Detailed Explanation of Large Yellow Croaker Fingerling Cage Culture Techniques

I. Cage Setup

1. Selection of Sea Area The water flow velocity in the sea area is generally within 1 m/s, and the flow direction is straight and stable; avoid setting up in sea areas with eddy currents. At low tide, the bottom of the cage should be at least 1.5 m above the seabed. Throughout the year, the surface water temperature in the sea area ranges from 7-30°C, salinity from 12-32, and transparency from 0.2-3.0 m.

2. Selection of Cage Specifications Currently, the cages used for cultivating large yellow croaker fingerlings are all floating cages, that is, the cages are hung on a wooden frame with 10 frame positions of 5 m × 5 m. For fingerlings of 4-5 cm, knotless netting with a mesh length of 5-8 mm is generally used; for fingerlings over 5 cm, knotless netting with a mesh length of 10 mm is used.

3. Cage Setup The cage frame is fixed with 3000-5000 denier polyethylene cables along the direction of the tidal current using stakes. There are two ways to suspend the cage on the frame: one is in slow-current sea areas, where the cage is hung directly inside the frame, and then the four corners of the cage are stretched downward with sandbags, called a "soft cage"; the other is in rapid-current sea areas, where the four corners of the cage are stretched and hung on a hexahedral frame welded from galvanized pipes, called a "hard cage." This type of cage can both block the current and maintain the shape of the cage, avoiding fingerlings being scraped by the netting.

II. Fingerling Stocking

1. Fingerling Transportation Currently, there are mainly three ways to transport large yellow croaker fingerlings: first, transport in oxygen-filled plastic bags, requiring fingerling specifications below 2.5 cm and maintaining a low-temperature state; second, transport by live-fish boat, requiring fingerling specifications above 3 cm; third, transport in ordinary ship cabins with continuous aeration. Feeding should be stopped before transportation, and the fingerlings are required to be uniform in size, robust in constitution, and good in vitality.

2. Fingerling Stocking The time for putting fingerlings into the cage should be chosen during neap tide periods, preferably at the moment of slack tide when the current is slow. In winter and spring when temperatures are low, choose sunny afternoons; in high-temperature seasons, it is advisable to choose cool mornings and evenings. Fingerlings of different specifications should be placed in cages with different mesh sizes, and fingerlings of uniform size should be stocked in the same cage to prevent cannibalism. Generally speaking, the stocking density for fingerlings of 3 cm specification is about 1000 individuals/cubic meter.

III. Fingerling Feeding

1. Feed Types The large yellow croaker is a carnivorous fish. Newly caged fingerlings can be fed suitable-sized minced fish and shellfish meat or artificial compound feed. Fingerlings over 25 g can be directly fed chopped fish meat pieces.

2. Feeding Time Intervals Since the large yellow croaker has characteristics of slow feeding and small amounts, the method of small amounts and frequent feeding with slow feeding should be adhered to during the cultivation process. For fingerlings within 30 mm in size, feed 6-8 times per day when first caged, and gradually reduce the frequency depending on their growth. Since fingerlings feed better in the morning and evening periods, the feeding time intervals can be appropriately shortened. At noon when sunlight is strong, fingerlings generally do not float up to feed, so the feeding time can be appropriately extended.

3. Feeding Methods Feeding should be at fixed points, and first use the hand to stir the water so that the fingerlings develop the habit of gathering in schools and floating up to feed. First feed quickly at the gathering spot, and after a large number of fingerlings have eaten their fill and dispersed or sunk, continue feeding small amounts around the area so that weaker fingerlings can also get feed. Sometimes due to environmental and climate changes, fingerlings only feed in the middle layer. The feeding amount should be controlled based on previous feeding conditions and the "clucking" sound made by fingerlings when feeding. If the water current is too rapid, it is not suitable to feed.

IV. Daily Management

1. Cages During the Fingerling Cultivation Stage Due to the small mesh size, after a period of cultivation, attachments will grow on the netting, causing mesh blockage. Especially in high-temperature seasons, if screen netting with mesh below 40 mesh is used, it is very easily blocked by attachments, causing fingerlings in the cage to die from lack of oxygen. Therefore, the mesh blockage situation should be checked frequently, and the netting should be replaced and cleaned in a timely manner. Generally, in high-temperature seasons, netting with mesh below 5 mm should be replaced and cleaned at every neap tide, and size inspection and screening of the fry should be conducted. To prevent fish body injury and eliminate pathogens, formalin can be used for fish body disinfection during cage changing. If fingerlings are found to have decreased vitality, are satiated, or the water current is rapid, then cage changing operations should not be carried out.

2. When the Water Current Is Rapid Pay attention to observing the reduction in cage capacity and the growth dynamics of fingerlings, and check whether the cage ropes are broken and whether the sinkers have shifted. If no special reason is found for fingerlings not floating up to gather and feed, and the unique "clucking" sound of the large yellow croaker cannot be heard, then consideration should be given to whether the cage is damaged and fish have escaped or disease has occurred, and measures should be taken promptly. If there are many seabirds in the sea area, a net cover should be placed over the cage.

3. Daily regular observation should be conducted on environmental factors such as water temperature, specific gravity, transparency, and water flow, and close attention should be paid to the schooling, feeding, diseases, and mortality of fingerlings. Detailed production records and medication logs should be kept, and the causes of seasonal disease outbreaks should be summarized and corresponding measures taken.