Australian freshwater lobster is native to Oceania and is a large-scale freshwater prawn introduced from Australia in recent years. It includes two species of red crayfish and crayfish. The shrimp lives in fresh water for life. It is omnivorous and has a fast growth rate. It can reproduce naturally in fresh water. It has a high survival rate and strong resistance to disease. It is weak in attack, resistant to hypoxia, and resistant to pollution. It has strong adaptability, delicate meat, delicious taste, high edible ratio (abdominal weight accounts for 42% to 47% of the total weight), and it has the advantages of long-distance transport, live availability, simple artificial propagation equipment, and low cost. According to the research conducted by the Beijing Fisheries Research Institute on the introduction of two Australian freshwater lobsters, the growth rate of the red-handed crayfish is faster than that of the crayfish, and the low temperature tolerance of the crayfish is stronger than that of the red crayfish. This chapter focuses on the biological characteristics and culture methods of red-caught crayfish. ??
(i) Ecological habits?
1. Morphological characteristics?
The entire body of the crayfish is covered by a chitin shell and is short and thick. The body color is blue-green. It is composed of cephalothorax and abdomen. The length ratio is approximately 1:1. The first pair of feet is thick and cheroidal, and its ends are enlarged. Clamp-shaped, it is the main tool to defend against enemy intrusion, self-defense and hole-breaking. In other steps, the second and third steps are chelate-like, and the fourth and fifth steps are claw-like. ?
Red chelonian crayfish has strong adaptability, low oxygen tolerance and high temperature resistance. The habit of red-claw crayfish is nocturnal, it lurks in places where water can hide during the day, it feeds in the evening and before dawn, it is like night activities, it is not good for swimming, and it crawls in the bottom of the pool. During the mating season, all red snapjacks are active during the day. The culture experiment showed that the survival temperature of the red crayfish ranged from 5 to 35Â°C, and the suitable growth temperature was from 13 to 28Â°C. When the water temperature exceeded 13Â°C, it began to ingest. When the water temperature exceeded 30Â°C, growth was inhibited. The shrimp will make holes in unfavorable living conditions. It has been observed that in the softer pool sediments, there is very little burrowing during the breeding process, but during the overwintering process, the shrimp must be punched. ?
Red-claw crayfish have strong resistance to low dissolved oxygen, such as the water can still survive when dissolved oxygen in the water is 1 mg/l, but they can survive for a long time under moist and micro-water conditions, often found in the process of breeding or overwintering. Red crayfish appear on the dike. The larvae and broodstock should not be in a low-oxygen environment, as this will result in the death of larvae and egg embryos. Therefore, the dissolved oxygen should not be less than 4 mg/l in the breeding process, and the amount of dissolved oxygen should be higher during the incubation process.
The red clams are omnivorous animals, and they mainly eat organic detritus, algae, filamentous algae, roots, leaves and fragments of aquatic plants under natural conditions. Especially, they prefer green and juicy plants such as water lilies. , water hyacinth, Malay-eyed dish, narcissus, and bitter grass. Animal foods include oysters, clams, eggs of aquatic insects, cockroaches, snails, cockroaches, and fish. In the case of artificial breeding, compound feeds, by-products of the processing of agricultural and sideline products (cakes, rice bran, bran, etc.), leftovers from slaughterhouses, and a variety of delicate terrestrial grasses, fruits and vegetables, etc., can be fed. The feed in this shrimp farming is relatively easy to solve. ?
4. Reproduction and growth?
There is no definite breeding season for Crayfish. When the water temperature is between 20 and 30Â°C, it can be propagated all year round, and there are multiple spawning phenomena. The amount of egg laid varies with the size of the individual. Generally, about 1,000 eggs are produced per year. The fertilized egg adheres to the abdominal part of the female and hatches. The hatched larvae still adhere to the abdominal part of the female. Time, after several times of molting, only left the mother to live free. ?
The crayfish are repeatedly molted during the entire growth from juvenile shrimp to adult shrimp. Under proper environmental conditions, the time interval of each newly hatched juvenile shrimp is shorter, and it takes 1 to 2 days to cover the shell one time. With the growth of the body, the time between shells is also prolonged. During the oyster shell, the shrimp is most prone to attack by predators or the like and is a dangerous period for the shrimp to cause death. If during this period, human capture, moving, poor water quality or lack of oxygen is more likely to die. ?
Red-clampfish have strong climbing ability and like to go to land on night or rainy days. Therefore, the ponds that raise the red-claw crayfish must have anti-escape facilities. The facilities used for the escape prevention of red-crawled crawfish can be made up of earth walls, brick walls and plastic panels with cornices, which are about 40 cm high. ??
(b) artificial breeding?
Red-claw crayfish can spawn several times a year, and the length of daylight has a certain effect on its reproduction. There is no spawning phenomenon when the water temperature drops below 20Â°C. When the water temperature rises from 20Â°C, mating and oviposition occur gradually. The shrimp is well-fed and can reproduce 2 to 3 times a year. ?
1. The choice of broodstock?
(1) The requirement of broodstock requires the selection of prawn for adult shrimps with strong vigor, complete appendages, smooth body, no attachments, and diseases (such as tail rot and shell damage). In order to achieve high fertility, we must choose giant crawfish with a body length of 9 cm or more, good maturity, and high spawning power. In addition, we must group by size, and select the males that match them. ?
(2) Male and female identification of red-claw crayfish males was larger than females, and the male prawn had two bright red and soft membrane plaques on the front side of the two chelipeds. The appearance was easily distinguishable from females. ?
