Detailed Explanation of Key Points of Sturgeon Cage Culture Technology

Recently, sturgeon farming in South China has shown a trend of gradual recovery and warming, especially in Hainan Province, China, where a large number of shrimp farmers have switched to sturgeon farming. Sturgeon farming models are diverse, and here we introduce a rapid grow-out technology for sturgeon in cages. Using cages to farm sturgeon has many advantages: first, feeding management is convenient; second, no specially made fishing nets are needed at harvest, and the fish can be harvested all at once or in stages as needed for sale, which facilitates live fish transport and storage and helps with market regulation; third, it can adapt to mechanized operations and the development of modern farming technology. The rapid grow-out technology for sturgeon in cages is introduced as follows:

1. Cage setup. Rapid grow-out cages for sturgeon are generally woven from polyethylene thread, with specifications of 40 m×4 m×2.5 m. The mesh size depends on the size of the sturgeon fingerlings stocked, following the principles of not letting fish escape, facilitating water exchange, and preventing food from leaking through the bottom net panel. If sturgeon fingerlings of more than 100 g each are stocked, the mesh size should be 2-3 cm. Because feeding is frequent, an open-top cage is preferable, and the setup method should be a floating frame type. Cage placement should be chosen in places with good water quality and a water depth of more than 3 m, and should also have conditions such as slight water flow, shelter from wind, exposure to sunlight, and a broad water surface. In large reservoirs, cages should be set up in suitable places in the reservoir bay; in small reservoirs, cages should be set up in waters not far from the dam.

2. Fingerling stocking. The most suitable water temperature for sturgeon growth is 20-25 degrees C, and the suitable stocking time is late May to early June. The larger the fingerlings stocked, the better, generally 100-200 g per fish, with a stocking density of 35-40 fish per sq m. Stocking should be carried out at 6-8 o'clock in the morning, when the temperature difference between the fingerling water and the reservoir water is relatively small.

3. Feed feeding. Rapid grow-out of sturgeon in cages mainly involves feeding fresh animal bait and artificial compound feed. The compound feed has a protein content of 40%-45%, and the main raw materials include fish meal, silkworm pupae, meat and bone meal, casing meal, blood meal, yeast, oil cake, wheat, corn, and so on. Its reference formula (%): fish meal 37, silkworm pupae 15, blood meal 15, yeast 4.5, oil cake 5, wheat 17, corn 4, additive premix 2, binder 0.5. Weigh the materials according to the formula, crush them, process them into pellets of 2-3 mm particle size, dry them, and store them for use. Two points must be emphasized here: first, all raw materials should be crushed very finely, preferably to a fineness of more than 40 mesh; second, the stability of the pellet feed in water should be such that it can remain intact for 1.5-2 hours, which means a binder with good performance must be used. Of course, if conditions permit, commercial feed can also be chosen.

After the fingerlings enter the cage, stop feeding for 1-2 days so they can adapt to the cage environment. Two days later, feed a small amount of compound feed multiple times on feeding platforms set around the cage (each cage can use 4-6 bamboo sieves of 0.3-0.4 sq m, 0.2 m deep, suspended near the bottom of the cage body) to induce the fish to feed, feeding 5-6 times a day, so that after 7 days the fingerlings can become fond of eating artificial compound pellet feed. Then enter the normal feeding stage, feeding twice each in the morning and afternoon every day, with the daily feeding amount generally 4%-5% of the fish body weight in the cage. Sturgeon have the habit of foraging at night, so the feeding amount in the afternoon should be appropriately larger. How can the appropriate feeding amount be determined? First, calculate the daily feed amount based on the daily feeding rate; second, check whether there is leftover food and how much; third, carefully observe the changes in the shadows of the fish school in the “second layer of water” below the feeding point during feeding. Usually, at the beginning of feeding, the fish school gathers densely to compete for food, the shadow is large, and there is rolling in the cage. After the peak of feeding, the fish school shadow becomes smaller or disappears, and the water surface tends to become calm. At this point, feeding should end.

4. Management measures. Cages must be guarded by dedicated personnel, and inspections must be carried out multiple times every morning, noon, and evening to observe fish conditions and water conditions. In particular, it is necessary to prevent floods from washing away the cages, prevent the cages from being stranded when water recedes, prevent enemies from damaging the cages, and prevent mud and debris from pressing down and sinking the cages. In addition, the cages should be cleaned about once every 10 days, especially immediately after floods, to remove debris and excessive attached algae and keep water exchange inside and outside the cages unobstructed.

5. Fish disease prevention and control. Sturgeon have bony plates on their bodies, have few natural enemies, and have a short history of artificial farming, so epidemic and explosive diseases are not yet common. Existing reports are mostly caused by deterioration of water quality, but disease prevention work should still be done well by focusing on water quality regulation and adhering to prevention first. Specific practices: before the cage is put into the water, soak and treat it with quicklime water or bleaching powder, and put it into the water 7-10 days in advance to let algae attach, so as to avoid damage to the body surface skin after the fingerlings enter the cage; disinfect the fingerlings before they enter the cage by soaking them in 3%-4% salt water for 15-20 minutes; normally, dead or injured fish should be removed as soon as they are seen to prevent pollution and cross-infection; every 15-20 days, use 2-3 kg of quicklime per cage, dissolve it in water, and splash it on the cage body and nearby waters, once a day for 3 consecutive days; every day, leftover bait must be removed, and the feeding platforms must be scrubbed and dried in the sun. The area around the feeding platforms should be regularly splashed with quicklime water for disinfection, so as to enhance sturgeon feeding and reduce the occurrence of fish diseases. During the rearing period, if trichodiniasis, costiasis, and chilodonelliasis occur, they can be controlled with potassium permanganate at 2 mg/L or copper sulfate at 75 mg/L.