Matters needing attention in cage culture of rainbow trout

Rainbow trout (scientific name: Oncorhynchus mykiss) is a kind of fish of Salmonidae and Pacific Salmon, cold-water fish of Salmonidae, and a precious species in pond culture. Native to northern North America and the west coast of the Pacific Ocean, it mainly lives in low-temperature fresh water and has higher requirements for the quality of aquaculture waters. There is also a species called "hard-headed trout" that lives in fresh water or seawater in different seasons. Rainbow trout is a food fish that has been moved to many countries but has become an invasive species in some areas. The food is raised in the reservoir, weighing about 3 kilograms, and the roasted rainbow trout is delicious.

Rainbow trout like to live in clear waters with low water temperature, high dissolved oxygen and abundant flow. the limit temperature of rainbow trout is 0-30 ℃, the suitable life temperature is 12-18 ℃, and the optimum growth temperature is 16-18 ℃. When it is lower than 7 ℃ or higher than 20 ℃, its appetite decreases, growth slows down, feeding stops when it exceeds 24 ℃, and then gradually weakens and dies. It has a high demand for dissolved oxygen in water. The lethal point was less than 3 mg / L of dissolved oxygen, and the "floating head" began to die when the dissolved oxygen was less than 4.3 mg / L. When the dissolved oxygen is less than 5 mg / L, the respiratory rate increases.

Rainbow trout culture needs to pay attention to:

I. selection of aquaculture waters

Rainbow trout like to live in an environment with clear water quality, unobstructed water flow and sufficient water quantity, and like countercurrent and high dissolved oxygen. Therefore, when choosing waters for cage culture, we should pay attention to the open water surface of large and medium-sized reservoirs with sufficient water source, clear water quality, no pollution, little annual change of water level and annual variation of water temperature between 4 ℃ ~ 24 ℃. The water quality meets the standard of fishery water. Water velocity 10cm/s~30cm/s, proper control of water flow stimulation can cause the normal movement of rainbow trout, thus increasing feeding and accelerating growth; when the transparency of water body is more than 2.0m, the higher the transparency of water body is, the lower the degree of eutrophication is, and the better the water quality is, the better the production performance of cage fish culture is, the higher the potential fish yield is. The annual average lowest value of dissolved oxygen ≥ 6mg/L, when dissolved oxygen is lower than 5mg/L, rainbow trout respiration rate increases, feel uncomfortable, below 4mg/L will die, above 6mg/L normal growth, 9mg/L growth rate is the fastest.

Second, the structure and setting of the cage

1. The shape of the cage and the shape of the material cage had better be rectangular. The rectangular cage is placed in the water body perpendicular to the flow direction, and the water exchange is fast and the exchange capacity is large, which can ensure the fresh water needed for rainbow trout culture. The material for making the cage is strong and durable, enough to bear the weight of the fish in the cage, does not hinder the exchange of water bodies, is corrosion-resistant, lightweight, does not damage the fish, and the price is reasonable. The size of the cage can be made according to the requirements of different periods of rainbow trout culture, because the daily management of rainbow trout culture is more complex, in order to facilitate operation and management, it is best to use floating framework operation platform. Floating frame operating platform requires strong material, durability, good buoyancy, resistance to wind and waves, easy to operate, easy to maintain, steel and foam composed of the frame platform is more reasonable, but also the most common. Hanging the box hook on the frame platform is an independent rainbow trout cage. The cage is best made of nylon mesh, which has the advantages of firm and strong, fine and small knots, low resistance during water exchange, corrosion resistance, light and not easy to scratch the fish. The cage cover should be able to completely cover the top of the cage and be movable. first, it can prevent the invasion and predation of carnivorous fish and prevent natural enemies and thieves; second, it can block light and reduce the stress response of rainbow trout to light. at the same time, reducing the time of rainbow trout exposure to sunlight helps to enhance the disease resistance of rainbow trout immune system, thus improving production performance. Third, due to reduce the entry of light and inhibit the growth of biological fouling, reduce the attachment of the cage wall, which is conducive to water exchange.

two。 Cages should be set in open waters to avoid narrow bays, lake branches and stagnant areas, as well as areas where the current is too fast and the waves are too strong. Because of the narrow reservoir bay and stagnant water area, the water exchange in the cage is insufficient, and the water quality in the cage becomes worse, which may cause the physiological stress reaction of fish; if the current is too fast and the wind and waves are too big, the water exchange is too frequent, and the top water of fish swims and consumes physical energy. it will cause the physical stress reaction of fish, and the cage is easy to be damaged. The water level change of the cage culture area should be able to predict that the lowest water depth of the cage should be at least 5m deeper than the bottom of the box, and there should be no weeds or too many rocks in the area where the cage is set up. For ease of management and safety, cages should be located in areas where staff can easily reach and are often observed.

