How to farm rainbow trout? Cage culture technology using reservoir bottom water

From January 2005 to July 2006, we conducted a small-volume cage culture trial of rainbow trout using reservoir bottom water below the Zhangwu Reservoir power station in Anyang City, Henan Province, and achieved good results. The trial is summarized as follows:

1. Materials and methods

1. Water conditions where the cages were set Zhangwu Reservoir is a hilly medium-sized reservoir with fresh water quality, abundant dissolved oxygen, pH 7.2-7.6, and average transparency of 76 cm in summer and 150-200 cm in winter. The cages were set in the backwater pool below the power station, with transparency of 150 cm, pH 7.4, dissolved oxygen 8-10 mg/L, winter water temperature 13-15°C, summer water temperature 17-19°C, and flow velocity 0.47 m/s.

2. Cage structure and setup The cages were sewn from double-layer 5×3 knot polyethylene netting. The fry cage mesh size was 0.5 cm, and the cage specification was 1 m×1 m×1 m. The adult fish cage mesh size was 2.5 cm, and the cage specification was 2 m×2 m×2 m. The four sides of the cages used bamboo as frames, foam plastic and oil drums as floats, and bricks as sinkers, so that the cages could fully stretch out in the water. The cages were placed in the water 10 days before stocking the fingerlings, so that they would soften and attach some organisms, thereby reducing abrasion when the fry and fingerlings entered the cages.

3. Fingerling stocking In March 2005, 26 kg of rainbow trout fry were purchased from Huairou, Beijing, and stocked, with a size of 4.2 g/fish. Before stocking, the fingerlings were disinfected in 3%-5% salt water for 10 minutes.

4. Feeding management

(1) Feed feeding: On the 3rd day after the fry entered the cages, rainbow trout opening feed soaked in warm water was used for feeding. The specific method was to soak the opening feed in 40°C warm water 20 minutes before feeding, with a water-to-feed ratio of 1:1. They were fed 3 times a day, respectively at 9:00-10:00 in the morning, 12:30-13:30 at noon, and 16:00-17:00 in the afternoon. When the fry grew to about 15 cm and were transferred to adult fish cages, rainbow trout adult fish feed was used for feeding, 3 times a day, at 8:00-9:00 in the morning, 12:00-13:00 at noon, and 17:00-18:00 in the afternoon, each time 7%-10% of fish body weight. A dedicated person was responsible for feeding, adhering to the "four fixed" feeding principle, and flexibly controlling the feeding amount according to weather, water temperature, and the fish's feeding situation.

(2) Daily management: A dedicated person was responsible for management, observing 24 hours a day and keeping logs. The cages were cleaned once a week to ensure water exchange inside and outside the cages. The cages were frequently checked for damage to prevent fish escape. In July, August, and September, when the weather was hottest, black plastic netting was set up above the cages to block sunlight, avoiding direct sunlight on the water surface, excessively high water temperature, and effects on feeding and growth.

(3) Fish disease prevention and control: Every half month, "bromochlorohydantoin" was splashed over the whole cage for disinfection once. The method was twice a day, 100 g each time. "Bromochlorohydantoin" was dissolved in water and evenly splashed over the whole cage, used continuously for 3 days. Antibiotic medicated feed was fed once a month, continuously for 6 days each time. The above measures had significant preventive effects. In addition, because the water temperature was low and the flow velocity was fast, no fish diseases occurred during the culture period.

2. Results

They were caught and sold in July 2006. A total of 2795 kg of rainbow trout were harvested, with an average size of 650 g/fish, a selling price of 42 yuan/kg, and an output value of 116390 yuan. Total expenditure was 66364 yuan, including 5000 yuan for fry and fingerlings, 53664 yuan for feed, 1300 yuan for fishery drugs, 5000 yuan for personnel wages, and 1400 yuan for cage depreciation. Net profit was 50026 yuan, and the input-output ratio was 1:1.75.

3. Discussion and analysis

1. Cage setup The cages were set in an area of the backwater pool with slightly slower flow velocity, slightly lower temperature, and no direct sunlight, so as to facilitate fish feeding and growth. To prevent high temperatures in summer, a sunshade shed was set up above the cages.

2. Fingerling stocking and survival rate Rainbow trout culture should stock large-size fingerlings and carry out graded rearing, that is, thinning as the fish grow, with stocking densities of 1500 fish/cubic meter for fry, 300 fish/cubic meter for fingerlings, and 60 fish/cubic meter for adult fish. In our culture process, because feed was sufficient and water quality conditions were good, the culture density was relatively large. As for the specific data on stocking density, it should depend on specific conditions. Because our culture had low water temperature, fast flow velocity, sufficient dissolved oxygen, and few diseases, the survival rate was high, reaching 86%.

3. Feed feeding and feed coefficient Rainbow trout feed aggressively and have a large food intake, so they were fed at 7%-10% of body weight. The feeding intervals should be longer. In addition, the last feeding amount accounted for 50% of the whole day. Each feeding should be stopped when the fish were 80% full, and attention should also be paid to feed palatability. When the fry were small, soaked feed was used, and later, as the fish grew, powdered feed, small pellet feed, and large pellet feed were used. Special rainbow trout feed was used, with comprehensive nutrition and fast growth.