20 days.

Effective treatment:

Salt + Chinese herbal medicine + antibiotics, with salinity maintained at 4‰ to 7‰. The main Chinese herbal medicines include Coptis chinensis, rhubarb, Scutellaria baicalensis, Humifuse Euphorbia Herb, Artemisia capillaris, and Chinese gallnut, etc. For antibiotics, doxycycline, norfloxacin, flumequine, etc. may be selected. The medication cycle requires 1 to 2 courses of treatment, and severe cases may even require 3 to 4 courses.

Points to note:

Treatment of pond water. Because medication may need to be used for a long time, it easily causes water quality deterioration. Therefore, after each medication cycle ends, it is best to carry out a large water exchange to keep the water environment clean.

During high-temperature periods, pay attention to changes in water temperature and water quality. Generally, ventilation should be strengthened, dissolved oxygen in the water should be increased, and when necessary the water level should be raised for medication, to prevent a sharp change in water temperature during medication from increasing eel mortality.

In the early stage of the disease, the use of antibiotics also cannot obviously inhibit the progression of mortality. Conventional disinfectants such as bromochlorohydantoin, chlorine dioxide, and Blue Angel + Virus Net may be chosen first to control the progression of the disease. If relatively large numbers of deaths occur, then use the methods described above.

After the peak mortality period has passed, the surviving eels in the pond must be encouraged to feed as early as possible to restore their strength. Medicated bait can be fed to eliminate pathogenic bacteria in the eels' bodies. At this time, for disinfection of the water body, it is necessary to use drugs with low irritation. At the same time, Haizhongbao, multivitamins, glucose, etc. can be used for water baths for the eels to promote feeding.

While dealing with bacteria, attention should also be paid to checking whether there is branchiomycosis and parasitic disease. If present, they should be treated first, and especially branchiomycosis must be killed first. Otherwise, when antibiotics are used, branchiomycosis may break out and cause large numbers of deaths. If the number of parasites is not large, treatment may be temporarily postponed.