The squid (plecoglossus altivels) are annual migratory fish. From February to May each year, juveniles (2 cm to 3 cm in length) that have been wintered in the sea are traced back from the estuary and grow and develop in the river, from September to November. Most lay eggs in the middle and lower reaches of the shoal. The brooders lost their bodies after being spawned and died mostly. In order to explore the use of cold-water rivers to carry out cage culture of ayu, from March 25 to July 28, 2003, we carried out experiments on the Dongjiang River in Chenzhou City, Hunan Province, and achieved success. Now the test report is as follows: 1. River conditions Net cages are used to set the Dongjiang River section at the lower reaches of Dongjiang Lake, which is the bottom water flowing from Dongjiang Lake. The perennial water temperature is 13°C to 15°C. The water volume, water level, and flow velocity are less affected by the climate and the water depth is 2.5m to 3.0m. The flow rate is 10cm/s, the transparency of the water body is more than 3.0m, and the water source is the drinking water source for urban residents. The width of the river is about 500m, and the bottom of the river is sand and gravel. The net cages are made of nylon mesh cloth, and the specifications are 5.0m4.0m1.5m, open type, a total of 160, and the total area of ​​the cage is 3200 square meters. The cages were set on the water surface of the river 3.0m from the river bank on February 16. They were arranged in tandem with the direction of the water flow. 40 cages were used in 1 row. Every 2 rows were set up. Each cage was set between rows. There is a 1.0m wide walkway to facilitate the production and management of ayu. The distance between the cage group and the group is 3.0m. The cage draught depth is 110cm to 120cm, and the height of the exposed water surface is 30cm to 40cm. Angle steel is used as a cage frame, and an iron drum is used as cage floater. In addition, in order to make the draught part of the cage develop square in water, ropes or bricks should be hung on the four corners outside the bottom of the cage. Second, the source of the fingerlings and the stocked fingerlings are from Ningde, Fujian, and oxygen bags are used to store oxygen and transport ice. The first batch of 300,000 summer fishes and the second batch of 500,000 fish were transported to their destinations on February 28 and March 18, respectively, and placed in cages in the Dongjiang River section, respectively. Each cage was stocked. 20,000 ayu. Before putting the fish into the cage, place the oxygen bag containing the fish directly on the surface of the cage for 15 minutes to 20 minutes, and slowly turn the oxygen bag so that the water temperature in the bag is basically the same as the water temperature in the cage. Then, unzip the bag to allow the river to slowly enter the bag until it is full. Then, use one hand to press the oxygen bag into contact with the water. The other hand slightly lifts the other end of the oxygen bag so that the aroma fish in the bag slowly flows into the cage. in. Third, feeding and management 1. Feed the fish into the box after the first 2 days after the feed is not fed to allow the fish to adapt to the environment; fish into the box after the first 3 days began feeding a special feed for sweet fish. The fingerlings of the fish species were bred during the breeding period, and they were fed 6 to 8 times per day. Adult fish were fed the adult fish with aquaculture feed and fed 2 to 3 times a day. Feeding methods are: slow feeding, fast feeding when the fish species form feed, and slow feeding when the fish species snatch food is weakened, and finally they stop feeding when some fish are found to have left the feeding. . Moderately fast and slow grasp: fish easier to feed to the feed without causing the feed to sink. At the same time, feed feeding sites should choose one end of the water tank facing the water surface to prevent feeds from being drained out of the cage as water flows out of the cage. The first 20 days after the ayu fish species are placed in cages is the critical period for the adaptation period, domestication period, and the survival rate of sweet fish. In particular, the aroma fish will produce feed for feeding due to the unfavorable environment in the initial period of culture. Not interested in, or even refused to eat, the phenomenon of a large number of dead fish in this period. The key technology to solve the problem: First, adjust the flow rate of the water in the cage to 3cm/s~5cm/s to reduce the physical energy consumption of the ayu. The second is the characteristics of the albino fish that do not like the strong light. Above the water surface of the cage, set a shade net with the same area as the cage. The shade net is a black single layer and is 2.0m to 2.5m away from the surface of the