Key Technical Points and Detailed Daily Management Methods for Rainbow Trout Farming

1. Rearing management of adult fish. Adult fish ponds can be earthen ponds or cement ponds. Earthen ponds are preferably about 1 mu, with a water depth of 1.5 m; cement ponds are preferably about 50 sq m, with a water depth of about 1 m. The pond bottom should preferably have a drainage outlet to facilitate regular discharge of feces or waste feed. The mesh of the escape-prevention screen at the outlet is preferably 1×1 cm; if too large, fish will escape, and if too small, it is easily clogged by leaves and moss. Before stocking, the pond must be cleared with lime. The fingerlings stocked should be screened, uniform in size, and preferably about 50 g per fish. Reasonable dense stocking should be carried out according to water flow and dissolved oxygen conditions. Generally, 1-1.5 kg (about 3 lb) of rainbow trout can be raised per liter.
In rearing management, the three tasks of water, feed, and disease should be given priority. The water quality must be continuously renewed, generally more than once per hour, and the pond must also be brushed and cleaned regularly, generally once a month.
For ponds with relatively high density or relatively small water flow, aeration equipment should be installed, and the pond should be brushed frequently, generally once every half month. Adult fish feed generally consists of 30%-40% animal components and 70%-60% plant components. The feed must be fresh. For pelleted feed, the protein content is preferably 40%-42%, the fat content is preferably 7%-9%, and the carbohydrate content is preferably 9%-12%. The daily feeding amount is 3%-5% of fish body weight, fed twice a day. During the adult fish rearing stage, rainbow trout are prone to liver disease and enteritis, with a very high mortality rate, so disease prevention work should be done carefully.
The growth cycle for raising rainbow trout to marketable fish is generally 1 year and 6 months to 1 year and 10 months. The marketable size is over 300 g.
2. Site construction conditions. First, the water source and site must be well chosen. The water source can be cold spring water, bottom water of reservoirs, groundwater, etc., but the water temperature must remain at 7-20°C year-round. The water volume must be abundant, with small seasonal variation, and the flow rate must be constant throughout the year. Where the annual variation is obvious, the water flow rate during the dry season should be used as the basis for planning. About 100 liters per second of water can produce 20 tons of fish. The dissolved oxygen content of the water source should be above 5 mg/L. The water quality of the water source should also be carefully investigated. Calcium-rich water has abundant natural feed, and relatively fresh water quality can be used; swamp water and peat water that are acidic should be abandoned. It is necessary to investigate whether waste discharged from nearby factories, mines, etc. pollutes the water source. After water quality analysis, test the water with several dozen fingerlings. When selecting a site, consider whether the soil quality is suitable. Sandy gravel bottoms, black soil, and loess bottoms are all acceptable. The terrain should have a certain slope, generally 1-3:1000, to facilitate the construction of series-connected ponds, with natural drop, water cascade for aeration, and easy discharge of waste. The water source should be higher than the pond water surface, so that gravity flow can be used, eliminating mechanical pumping, saving electricity, and reducing expenses.
Site construction must also consider whether there is a power source nearby, to facilitate the installation of power lines and lighting lines, so as to mechanize feed processing and install aerators, etc. In addition, it is also necessary to consider whether there is a nearby feed source, transportation conditions, and commercial conditions.
Prevention and treatment of common fish diseases:
1. Common fish diseases during the incubation period. The main one is saprolegniasis, which directly affects the hatching rate. The hyphae of Saprolegnia not only infect dead eggs but also surround good eggs.
Prevention and treatment methods: (1) Pick out dead eggs in time. (2) Place the eggs in a 1/200,000-1/300,000 malachite green solution and soak for 30-60 minutes. (3) Place the eggs in a 1/3,000-1/5,000 formalin solution and soak for 3 minutes. (4) Disinfect the eggs with salt water at a concentration of 10.5%-11%; at the same time, good and bad eggs can be separated.
2. Common fish diseases during the fry and fingerling stage.
(1) Ichthyophthirius. Symptoms: parasitizes the subcutaneous tissue of the body surface, gills, and fins. Many small white spots can be seen on the body surface and gills, making the fish restless and causing difficulty breathing. Prevention and treatment methods: use malachite green at a concentration of 0.3-0.4 ppm, stop the water for 90 minutes for disinfection; in severe cases, 0.5 ppm can be used for 60 minutes. Each treatment course is 2-3 days.
(2) Gyrodactylus. Symptoms: parasitizes the gills, mouth, head, and body surface of the fish, destroys epidermal tissue, making the fish restless and causing poor appetite; in severe cases, death occurs. Prevention and treatment methods: when the water temperature is above 15°C, use formalin at a concentration of 1/1,000-1/5,000 and soak for 30 minutes; when the water temperature is below 15°C, use a concentration of 1/2,000-1/3,000 and wash for 30 minutes.
(3) Enteritis. Symptoms: intestinal congestion and inflammation, no food, and in severe cases the intestines are filled with pus. Prevention and treatment methods: keep feeding utensils and feed-processing machinery clean, disinfect regularly, and do not feed spoiled bait. Therefore, good preservation work for the bait must be done. Add 3%-5% garlic to the feed and feed continuously for 3-6 days. Add 500 mg furazolidone per 50 kg of feed and feed continuously for 3-6 days.
(4) Trichodina. Symptoms: parasitizes the skin and gills of the fish; diseased fish have reduced appetite and difficulty breathing. Prevention and treatment methods: soak and wash with copper sulfate or ferrous sulfate at a concentration of 4 ppm (ratio of the two is 5:2) for 20-30 minutes. Soak and wash with malachite green at a concentration of 0.3-0.4 ppm, once every other day for a total of 3 times.
3. Common fish diseases during the adult fish and broodstock stage.
(1) Argulus. Symptoms: parasitizes the body surface, sucks fish blood, punctures and irritates the fish skin, causing wounds. Prevention and treatment methods: sprinkle 6% wettable benzene hexachloride powder throughout the pond at a concentration of 1 ppm. Use refined trichlorfon 96% at a concentration of 1.5 ppm, wash for 3-4 hours, then move into a new pond.
(2) Fatty liver lesions. Liver disease is one of the main diseases of rainbow trout, and it is very harmful. It is mainly caused by nutritional deficiency in the feed or feed spoilage. Once it occurs, it can cause mass mortality. Diseased fish have darkened body color, pale gills, anemia, and yellow fluid flowing from the anus. When dissected, the internal organs mostly contain yellow mucus, and the liver is earth-yellow. Prevention and treatment: because this disease is caused by long-term improper nutrition, it must be addressed by improving nutritional conditions. Take care not to feed spoiled feed containing oxidized fat, and promptly feed fresh feed when fish disease is discovered.