What are the key technical points of Taishan eel farming in earthen ponds?

The Taishan earthen pond eel farming model is an extensive farming model developed by referring to the earthen pond farming model for Chinese carp. Its characteristics are: ① The ponds are large, generally more than 4 mu, up to 20-30 mu, and developed in contiguous tracts; ② The stocking density is low; ③ Water sources are insufficient, and the water is used for a whole grow-out cycle, with a water depth within 1.2 m; ④ The soil quality is good, mainly loam; ⑤ Aeration facilities are fully equipped; ⑥ The feeding method is to feed to satiation at every meal until feed remains; ⑦ The annual grow-out rate is above 90%.

Taishan earthen ponds are mostly developed from land created by reclaiming land from the sea and enclosing it into fields. The soil is mostly loam, with very good water retention performance. Over a year or eight or nine months, apart from some evaporation, the water in a pond almost does not seep away. Therefore, almost no new water needs to be added throughout the entire farming process, and the water quality is extremely stable. As for how to raise a pond of eels well, the key technical points are as follows:

1. The ponds for Taishan earthen pond eel farming are pure earthen ponds and are not equipped with supporting whitebait fry nursery ponds. The eel fingerlings stocked come from contract nursery rearing in the Jiangsu and Fujian areas. In response to this situation, Taishan eel farmers set up "mother ponds" and "daughter ponds." The so-called "mother pond" means directly putting in the well-trained small-sized eel fingerlings (generally 150-200 fish/kg) at a stocking density of 20,000-30,000 fish/mu. After one cycle of rearing, seine nets are used and the large-sized eels are selected out and put into the so-called "daughter ponds" until they are grown into marketable eels. The small-sized eels left after screening continue to be reared in the original pond. After 2-3 screenings, very few undersized eels remain. At this point, the "mother ponds" can be cleared and counted, and fingerling rearing is basically finished. Why set up "mother ponds"? The significance lies in this: because the number of "mother ponds" is small, and the small-sized eel fingerlings are stocked at high density in the "mother ponds," this can reduce the undersized eels to only a small number of "mother ponds."

2. Preparation work for the pond before stocking. After the pond bottom is sun-dried until it cracks (or the cracked layer is pushed away with a bulldozer), water is added to the farming water level. Quicklime is used at 400 kg per mu, mixed with water, and splashed over the entire pond. The aerators are turned on to stir it evenly. After 10-15 days, 25-30 kg/mu of tea seed cake is used to kill wild trash fish and shellfish, etc. After another 7-10 days, 200-300 g/mu of cypermethrin and 2-3 kg/mu of trichlorfon are added to kill parasites and zooplankton. Under normal circumstances, after another 7-15 days, the water can be tested and eels can be stocked. At this time, the pond water is "mung bean green" in color and is "fresh, lively, tender, and crisp." After the eel fingerlings are put in, they can immediately come to the platform to feed.

3. Because Taishan earthen pond eel farming is developed in contiguous tracts, the water supply is insufficient; water relies on pumping, and farming costs are high. Therefore, eel farmers do everything possible to shorten the farming cycle, and when possible, raise the eels in one pond of water until finished products are produced, with almost no water exchange in between. To shorten the farming cycle, they use an unrestricted feeding method, that is, letting the eels eat to satiation, with the standard being to feed at every meal until the eels stop eating. ① Throughout the feeding process, to prevent indigestion, a large amount of digestive enzymes is added to help the eels digest and absorb, and enough aerators are turned on to ensure sufficient dissolved oxygen. ② A large amount of fish oil is added to provide part of the calories needed for the eels to put on fat, thereby improving feed efficiency. ③ During the rearing of small-sized eel fingerlings, oral growth promoters such as "Qiangzhuangsu" and drugs that enhance immunity are added, so that the eels grow healthily and rapidly.

4. Always maintain the stability of the pond water: ① Keep the pH value of the farming pond water between 8.2 and 8.8. On sunny mornings, the pH value should not be lower than 8.2, and in the afternoon it should reach 8.8 or above; otherwise, adjust it with quicklime. ② When applying medicine, strive to dilute it extremely and splash it over the entire pond, so that the eels will not have a stress reaction due to excessively high local concentration or too great an instantaneous change in pond water concentration. ③ Cultivate a microecological environment dominated by green algae and always maintain its vitality. This requires technical personnel to attach great importance to the periodic changes in the farming pond water and to kill zooplankton and some aged algae at the appropriate time. ④ Keep the pond water level at about 1.2 m, and through the dual mixing action of paddlewheel and spiral aerators, break the "thermocline," so that dissolved oxygen enters the bottom layer and the production of harmful substances is reduced. ⑤ Once an epidemic occurs, it is necessary to use highly effective medicines, and also insist on not draining the water, precisely to maintain the stability of the pond water.