Seedling rearing and stocking techniques for eel farming

Eel seedling rearing is the production process of growing glass eels into eel fingerlings of more than 10 grams. This stage requires rearing through three different types of ponds: primary ponds, secondary ponds and tertiary ponds. Eel fingerlings are the foundation of adult eel farming; the quantity and quality of eel fingerlings directly affect the success of adult eel farming. Therefore, to develop eel farming production, the first priority must be to do a good job of eel seedling rearing. To ensure the smooth progress of glass eel rearing work, in addition to all the above preparatory work, the following production steps must also be carried out well.

Time for stocking glass eels

Since glass eels can only formally begin feeding and growing when the water temperature is above 15°C, for rearing eel seedlings in open-air ponds, it is more suitable to stock when the natural water temperature reaches above 13°C. In this way, after a short period of temporary holding to adapt to the environment, the glass eels can begin feeding and training once the water temperature rises. In Fujian and Guangdong in China, the stocking time for glass eels is around early March. For eel farms with heating conditions or a warm water supply, the stocking time for glass eels should be advanced as much as possible, as this can extend the rearing period and improve the yield and quality of eel fingerlings.

Stocking density of glass eels

Because farming methods differ, the stocking density of glass eels also varies. Generally, a stocking density of 150 g to 300 g/sq m is suitable for still-water ponds, and 500 g to 1000 g/sq m for flow-through ponds. Low-density stocking results in faster growth and a higher survival rate. Adaptation of glass eels to the environment

After long-distance transport, glass eels are in a state of fatigue, and because the temperature inside the transport container differs too greatly from the pond water temperature (especially in heated rearing ponds), an adaptation process is needed. The specific method is: place the glass eel box at the pond edge and gradually sprinkle pond water over the glass eel box; only when the body temperature of the glass eels is close to the pond water temperature (generally no more than 5°C difference) should they be put into a net cage previously placed in the pond. If transported in oxygen-filled nylon bags, first place the nylon bags together with the eels into the pond, and once the bag temperature is close to the pond water temperature, open the bags and put the glass eels into the net cage. The glass eels are generally held temporarily for 0.5 hours to 1 hour (with the aerator running); after their activity becomes normal, remove dead eels and debris, then weigh and count them separately and put them into each glass eel rearing pond.

Counting and weighing of glass eels

In order to control the stocking density of glass eels, counting must be done at stocking time to calculate the weight, size and number of individuals stocked in each primary pond. The specific method is: first gently stir the glass eels in the net cage to make them uniform, then randomly sample 2 to 4 times, weighing 50 g each time, count them using a small bowl or small spoon, and then calculate the average size. Finally, calculate the number of glass eels per kilogram, thereby obtaining the average size.

Disinfection of glass eels

Glass eels have a delicate constitution and are prone to abrasions during capture, temporary holding and transport, which can lead to infection by fungal and bacterial diseases. Therefore, disinfection must be carried out at stocking time. The disinfection method is medicated bathing; one method is medicated bathing in a container, and the other is whole-pond splashing for medicated bathing.

1. Disinfection time: container medicated bathing is carried out before the glass eels are put into the pond; whole-pond splashing disinfection is carried out in the evening of the day after the glass eels are put into the pond.

2. Disinfection drugs and concentrations: the commonly used drugs mainly include table salt and methylene blue, etc.

3. Disinfection steps and methods: when using container medicated bathing, it is generally carried out in a large water vat, so it is also called vat bathing. The specific method is: first fill the vat with 300 kg to 400 kg of clean water, then according to the proportional drug dosage, first dissolve it in a small amount of water and then pour it into the vat, and turn on the aerator to aerate, constantly stirring the water so that the medicinal liquid is evenly distributed; then weigh about 5 kg of glass eels and immerse them together with the basket in the medicinal liquid for a medicated bath of 10 minutes to 15 minutes, after which the glass eels can be taken out and stocked. Whole-pond splashing medicated bathing is carried out in the evening: dissolve the drug and directly splash it into the primary pond, turn on the aerator to stir the water so that the medicinal liquid is evenly distributed.