(1) Artificial seedlings are best reared in conditions with an optimal salinity of 32 to 35, a temperature range of 19 to 24°C, dissolved oxygen levels of 0.0005%, and a stocking density between 50 to 250 tails per liter. Slightly larger aquaculture systems can help improve survival rates at lower densities, although this requires more feeding. To prevent light reflection and direct sunlight, cement tanks or non-reflective black polyethylene containers are commonly used.
The rearing tanks should be prepared a few days before the fish hatch. The water is filled into each tank, and seawater must be sterilized and filtered before use. It's essential to maintain a salinity of 32 to 35 and a water temperature of 20 to 22°C before introducing the fry. Prior to placing the fish in the tanks, green algae or other phytoplankton species are inoculated to provide food for the rotifers, with green algae being the preferred choice.
After approximately 60 hours, the eggs fully hatch, and the newly hatched fish are transferred to the culture pool using a siphon tube. Before siphoning, the circulating water is stopped. At this point, the fry float on the surface, while the egg membranes and unhatched eggs sink. Care must be taken during the process to avoid transferring these unwanted materials along with the larvae.
Newly hatched fry measure about 2.2 to 3.5 mm in length. They have oil globules in the posterior part of the yolk sac and possess 24 sarcomeres. The anterior part of their body is bent over the yolk sac, and they begin feeding 3 to 5 days after hatching. Larval diets include oyster eggs, diatoms, green algae, copepods, Artemia, and other suitable feeds. Different types of food should be provided at different developmental stages, as outlined below:
Days after hatching | Type of bait
3–13: Oyster eggs
5–18: Rotifers
10–14: Copepods
16–40: Artemia nauplii
29–41: Cooked protein, rice bran, flour, etc.
When starting artificial cultivation, the water and air temperatures should be kept between 20–22°C, and the salinity should be maintained at 32‰–35‰. Water is supplied via a water tower and undergoes filtration and UV sterilization. On day four after hatching, the water in the rearing tank is diluted with fresh water, reducing the salinity by 0.5‰ daily. By day seven, the salinity should drop to 30‰, and gradually decrease to 20‰ by day 30. Throughout this period, daily monitoring of water temperature, salinity, dissolved oxygen, and pH is crucial. Additionally, nitrate, ammonia nitrogen, sulfide, and phosphate levels should be measured regularly.
The acceptable limits for fry include up to 3.00 micrograms of nitrite, 90 micrograms of nitrate, 30 micrograms of ammonia, 9 micrograms of phosphate, and 5 micrograms of hydrogen sulfide. Dissolved oxygen must remain above 0.0007% on the first day, with a pH between 7.9 and 8.3. Each day, the rearing tank is cleaned using a small siphon to remove dead seedlings and leftover feed. In recirculating systems, debris tends to accumulate in the center, making it easier to remove through siphoning. Between 30 and 50 days, the fry grow rapidly and can be fed wet synthetic feeds, older Artemia, and large copepods.
For the first 40 days, do not move or catch the eel fry, as this can result in total mortality. If movement is necessary, it should be done only after 50 days of hatching.
(b) Carp seedlings are typically captured from the sea and temporarily conserved before domestication, or artificial seedlings can be transferred to fingerling ponds after more than 50 days of growth. The area of carp fingerling ponds should range from 0.07 to 0.15 hectares, with a water depth of 1.5 to 2 meters. The pond bottom should not contain excessive silt, and the water should maintain a certain level of salinity. Before stocking, the pond should be cleaned thoroughly.
Each hectare can hold 45,000 to 60,000 3 cm fry. After stocking, feed is provided twice daily, combining barley and bean cake, which can be ground into a dry powder to aid feeding. Once the fry are all in the pond, fertilization begins to cultivate zooplankton, gradually increasing the fertilizer amount. After about one month of feeding, the eel fry can grow to 5–7 cm and then be moved to adult ponds for further development.
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