Detailed Explanation of Cage Culture Techniques for Yellow Catfish in River Channels

The Xinjiang River is the third largest river in Jiangxi Province, with rich fishery resources, relatively good water quality, and light pollution. Water transparency ranges from 0.7 to 2 m. The Yingtan section has a total length of 104.05 km. Fanjia Beach in Jinjiang is located in the lower reaches of the Xinjiang River (Yingtan section), where the water is relatively shallow. Fanjia Beach has a total length of 2 km, with the deepest point at 3.6 m and the shallowest at 0.5 m. In 1999, we selected the deep area of Fanjia Beach to carry out cage culture experiments on yellow catfish. Fish fingerlings were stocked into cages on March 22 of that year and harvesting began on December 20. After nearly 9 months (273 days) of rearing, a total of 22,538 kg of fresh fish was harvested, with an average yield of 45.08 kg/sq m.
　　
1 Main Techniques and Measures:
1.1 Cages and Fingerlings. Double-layer closed polyethylene cages were used, with specifications of 5×5×2 (m3) and inner and outer mesh sizes of 3 cm and 4 cm respectively. To prevent feed loss, the outer layer of the cages was fitted with frames, each cage connected with 4 bamboo poles, using old gasoline drums as floats and iron anchors and bricks as sinkers. The cages were arranged in a single-line two-wing formation, with a row spacing of 6 m and a cage spacing of 1.5 m. There were 20 cages in total, totaling 500 sq m. The cages were placed in the water 10 days before fingerling stocking. After some fouling organisms had attached to the cages, fish were stocked starting on March 22, with a stocking weight of 2,807.9 kg, a total of 50,529 fish, an average weight of 55.57 g per fish, and an average stocking density of 101.0 fish/sq m. When fingerlings were stocked into the cages, they were disinfected by soaking in 12 mg/L potassium permanganate or 3% saline solution.
1.2 Feed and Feeding. Pellets produced by Yingtan Liangmao Feed Company using a Beijing Agricultural University formula were used, with crude protein 27%-30%, crude fiber ≤12%, calcium 0.5%-1.3%, phosphorus ≥0.06%, sodium chloride 0.2%-1%, and moisture ≤11%.
A small iron spoon was used to broadcast the feed. A 5-day feeding training was conducted first, so that the yellow catfish formed a conditioned reflex and would race to the surface of the cage to compete for food as soon as they heard the sound of knocking on the boat. Feeding adhered to fixed times and fixed amounts, 2-3 times per day, and three times per day from July to September. The times were generally 7-8 AM, 11 AM-12 PM, and 4-5 PM. Feeding followed the principle of going from less and slow to more and fast, then back to less. When only a very small number of fish were still slowly feeding at the cage surface, feeding was stopped. The feeding amount was generally about 3% of body weight, and the feeding amount was changed once every 20 days.
1.3 Management
1.3.1 Fish Disease Prevention and Treatment. Throughout the entire culture process, we consistently adhered to the principle of “prevention first, prevention more important than treatment,” and promptly diagnosed and treated any abnormal conditions. When fingerlings were stocked into cages, they were disinfected by soaking in 12 mg/L potassium permanganate or 3% saline solution for 10-15 minutes. About one month after stocking, attention was paid to preventing saprolegniasis. For each cage, 50 g of “Shuimeijing” produced in Chengdu was dissolved in water and splashed, twice a day for two consecutive days. Normally, medicated bags were hung routinely, with 50 g/bag of “Jingshuiwang” and strong chlorinated disinfectant hung at opposite corners of the surface layer of each cage to prevent disease. During the peak growth season of the fish, 60 mg/L quicklime water was splashed twice a month.
1.3.2 Flood Control and Escape Prevention. Flood control and escape prevention in river channel cage fish culture is a key issue. Normally the water level is relatively stable. During flood season, attention was paid to inspecting and reinforcing the cages and moving them to wind-sheltered areas with slow current. Regular cage patrols were conducted to remove foreign matter. In addition, two barrier nets were set up in the culture area, on the one hand to block debris floating down from upstream, and on the other hand to prevent ferocious fish from breaking through the cages and causing fish to escape.
2 Culture Results
2.1 Yield. From stocking to harvest, yellow catfish were reared for 273 days, and a total of 44,454 fresh fish were harvested, totaling 22,538 kg, of which the largest individual was 1,600 g and the smallest was 270 g. The average individual weight of yellow catfish reached 507 g, the average yield reached 45.08 kg/sq m, and the survival rate was 88%.
　　
2.2 Economic Benefits. The river channel cage culture experiment on yellow catfish stocked 20 cages in total and produced 22,538 kg of fish, achieving a total output value of 360,600 yuan. The total cost was 133,100 yuan, mainly including fingerling costs accounting for 37.56%, feed costs accounting for 58.68%, and medicines, labor, etc. accounting for 3.76%. The total profit was 227,500 yuan, the output value per unit area was 721.2 yuan/sq m, and the input-output ratio was 1:2.71.
3 Experience
3.1 Flood Control and Escape Prevention
Flood control: First, site selection must be done well. Sites should be chosen in eddy bays and other wind-sheltered areas with relatively low flow velocity, with water depth of 3-6 m. Second, when flood season arrives, cages should be inspected and reinforced. The safest way to avoid floods is to sell fresh fish that can be marketed before the flood, transfer those that cannot be marketed to ponds or reservoirs inside the polder for temporary holding, and move them back to the river channel for culture after the flood.
Escape prevention: It is necessary to be familiar with the hydrological conditions of the river channel and the distribution of ferocious fish, promptly block and remove debris washed down from upstream, and set up 1-2 barrier nets on the outer edge of the culture area, using two-layer cages and metal cages.
3.2 Disease Prevention. During the entire experiment, except for one outbreak of saprolegniasis in late April, no serious diseases occurred at other times. The survival rate reached 88%. To reduce disease outbreaks in river channel cage fish culture, the following three critical points should be well controlled: (1) Fingerling stocking point. When fingerlings are stocked into cages, potassium permanganate, saline solution, malachite green, etc. should be used to disinfect the fish body. (2) Low-temperature point. Shortly after fingerlings are stocked into cages, there is an adaptation process. Fish swim around in the cages and are prone to abrasions and infection. At this time, drugs such as malachite green or Shuimeijing should be frequently splashed. (3) High-temperature point. In the peak disease season of August to September, quicklime should be frequently splashed and medicated bags should be hung in the cages for disinfection.
3.3 Fingerlings and Feed. Fingerling size should generally be relatively large, preferably 6-18 fish/kg. Fingerlings should be sourced locally to avoid long-distance transport causing reduced resistance and affecting survival rate. Stocking density should be flexibly controlled according to cage specifications, the fish's own growth characteristics, market size, technical management level, input conditions, etc. To achieve better benefits, the method of raising two batches of marketable fish per year can be adopted, that is, stocking two sizes of fingerlings, 6 fish/kg and 16-20 fish/kg, around the Spring Festival. Around the Dragon Boat Festival, some fish can be marketed. After that, they are divided among cages and management is intensified. By around the Mid-Autumn Festival, all can be harvested and marketed. Around the Dragon Boat Festival and Mid-Autumn Festival, market fish supplies are generally in demand and prices are firm. In addition, fish raised in river channel cages have better body color and taste, giving them strong market competitiveness.
In river channel cage fish culture, to reduce feed loss, a feeding frame can be used for extruded feed, and for hard pellet feed, a feeding platform can also be set up 30-50 cm below the water surface. When feeding, the method of going from less and slow to more and fast, then back to less should be followed.