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The quality of river crab species
The scientific name of river crab, Eriocheir sinensis, is rich in nutrients and delicious. It is one of China's traditional luxury aquatic products. The adaptability of crabs, miscellaneous feeding habits, wide source of bait, and easy-to-reach growth environment requirements have resulted in a large area of ​​artificial breeding of crabs. The crab seedlings are an important basis for breeding crabs. High-quality seedlings are one of the key factors for the success of crab breeding. China's currently cultivated crabs are mainly produced from the Yangtze River, Gull and Liaohe rivers. It is extremely important to master the quality identification technology of crab bells. First, the normal species of crab and precocious crab morphology differences (1) the concept of precocious crab and the danger of precocious crab species individuals and large-size crab species, but the body has matured mature small green crab Including a winter precocious crab and a small individual after two winters "green crab". Its side sexual characteristics (mature traits) are exactly the same as mature commercial crabs. Under normal circumstances, the gonads of crabs reach maturation in the late autumn and early winter of the second year, and they die after breeding in the third year of spring. Their life span is generally 24 months. If you mistakenly introduce the precocious crab species as normal crab species, it will cause great losses. Precocious crab species generally begin to die in the southern end of March and early April, and in the north they begin to die from the end of April to the beginning of May. The mortality rate is about 60% to 90%. Most of the dead individuals are 15 grams to 20 grams each. The loss is extremely heavy and the damage is extremely great. (2) External morphological characteristics of male mature individuals The density and color of chelate villi are the main basis for distinguishing the maturity of crab species. Crabs of normal crab species do not have villi or sparse and short villi, and their villi color is mostly pale yellow. The villus of sexually mature crab species is dense and long, and the distribution of villi is close to the base of the immobile finger, the base of the movable finger and the inner and outer sides of the palm joint. The foot bristles show short and fine appearance on normal crabs, while the precocious crabs have thick and long bristles. The body surface color of normal crab species is light yellow or yellow, while sexual mature crab species are mostly dark green. Some obvious spots can be seen on the steps of normal crabs, but not on precocious crabs. The crab male individuals have two pairs of crossovers, born on the first abdominal segment to the second abdominal segment. The color of the normal crab species is dark white, while that of the precocious crab species is white porcelain. The hardness of the transfer device is also the main basis for distinguishing between mature stages. The normal crab type relay has a low hardness and is not osteogenic. It is like a plastic tube when squeezed by hand. It is easy to bend when bending, and the precocious crab species has a greater hardness and has been boned and bent. When it is easy to break, it is not easy to bend. The same is true for the two pairs of crossbars. (3) Morphological characteristics of female mature individuals The color of mature and immature individuals of female crabs is the same as that of male crabs, ie mature individuals are dark green and immature individuals are pale yellow. Abdominal umbilicus shape and abdominal margin villi are the main basis for distinguishing whether the female crab is mature or not. The ventral umbilicus (abdomen) of the crab is flat and is in close contact with the ventral surface of the chest. Individuals with smaller crabs, whether male or female, have a narrow, long, slightly umbilicus umbilicus. With growth, the male umbilicus still maintains a triangular umbilicus, also known as a pointed umbilicus. However, as females grow and develop, the abdomen becomes gradually larger and rounder, also known as the umbilical cord. The umbilicus can completely cover the breastplate. On the edge of the abdomen, when the individual matures, thick and dark villi appear. At the same time, thick velvet hairs are also produced in the abdominal section 1 to section 4. The immature individual's abdomen is approximately triangular. The thoracic plastron did not completely cover the abdomen and umbilicus. A part of the rim of the plastron was exposed. The edge of the thoracic thoracic vertebrae and the sparsely distributed soft hairs of the abdominal limbs. The anatomical results can also be seen in the obvious differences between normal and precocious crab species. When the carapace was lifted off, mature crabs showed purple brown or bean-colored ovaries on both sides of the stomach and below, and the entire ovary showed an "H" distribution in the crab body. The normal crab species had no obvious purple-brown ovaries that were easily visible to the naked eye. Larger normal crab species had a transparent, milky-white ovary and a small volume, weighing less than 1% of body weight. Second, the differences in the morphology of different river crab crab species China's currently cultivated crabs mainly come from the Yangtze River, Lancang River and Liaohe three major water systems, due to the different geographical conditions of the three major water systems, resulting in Yangtze River Crab, Lijiang River Crab and Liaohe Crab in Large differences in morphology. The turtles of the Yangtze River water system are blue-green, oval in shape, and have four sharp side teeth on the margin of the shell. The fourth side teeth are prominent, the middle depression of the frontal teeth is obvious, and the second and third steps are equal in length and without bristles; Liaohe Aquatic crabs are irregularly oval in shape with black backs, grayish yellow belly, short stepping feet, opaqueness, and less prominent salivation-like protrusions below; The festival is short, cyan, with sparse hair and a square body. The crab body has a distinct smell. In addition to the morphological differences, there are certain differences in the growth, development and reproduction of the three major river crabs. The Yangtze River Crab has fast growth, large commodity specifications, and good quality. The Liaohe Crab has a good ability to adapt to adverse environments, but the commodity individuals are small, and the reproductive migratory began in August. It is more than a month earlier than the Yangtze River Crab and there are no fishing peaks. Mature individuals 50 grams to 125 grams, fast growth in the early stage of production, slow growth in the later period; Long Jiang crab growth is slow, commercial individuals are smaller, sexual maturity is early, generally more mature in the year.
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