Precautions for Catching and Sorting during the Separate Rearing of Adult Eels

1. Catching

There are two methods for catching adult eels for separate rearing. In larger eel ponds, net catching is generally used; in smaller ponds or concrete-structured eel ponds, the pond water can be drained directly and the eels placed into an eel collection net cage.

With the net catching method, feed is used to attract the eels to the feeding area, and when most of the eels have gathered in the feeding area, the feeding area is surrounded with a net and the net is lifted at the feeding area. The caught eels are gathered in a long eel collection box. The long box should be positioned on one side of the eel pond where sorting operations are convenient, and 1 aerator should be installed 3 to 5 m from the long box. When the eels are placed into the long box, it should be started immediately so that pond water passes through the long eel collection box, allowing the water inside and outside the box to exchange continuously, preventing the eels from suffering oxygen deprivation due to crowding and affecting the separate rearing operation. At the same time, the netting should be constantly pulled so that the eels move about in the net cage, preventing the eels from being pressed against the bottom of the net cage and suffocating to death.

2. Cooling

For separate rearing and sorting when temperatures are relatively high in summer and autumn, the eels should be cooled with ice water, generally with the temperature controlled at 15 to 20°C. Through cooling, the eels' activity capacity is significantly weakened, so during sorting the eel bodies are less likely to be injured, and the sorting speed can also be increased.

3. Sorting steps and methods

Adult eel sorting generally uses manual picking, and manual picking is carried out on an adult eel sorting device. During sorting, first pour the cooled eels into the eel collection trough of the sorting device, then open the small sliding door on one side of the eel collection trough and let the eels swim out slowly. The operators sort according to the specifications required by the plan, and eels of each size grade gather through their respective channels into the pre-arranged net cages of each compartment. To make it easier for the eels to swim toward the net cages, the sorting device should be set up tilted slightly toward the pond.

4. Several issues to note in separate rearing of adult eels

(1) Separate rearing of adult eels should preferably be carried out on cloudy and rainy days. On cloudy and rainy days, the temperature is relatively low and the air humidity is high, so the eels are less likely to be injured during handling. In summer, when the weather is clear, separate rearing should preferably be carried out in the early morning or evening, and operations must never be carried out under direct sunlight.

(2) Sorting for separate rearing should strive for uniform specifications. In particular, for sorting adult eels for export, samples that meet the specifications can be pinned on the sorting device for operators to compare.

(3) All operations in sorting for separate rearing must be patient and meticulous, with gentle movements; avoid scratching the eel bodies during the operation.

(4) After separate rearing, eel fingerlings generally do not need disinfection when stocked, but if there are obvious scratches, disease, or a relatively long transport distance, then drug disinfection should be given. Generally, sulfonamide drugs are fed to the eels for 3 to 5 days, with the drugs mixed into the feed.