3. The arrangement of cages had better be arranged in the word "one", placed perpendicular to the current, must not be arranged as a "chessboard", and the flow of water should not be allowed to flow directly from one cage to another. Taking into account the change of water level and the effect of wind and waves, each cage is connected with adjacent cages by wire clasps, and the peripheral four corners of each row of cages are fixed with anchor wire rope to prevent them from being blown away by wind and waves or deviating from the culture area due to the change of water level.

III. Stocking of rainbow trout

1. The weight of rainbow trout fingerling in the quality cage had better be more than 50g, and the specification is relatively uniform, without injury or disease. The main signs of healthy fish species are: the whole school has uniform body color, no scars, no broken fins, and is not easy to catch.

two。 The amount of fish released depends on the expected total weight and average individual weight of rainbow trout in the cage at harvest, as well as the optimal fish carrying capacity of the cage. The optimal fish carrying capacity of the cage varies with the change of the quality of the culture environment, and the reasonable stocking amount can be calculated according to the formula within the range of the optimum fish carrying capacity: stocking amount (tail / cubic meter) = total weight per cubic meter at harvest / average weight per fish at harvest.

3. Stocking conditions and operation require that fish species must stop eating 2 days before stocking and transportation. The water temperature at the place of departure and destination should be roughly the same, and the difference should not exceed 3 ℃ at most. Rainbow trout stocking is best carried out when the water temperature is 8 ℃ ~ 10 ℃. The higher the water temperature is, the more serious the stress is, which is easy to cause death. Fish transportation should be carried out in spring, preferably with oxygenated live fish carriers, and pay attention to the change of water temperature and the supply of oxygen in the process of transportation. Stocking time should be in the lowest temperature in the morning or when it is rainy and cloudy. The whole process of entering the fish into the box should be carried out in the water, and the operation should be careful to reduce the stress to the fish as much as possible and prevent the fish from scraping, stunning and even death. If the fish is in good health and carefully operated, the survival rate of the fish can reach 100%.

IV. Feed feeding and storage

In the process of cage culture of rainbow trout, it is very important to feed high-quality pellet feed, which must be fully nutritious and contain more than 40% protein. The fish species that have just entered the water have not yet formed the feeding habit, so they should be domesticated in time until the feeding amount is adjusted reasonably after the group takes the initiative to feed.

In the process of culture, the appropriate particle size should be selected according to the fish body size, and the feeding amount should be adjusted in time according to the change of fish body weight, and the feeding time should be in the early morning or dusk. Observe the feeding and digestion of rainbow trout every day to strictly avoid overfeeding. Feed carefully and slowly to the center of the cage to avoid feed flowing out of the cage as far as possible.

The feeding behavior of fish is the best sign of the health status of fish, and the active feeding of fish means that they are in good health. therefore, in order to maintain a strong appetite of fish, 80% of each feeding should be based on the weather, water temperature and digestion.

The quality of the produced feed decreases with the extension of storage time, and the fresh feed needed for rainbow trout must be used up within one month, and too much feed can not be purchased for storage at one time. Not feeding feed with deteriorated or damaged nutrients due to improper transportation and storage can effectively prevent rainbow trout from nutritional diseases. therefore, attention should be paid to moistureproof, sunscreen and rodent damage in feed storage to ensure ventilation and dryness in the storage area.

V. Daily management

The uneven growth of rainbow trout is a common phenomenon. Screening should be carried out once a month, and the breeding efficiency can be improved by grading the fish. When the water temperature rises in summer, the cage depth should be deepened and the culture density should be reduced so as to increase the activity space of rainbow trout. Keep inspecting the cage every day, measure the water temperature, record the feed feeding and fish intake, and find out the sick and dead fish in time; in windy weather, you can take the cage for inspection immediately after the wind stops to see if the cage is damaged and repair it as soon as it is found. and re-tighten the steel wires and clasp screws between the cages to ensure that each connection is firm. Always pay attention to the change of the water level in the culture area, and with the rise or fall of the water level, the iron anchors and wire ropes at the four corners of the fixed operating platform should be collected and released in time. Attachments are easy to be produced around the box, hindering the exchange of water bodies. When more attachments are found, the net should be lifted immediately to clean the cage. The operation should be light and slow, and do not use too much force, otherwise it will scratch the body surface of the fish and cause disease.

VI. Disease prevention and treatment

Rainbow trout is generally not easy to develop, the common diseases are rotten fin disease and nutritional diseases, and generally occur in early spring. In the early spring season, with the gradual rise of water temperature, we should appropriately reduce the breeding density, screen the fish boxes in time, and operate carefully, so as to reduce the mutual infringement of fish bodies and man-made injuries. At the same time, adding appropriate amount of medicine to the feed every week can improve the immunity of fish and effectively prevent the occurrence of rotten fin disease. If fish with broken fins are found, they should be immediately taken out and bathed in potassium permanganate solution and raised separately to prevent infection. Nutritional diseases are mainly caused by substandard feed. As long as the feed is fresh and nutritious, the occurrence of the disease can be prevented. As long as prevention in advance and proper measures are achieved, all kinds of diseases in cage culture of rainbow trout are less common.