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The biological characteristics of ayu and its breeding techniques
Ayu is a relatively promising aquaculture species. Although Ayu is a migratory fish, it can also grow in habitat in fresh water for a lifetime. It can be used for large-surface waters to grow and multiply, and it can also be intensively cultured using cages or flow culture. The artificial breeding of sweetfish started late in mainland China. At present, the artificial breeding of Zhejiang, Hebei and other places is relatively successful, especially the artificial breeding of sweetfish in Ningde District of Fujian Province has developed rapidly, and the artificial breeding of sweetfish in Taiwan has also become more popular. Obviously, the development prospect of artificial breeding of sweetfish is tempting, but to obtain good economic benefits, we must also pay attention to two points: First, we must grasp the timing of sales and sales (especially foreign trade exports). In the international market, especially in Japan, the best time for the sale of ayu is from May to August, and the price is also high. Since then, the price has gradually declined. Until September, few people are interested. The second is to master the sales specifications. The sweet-fish is generally raised to 70 grams to start selling. In Japan, the sales specifications of the market require 65 to 160 grams, that is, 6 to 16 tails per kilogram. Sales at this time, good quality, excellent quality, welcomed by consumers. If the individuals are raised too much, not only the growth rate is slow, the feed coefficient is high, the cost is increased, but also the quality is decreased, the price is decreased, and the loss is not worth the candle. Therefore, we must prevent the missed sales opportunity by blindly pursuing large specifications. (a) Biological characteristics of sweetfish. Ayu, also known as sea-fish, fish, sweet-skinned fish, melon fish, flat fish, August fragrant, fat fish, etc., is also known as Japanese cockroach in Japan. It is a kind of oyster-shaped head, sweet fish species, is an annual small and rare species. As for economic fish, there is also the saying of "fish of the year." It has the reputation of "king of freshwater fish" in the international market. It is mainly distributed in the southern part of Japan's Hokkaido to Kagoshima, the North Korean coast and some of Bohai Sea, Yellow Sea, East China Sea and Taiwan's rivers. The squid body is slender and laterally high, with a small head and a pointed tip, a wide tooth, and a truncated shape. Individual adults are generally about 20 cm long and weigh 80 to 100 grams. Due to geographical differences, there are also differences among natural individuals in different regions. Large individuals up to 30 cm, 400 to 500 grams. The sweet fish has small, sleek scales. There is an oval orange marking behind the lid. The eyes are medium and large. There is no fat eyelid on the side. There are 2 nostrils on each side. Near the eye edges, the front hole is smaller and the back hole is larger. The mouth is large and long and narrow. The posterior edge of the maxilla extends to below the eye. There is a protrusion on the left and right sides of the mandible. The dorsal fins have no hard spines, the caudal fins are forked, and the pectoral fins are short. The body color of sweetfish varies with the environment and is usually black or yellow-brown. The sides of the abdomen are silver-white, the fins are light yellow at the end, and the yellow pimples above the pectoral fins. The anal fins of males in the reproductive season are orange-yellow and "chasing stars" appear on the back and fins. Because of its cheek on the back, it is named after its fragrance. Ayu is a filter-feeding fish. It prefers habitats in rocks or gravel sediments and clear water into Haixi River. It is a type of cold-water fish that prefers high temperatures (10°C to 27°C). There are land-based and floating-type types. Types. In the natural environment, juveniles mainly eat zooplankton, adult fish mainly eat cyanobacteria and diatoms, and also eat insects in water. Ayu is a fish that breeds eggs for the autumn. Juveniles grow up in the lake and in the upper reaches of the river in spring. In autumn, they return to spawning near the estuary. After hatching of the fertilized eggs, the larvae enter the sea and overwinter, and the river grows again the next year. Sweetfish can also live in fresh water for life, and swim along the rivers and lakes. Its eggs are sticky, and their egg production ranges from 10,000 to 100,000 grains, and the maximum number is about 130,000 grains. However, the egg production is generally between 20,000 grains and 30,000 grains. Spawning water temperature 19 ~ 14 °C. Shortly after spawning, all broodstock died. The general trend of ayu fish spawning is early night in the south. The spawning period in Japan is from mid-October to mid-November. The spawning period in Liaoning is from late August to late September, and from early October to early December in Zhejiang. (b) Nutritional value. Ayu contains a variety of essential amino acids, has a good nourishing effect, high food value, delicate meat and fat, aroma, taste delicious. Can be braised, stewed, fried, smoked dried fish and so on. Dried fish is also a great gift for friends and family, such as the dried roast fish in Zhejiang, and the salted grilled sweet fish in Japan are popular delicacies. (C) feed nutrition indicators. In the artificial breeding conditions, ayu is a major animal feed. In foreign countries, especially in Japan, there is a special feed for sweet fish. Specific requirements are: complete nutrition, high water absorption, low hardness, slow settling, good viscosity, not easily lost. At present, there is still a lack of special feed for sweet fish, which can be mixed according to the supply conditions of various regions. Protein content is required to be over 40%. Animal protein is the main ingredient. Generally, animal feed such as silkworm meal, shrimp meal and fish meal can be used as the main ingredient. demand. (d) Main aquaculture technology. 