Key Techniques for High-Efficiency Flow-Through Pond Culture of Golden Trout

The golden trout is a golden-colored strain bred in Japan from a mutant of the rainbow trout. After it was introduced into China in 1996, it was named "golden trout" based on its body color characteristics. The golden trout is a cold-water fish, with an upper limit water temperature for normal growth of 22°C and no obvious lower limit; at a lower limit water temperature approaching 0°C, it can still feed in small amounts and survive normally. Its flesh is delicious, rich in nutrients, with few bones and much meat, and high edible value; it is an excellent variety combining ornamental value, sport fishing and gourmet food, and has now become the second most important cultured species in China's trout farming industry after the rainbow trout. Golden trout can be cultured in ponds and also stocked in reservoirs, lakes and rivers; especially when cultured in flow-through ponds, it can grow all year round, with a yield per mu as high as 10,000 kg to 20,000 kg, giving extremely high economic returns. The high-efficiency flow-through pond culture techniques for golden trout are introduced as follows:
　　
I. Pond construction. Mountain streams, spring water, groundwater, reservoir bottom drainage, etc. can all serve as water supply sources for flow-through pond culture of golden trout. Such water sources generally have a water temperature above 0°C in winter and above 22°C in summer, with dissolved oxygen above 6 mg/L and pH between 6.5 and 8, meeting the water quality standards for golden trout culture. Pond construction should be premised on no seepage and unobstructed water flow. The terrain should have a certain slope to facilitate water intake and drainage, while the drop of the water helps natural aeration. Each pond generally has an area of 100 sq m to 200 sq m, with a concrete structure and a rectangular shape, which is favorable for feeding, management and control of fish diseases, and allows the water source to flow evenly to all parts of the pond. There are two forms of pond inlet and outlet: one is equal to the width of the pond, with a gate from top to bottom so that the entire cross-section keeps passing water; this form is suitable for fish farms with large water volumes. The other is an inlet width of only about 1/5 of the pond width, with an outlet width of 1/2 of the pond width. At the same time, to prevent wild trash fish from entering the pond and pond fish from escaping, fish screens must be installed at the inlet and outlet. Trout ponds can be arranged in parallel or in series, but the series arrangement is better, as it is convenient to manage and saves labor.
　　
II. Fingerling stocking. Fingerlings should be uniform in size, agile in swimming, robust in constitution, and bright golden yellow in body color. The stocking density of fingerlings is restricted by factors such as water volume, water temperature and dissolved oxygen status in the water; within the range permitted by rearing conditions, the stocking amount of fingerlings is directly proportional to the yield of market-size fish. The stocking size is determined by the culture duration, water temperature and the planned market size, generally 80 g to 100 g per fish. Practice has proved that with a water supply of 40 L to 300 L per second (the higher the temperature, the greater the water supply), 150 to 200 golden trout fingerlings can be stocked per sq m (the larger the size, the lower the stocking density). Before stocking, the pond should be fully sun-dried and thoroughly disinfected with quicklime or bleaching powder; fingerlings should be disinfected with a 2% to 3% salt solution before stocking, and it is best to avoid stocking at midday when temperatures are high.
　　
III. Feed feeding. In the early stage of fingerling stocking, wild trash fish and livestock and poultry liver can be ground 2 to 3 times with a meat grinder into a paste, spread on a fine wire tray and hung in the water, with a daily feeding amount of 6% to 8% of fish body weight, fed 3 times a day; afterward, artificial feed is gradually used, with the feed ratio: plant and animal feed each accounting for 50%. Animal feed includes fish meal, meat meal, small trash fish, silkworm pupae and livestock and poultry viscera, etc., while plant feed includes cake meal, bran, rice bran, vegetable leaves, etc. The pellet size should be suitable for swallowing, generally 4 mm to 6 mm in diameter. Feed twice a day by hand scattering, with a feeding amount of 2% to 3% of the total fish weight. This can be flexibly adjusted according to weather, water temperature and the fish's appetite; do not feed too much, so as to avoid polluting the water quality.
　　
IV. Daily management. The water used for golden trout culture must be clean and free of pollution. The pond bottom and walls should be cleaned and brushed regularly; it is best to install a fish screen 2 m to 3 m from the drainage outlet so that debris can settle there and then be removed with a suction pipe, reducing pollution to the downstream ponds. To achieve high yield of golden trout, management should first maintain sufficient water volume and full dissolved oxygen content; for this purpose, aeration equipment should be added to the fish pond, and once oxygen is insufficient, it should be replenished immediately. Second, market-size fish that have reached the edible standard (over 200 g per fish) should often be caught and sold promptly, and individuals showing obvious differences in growth should be selected and raised in separate ponds.
　　
V. Disease prevention and control. Common diseases in flow-through pond culture of golden trout are, first, vibriosis, which mostly occurs in late spring and autumn. In the early stage of the disease, the body surface and the base of the fins gradually turn black; in severe cases, the epidermis ulcerates and necrotic muscle is exposed. Prevention and control: feed 75 mg to 100 mg of sulfonamide drugs per kg of fish body weight, fully mixed with feed, for 5 to 7 consecutive days. Second, hepatic lipidosis, which is caused by incomplete nutritional content or moldy and deteriorated feed. Diseased fish have a blackened body color, enlarged liver, float alone in slow-flowing areas, and are inactive. Prevention and control: once diseased fish are found, immediately switch to high-quality feed, reduce the feeding amount, and increase the vitamin content in the feed. Fish with milder disease can fully recover after about 30 days, while those with severe disease cannot be saved.