water to create a cool environment where ayu fish species are more suitable. Third, increase the number of feedings. The sweet fish “eat less mealsâ€, feeding 6 times to 8 times a day, each feeding 40 minutes to 60 minutes, the specific time should be based on the actual accompaniment of the situation of flexible food intake. When feeds are fed, care should be taken not to over-concentrate fish populations, or the food intake among fish populations will be extremely uneven. The density of the school of fish can be adjusted by feed feeding, that is, to enlarge or reduce the area that the feed is fed on the surface of the water to make the density of the fish smaller or larger, so as to ensure that the fish in the school are fed uniformly. 2. Disease prevention and control Anti-disease aquaculture, as long as the water quality is good and the fish is not injured, while scientific feeding, it is generally not easy to disease. In the prevention and treatment of fish diseases, four main measures are taken: First, the cage dirt is promptly removed to maintain the normal exchange of water inside and outside the cage, to ensure that there is sufficient dissolved oxygen in the water body; second is to feed high quality, palatable fish feed. And only feed to the fish body full of 80%; Third, careful operation, when cleaning the net box to pull the net movements should be light, the speed should be slow, fish inspection or test to do with water, do not bring the fish with The water surface; Fourth, in all operations, including fish species transportation, fish bodies should be avoided as far as possible. In case of injury, fish should be applied in time to prevent diseases. 3. Day-to-day management First, visit the cage every morning, evening and evening to observe carefully the feeding and activities of the aquarium and the changes in water speed and water temperature, and establish a file for fish culture. Second, prevent the waste from drifting into the cage. In order to avoid eating fish by mistake, at the same time, it is necessary to remove the attachments on the cages in time to ensure clean and unobstructed meshes. The third is to clean the cages regularly and check the cages for damage and timely repair. The fourth is to keep the cage openings. 30cm to 40cm above the surface of the water to prevent a sweetfish from escaping to escape; the fifth is to divide the boxes in time to keep the specifications of the sweet fish in each cage basically the same, which is conducive to fish feeding and growth. From the summer flower till the tail is weighed at 20g, although it is large, it is divided into boxes every 10 days to 15 days. After every 20 days, it is divided into boxes one at a time, taking into account the growth of individual individuals. When the bins were sub-binned, the density of sweet fish in the cages was gradually dilute. That is to say, the original stock of 20,000 fish per cage was gradually dilute until the last cage of each mouth was stocked with about 5,000 fishes. IV. Test Results After the first batch of sweetfish was cultured for 138 days, a total of 1991.50kg of sweet fish was harvested, 265500 fishes, and the average individual weight was 75g per tail. The second batch of sweetfish was cultured for 120 days and a total of sweet fish was harvested. 24,561.60 Kg, 438,600 tails, individual average body weight 56 ​​g/tail. The breeding survival rate is 88.1%, the average yield is 14.64kg/m2, and the feed coefficient is 1.2. V. Discussion 1. The experiment showed that sweetfish are suitable for large-scale cage culture in the Dongjiang River section, and there are nearly 1,000 hectares of water from the reach to the lower reach of the Qiaokou reach and Feitianshan reach. Box more than 30 million square meters. 2. Experiments show that the growth rate of sweetfish in the Dongjiang reach is slower than that of the origin. The author believes that: First, because the water temperature of the Dongjiang reach is low, the problem can be solved if it is properly moved downstream; Second, the transparency of the water body is good. There is no shortage of water in the water, and human interference is too great, which affects the normal growth of sweet fish. 3. The aquarium seedlings do not like the light, especially before the individual's body weight is 20g, shading nets should be used to cover the ayu fish cages to avoid direct sunlight. When the individual body weight of sweetfish reaches 20g or so, the sunshade net should be removed in time to enhance light, so as to promote the growth of ayu fish and delay its gonadal development, thereby ensuring the good quality of sweet fish. 4. Naturally, sweetfish like to eat algae attached to the pool wall. In cage culture, the quality of sweet fish can be increased if algae is added.
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