(3) Ratio of male to female Under natural breeding conditions, the proportion of males and females is similar to that of Macrobrachium rosenbergii, but females need slightly more. In the breeding process, a ratio of 2 to 1 is more appropriate. ?
2. Feeding and breeding broodstock?
After entering the wintering pond, the adult shrimps formed in earthen ponds must be bathed in formalin at a concentration of 20010-6? for about 10 minutes to remove the attached organisms before they can be moved into the broodstock pool. ?
(1) The cultivating pool is divided into cement pool and earthen pond. The choice of a nursery pond must consider the following:
1 production scale. According to the scale of production, a suitable broodstock cultivation pond is selected. However, regardless of the size of the site, its location should be good water supply, convenient drainage and irrigation, fresh air, quiet environment, free from natural and man-made interference. ?
2 area. The area should be adapted to local conditions. Large-scale production is generally more than 80 square meters, and it can even be 2,000 square meters or more. The water body is large and the water quality is relatively stable; small-scale production of the cultivation pond can be several to ten square meters. ?
3 water depth. It is generally 50 to 60 cm. During the wintering period, especially the soil in the earthen ponds should be deepened. This is beneficial to the constant water temperature and reduce energy waste. ?
4 water quality. The general requirement is that the water quality should be fresh and the dissolved oxygen should be high. In particular, the dissolved oxygen requirement during the intensive cultivation is above 4 mg/l. The temperature during the winter should be controlled at 16-18 Â°C. ?
5 concealed objects and escape prevention facilities. In order to prevent the broodstock from killing each other, bamboo baskets, hanging nets, bamboos and other concealed objects are placed in high-density breeding ponds. Since the broodstock during the wintering in the earthen pond is easy to make a hole, the best way to prevent it is to add cement on the slope of the pool, and use a plastic film around the dyke to stop the escape wall with a height of 30 cm. ?
(2) Restocking of broodstock Before broodstock is stocked, the cement pool should be cleaned and sterilized. The earthen pond should be used to remove silt, dirt and residual feeding, fix loopholes, and do a good job of anti-escape, drainage and irrigation and thermal insulation facilities. In general, broodstock before entering the pool, the general use of lime or bleaching agents and other drugs to disinfect the pool water, and then broodstock stocking. The density of stocking is directly related to the breeding effect of the broodstock. If the stocking density is too large, the growth and development of the broodstock will be poor. If the stocking density is too small, the pool, manpower and material resources will be wasted. Generally depending on the area of â€‹â€‹the pool, the breeding season, the physiology of the broodstock and the size of the individual determines its stocking density. According to the production practice experience, about 20 shrimps of 16/kg can be placed per cubic meter of water. ?
(3) Breeding and management of broodstock Since broodstock have a small amount of eggs, it is necessary to increase the survival rate of the broodstock in order to ensure the production of seed production. In cultivation and management, we must maintain good water quality, rich nutrition, adequate oxygen and suitable temperature, and good anti-escape facilities. ?
Good water quality makes the broodstock have a very good living environment. Generally, water and drainage should be added depending on the color, transparency and weather conditions. Change the water once every 3 to 4 days, change the water of 1/3 of the pool each time to ensure good water quality. Nutrients are the material basis for the gonad development in broodstock. In addition to putting a small amount of aquatic plants (such as water hyacinth) in the pond, the early culture is generally fed with shrimp and crab pellets with high protein content. In places where conditions permit, especially in the process of warming and strengthening cultivation, increasing the feeding of some animal feed such as small fish, clams and shellfish will promote its growth and development. The feeding amount is generally 4% to 5% of the body weight of the broodstock, and it is increased or decreased depending on the feeding condition. Residues must be sucked off regularly to avoid deterioration of water quality. Oxygen can be oxygenated regularly during the overwintering process and must be continuously oxygenated during the process of strengthening management. When culturing and raising temperature, the temperature is controlled at 28 to 30Â°C. In addition, during the wintering in the earthen pond, it is necessary to do a good job of preventing fleeing, because in very cold days, the red crayfish will make holes. ?
(4) The lowest survival temperature of the broodstock shrimp in winter is 3Â°C. However, through observation during the production process, when the water temperature is lower than 9Â°C, the broodstock with a mortality rate of 3 cm is high during the overwintering period and the adult shrimp is able to survive, but after 2 to 3 months, a large number of deaths will occur. Therefore, do a good job of broodstock overwintering work to ensure that the water temperature during the winter during the 16 ~ 18 Â°C, but also an important part of the entire breeding work. ?
1 The main facilities for wintering. The method of overwintering of broodstock is the same as that of Macrobrachium rosenbergii. Common methods for overwintering include plastic film covering pool insulation method, electric heater heating method, hot spring water overwinter method, factory residual hot water overwinter method and glasshouse overwinter method, etc. The purpose of safe wintering for broodstock. ?
2 strengthen cultivation. Red clam crayfish can generally hold eggs 2 to 3 times a year, the breeding period is 5 to 10 months, the prosperous period is 6 to 8 months. Each shrimp has 40 to 1400 eggs. At this stage, broodstock must be spawned several times for spawning, and each time it is bred, it consumes a large amount of nutrients in the body, and its constitution is significantly weakened. In addition, when hatchlings and broodstock hatch young shrimps, the mother shrimps should be promptly removed from the nursery and fed with enough feed so that sexual maturity can be achieved again. After all the juvenile shrimps are detached from the mother shrimps, the mother shrimps immediately start mating and spawning and begin the next breeding process.
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