1. Build a field. It is very important to build a field to raise good fish. Farms should be built in areas where drainage and irrigation are convenient and close to water sources, requiring clear water, no pollution, running water or micro-flowing water. Groundwater can also be used. 2. Aquaculture pond area. The aquaculture pond area is generally 100 to 300 square meters (can also be used for rearing ponds) and is made of bricks, etc., requiring good quality, no leakage, circular inside, and the bottom of the pond requires a slight tilt to the middle to facilitate the concentration of dirt. Evacuate near the discharge area. Water depth 60 to 90 cm. If earthen pond farming is used, the pond area is generally 2,000 to 3,335 square meters, and the water depth is 60 to 90 centimeters. There is the best flow of water or micro-flowing water. Before disinfection, clear ponds must be disinfected, killing enemy and harmful creatures, wild fish, etc. To ensure successful breeding. 3. Stocking density. Ayu is a small, economical fish that can be sold for as long as 70 grams. Therefore, the general stocking density is about 80,000 tails per 0.067 hectare, which can be appropriately adjusted according to local climatic conditions, water quality, and feeding and management standards. In order to prevent the occurrence of diseases, medical baths are disinfected before seedlings are sprayed, and antibiotics are used for drugs. The dosage is from 1/50,000 to 1/100,000 of the amount of water. 4. Temperature. The aquaculture water temperature is 15 ~ 25 °C, the optimum water temperature is 18 ~ 23 °C. In a suitable temperature range, the growth rate is proportional to the water temperature, and it is necessary to make full use of favorable light and temperature conditions in summer and autumn to speed up the development. Above 28°C or below 10°C has adverse effects on the growth of sweetfish. At the same time, the seedling stage should prevent drastic changes in water temperature so as to avoid adverse consequences. The minimum temperature for wintering is 2 to 3°C. 5. Feeding. This is one of the most important aspects of aquaculture management. It should be adjusted and adjusted appropriately according to the water quality, water temperature, and the aquarium's living status. In the appropriate growing season, the feed must be invested enough to ensure that the sweet fish eat, eat well, make it healthy growth, increase the yield. The juveniles that have just entered the pool are usually fed 4 to 5 times a day; afterwards, they are gradually reduced, and they are finally fed once and twice a day. Feeding amount is generally 10% to 20% of the fish's body weight, with slight changes in different growth stages. When feeding, observe the fish's feeding conditions and make adjustments. In short, the timing of feeding should be adequate. Feeding too much is a waste of feed, polluting the water quality, but also may induce certain diseases, affect growth, and even cause unnecessary deaths; but also to prevent inadequate feeding, so that the ayu will not eat enough, increase the tail seedlings, affect the growth and out The rate of success may even result in the consequences of killing each other and must be highly valued. 6. Sorting. After a long period of aquaculture, there will be individual differences. Therefore, there are conditions to conduct timely sorting, stocking by different pool sizes to ensure consistent growth. 7. Water quality management. This is another very important link in feeding and management. The water quality must be better and the transparency is suitable to meet the requirements for the growth of ayu fish. Specific attention should be paid to the following water quality indicators. (1) pH. The pH should be controlled at 6.8 to 7.8. Excessively high or low pH values ​​have an adverse effect on the growth of ayu. (2) Ammonia nitrogen. Ayu has higher requirements for ammonia nitrogen. Under normal circumstances, the ammonia nitrogen is low, the growth rate is fast, and the water quality is also good. The pH value is between 7.5 and 7.8. When the ammonia nitrogen is above 210-6, the growth rate is affected. At a pH of 8, the semi-lethal concentration of ammonia to sweetfish at approximately 48 hours is approximately 1.1810-6. Therefore, the aphid is protected from ammonia poisoning. (3) Nitrogen nitrite. The semi-lethal concentration of nitrite nitrogen to Ayu is approximately 2.810-6 for 48 hours, and its safe cultivation concentration should be below 0.310-6. Therefore, under the conditions that ensure the normal growth of ayu, the amount of nitrous oxide should be minimized. concentration. (4) Dissolved oxygen. Higher dissolved oxygen indicates relatively good water quality. The dissolved oxygen suitable for the growth of sweet fish should be above 40%. Below this index, it will often reduce the intake of ayu fish and reduce the feed utilization rate. If it is less than 20%, it may cause death. In short, there are many factors that affect water quality. In addition to the intrinsic factors of water quality, excreta and feed loss of sweetfish will affect water quality. Therefore, pay close attention to changes in water quality and prevent unnecessary losses. (5) Diseases, insect pests and control techniques of sweetfish. Ayu is a relatively easy-to-breed species, and pests and diseases rarely occur, but if it is not properly managed, it can also cause disease. The main diseases are isolated germ disease, third generation worm disease, bacterial rickets, cold water disease and pseudomonas disease. Cold water disease and Pseudomonassis are now described as follows: 1. Cold water disease. Its main symptoms are paralysis, anemia in various organs, bleeding in the lower lid, and empty holes in the body. The temperature of the disease is about 25°C, and bacteria can be isolated to isolate the bacteria. The prevention method is to thoroughly sterilize culture ponds and culture equipment to prevent germs from entering; pay attention to the stocking density, prevent excessive feeding, and avoid random administration. 2. Pseudomonas disease. The disease is caused by gram-negative Pseudomonas monocytogenes infection, which is usually about 30 days after entering the pool. The onset of symptoms is ascites fluid with mixed blood, mild anemia, some visceral punctate bleeding and anus Bleeding. Overfeeding can easily induce the disease. Mainly by improving the defensive performance of organisms by avoiding overfeeding and overdosing, and paying attention to improving water quality.