Problems in the black larval stage of Japanese eel and its countermeasures

At the turn of spring and summer, Japanese eel culture is mostly in the black larval stage, which generally reflects the decline of feeding rate, prone to rotten Gill, rotten tail syndrome and other phenomena, which seriously affect the healthy, sustained and steady development of Japanese eel culture. This paper analyzes the main problems existing in the culture stage of Japanese eel black larvae, and puts forward some countermeasures for reference.

(1) the feeding rate has decreased:

The feeding rate of Japanese eel black larvae decreased or the feeding amount was difficult to increase. The main inducing factors were unstable water quality, hepatobiliary problems, sporidium parasitism, enteritis, Gill congestion and inflammation, environmental stress, and so on. Breeders can take corresponding measures to deal with them according to different incentives:

Reason one: the water quality is unstable. Some breeders lack Japanese eel culture experience, copy European eel culture methods, daily water quality management is accustomed to a large number of water change, do not pay attention to algae culture in pond water, resulting in clear and thin pond water, transparency above 30cm, insufficient dissolved oxygen in culture water, which is not conducive to the feeding and growth of Japanese eel.

Countermeasures: properly reduce the amount of water exchange, use spirulina 3-5kg/ mu + compound fertilizer 2-3kg/ mu or diaosin 0.6-1ppm or rehydrin 1ppm, sprinkle the whole pool to cultivate water quality, and take VC3-5g/kg + heparin 5-8g/kg at the same time.

Reason two: hepatobiliary problems. Diseased eel bile secretion imbalance, anatomy found gallbladder atrophy, congestion around the liver or bile black, gallbladder enlargement (this condition is usually caused by drug poisoning).

Countermeasures: give priority to detoxification of water quality, if the pool water is sour, sprinkle with fresh water 2-3ppm, whole pool; if water is alkaline, use Shuibao 1-2ppm, sprinkle the whole pool; at the same time, take heparin 5-8g/kg + Xiaozhongzhixue 5-8g/kg material, 10 days as a course of treatment.

Reason 3: sporidia (also known as bipolar worms) are caused by parasitic kidneys.

Countermeasures: oral administration of Chong Di Zhi Spore Powder (Ling) 3g/kg material + heparin 5-8g/kg material, days as a course of treatment.

Reason 4: enteritis. There are generally three symptoms of bacteria, pullorum or colitis.

Countermeasures: first take Yukangbao (sarafloxacin hydrochloride) 5g/kg material + Changyanling (Chuanxinlian powder) 3g/kg material for 7-10 days, and then use BD-602 (eel-specific probiotics) 3-5g/kg material for 10 days as a course of treatment.

Reason 5: eel Gill congestion and inflammation. Sick eels often show that they like to flush (climb) aerator foam.

Countermeasures: external application of potassium permanganate 2-3ppm + Chongdizhisan 3ppm + Chongling 2ppm, sprinkle all over the pond; oral administration: heparin 5-8g/kg + Xiaozhongzhixue 5-8g/kg.

Reason 6: external environmental stimulation. If the water quality is too thin, sunny days are easy to be stimulated by sunlight, resulting in bait, bite phenomenon, or pool water ammonia nitrogen, nitrous acid on the high side.

Countermeasures: to cultivate water quality, use 1-2ppm or 0.3-0.5ppm (which can reduce NO2- and NH3+ in pool water), sprinkle it in the whole pool, and take VC3-5g/kg material internally.

Second, rotten Gill, rotten tail syndrome:

Reasons: improper operation of eel pond selection, resulting in mechanical damage, or deterioration of pool water quality (especially pool aging or cement bottom easy to occur).

Countermeasures: stop eating 1-2 meals, use potassium permanganate + oxytetracycline hydrochloride 8-10ppm or florfenicol (10%) 3-5ppm or 10%PVI 1ppm, sprinkle in the whole pool, 1-2 days after using fresh water 2-3 ppm + chlorine dioxide 0.2-0.3ppm, 2-3 times in a row.

Oral administration: compound vitamin B tablets 10-20 tablets / kg + sarafloxacin hydrochloride 5g/kg, 7-10 days as a course of treatment.

If the symptoms of rotten tail are more serious, try to reduce the water temperature, let the greenhouse ventilated, and stop eating 2-3 meals.

External use: salt 3-5 ‰ + oxytetracycline hydrochloride 10-15ppm, sprinkle in the whole pool, once in 16 hours, twice in a row; then adjust the water quality: fresh water 2-3ppm + chlorine dioxide 0.2-0.3ppm; take orally as above.