At present, in the production of crab culture, there is a prevalence of 20% to 30% of precocious puberty crabs, sexually mature crabs no longer grow, the specifications are generally 50 to 80 grams each, the commodity value is extremely low; once the sudden change of weather, Reproductive migration can be carried out in advance, and the catch rate is low; if it continues to be raised, the mortality rate is extremely high, and it can generally reach about 80%. Seriously affected the efficiency of crab breeding.
1. Characteristics of sexually mature crabs
(1) Female crabs of sexually mature crabs have lumps in the abdomen. The male crab-transplanter becomes a rigid, osseous tubular body. The cheiropodal hairs are dense and dark in color, and the cross-linker becomes a rigid, osteogenic tubular body. .
(2) Sexual mature crabs are uneven on the back with dark green or blue.
(3) Sexually mature crabs can be seen in the liver area with two purple strips and eggs, or two white masses, the testis.
2. Reasons for the formation of sexually mature crabs
(1) The fed baits are too refined, especially if the animal feeds are fed too much in the early stage, which leads to excessive intake of animal foods that cause bulimia and excess nutrients in the body, leading to premature sexual maturity of the crabs.
(2) The effective accumulated temperature increases. Due to the small aquaculture water and shallow water level, the water temperature in the growing season has always been high, and the water volume temperature is too high, thereby accelerating the gonadal development of the crab.
(3) Inadequate stocking density led to premature growth and premature sexual maturation.
(4) The high salinity of water body stimulates the gonadal development of crab.
(5) Germplasm resources are degraded. With the expansion of the scale of crab farming, the introduction of species between the regions increased, the migration of southern crabs, the migration of northern crabs, and the artificial breeding of long-term non-renewing parents, resulting in mixed, degenerate crab species, slow growth, sexual maturity ahead of schedule.
3, preventive measures
(1) Select the authentic Chinese mitten crab species in the Yangtze River water system to maintain scientific and reasonable stocking densities.
(2) Scientific feeding. Due to water conditions, control the amount of feed, in particular to control the amount of animal feed. The pre-breeding baits are mainly plant-based baits, supplemented by animal baits.
(3) Properly increase the water depth of the pond. The growth season is generally required to reach 1.8 meters or more. During the hot season, it is better to change the water. It is better to use the water in the river channel and the lake to reduce the water temperature.
(4) Transplanting plants in aquaculture ponds with a coverage rate of about 50%, with less direct sunlight, reduce the effective accumulated temperature of crab growth.
(5) During the growing season, crab ponds splash lime, photosynthetic bacteria, and bromochlorogenic drugs every 20 days to disinfect water bodies, reduce the concentration of organic matter in the water, and promote healthy growth of crabs.
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