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Early health breeding techniques of crab
In view of the fact that the survival rate of bigeye larvae in the river crab is low, after years of practice and research, the quality and survival rate of river crab seedlings have been greatly improved. The early health breeding techniques of crabs are described below. 1 Temporary rearing and warming of broodstock crabs Due to market reasons, river crabs are stocked early in the spring (also related to the low temperature tolerance of river crabs). Therefore, in recent years, the breeding time of river crabs has been advanced. It is generally admitted to the room before mid-March, but the temperature of the pro-crab is slower than usual. One is the poor physical fitness of the pro; the other is that the outdoor temperature is low before entering the room, and the gonads of the pro-crab are almost undeveloped. If the temperature is raised quickly, the young larvae are weak, the yield of the nursery is low, the quality of the seedlings is poor, and even the breeding fails. Therefore, the pro-crab temperature should be grasped as: from the day of the crabs to the hatching 30 ~ 35d is appropriate. Temperature increase method, when water temperature is lower than 10°C, 1°C is added every 2d; after water temperature is 10°C, 1°C is added every 3d. 2 Salinity and temperature of crab breeding The salinity of crab breeding is about 26 ,. When all the metamorphosis is zoea v, the salinity drops to 22 ‰ to help increase the metamorphosis rate of big larvae. After the larvae became larvae, the salinity was gradually adjusted to less than 5 出 before emergence. The incubating temperature for crab breeding was: 18-20°C, 22°C for juvenile larvae, 23°C for iliac zoea, 24°C for iii to iv juveniles, and 25°C for juvenile juveniles. Bigeye larvae are 26°C. 3 Density of cloth pool density for crab breeding The density of cloth pool for crab breeding should be reasonably arranged according to the designed output and the comprehensive conditions of the nursery. It is generally recommended that the density should not exceed 300,000/cubic meters. 4 Water quality management of river crab breeding 4.1 According to the situation of larval density and feeding amount, the amount of water exchange in each period should be reasonably grasped. It is recommended to change the amount of water as follows: The water is the main stage of the juvenile larvae, and the water is changed by 1/5 every day in the zoea stage. The zoea cubs changed water by about 1/2 per day in the iii phase, while the variegated larvae changed water by about 2/3 per day in the iv phase, and the varia larvae in the v phase and the big eye larvae changed water by 100% per day. 4.2 In the late stage of zoea, ie iv and v phases, 110e-6 potassium permanganate is applied before changing the water to purify the water and improve the quality of water exchange. 4.3 The nursery ponds regularly apply photosynthetic bacteria or other biological agents to make beneficial bacteria form dominant populations, degrade ammonia nitrogen, purify water quality, and inhibit the growth of harmful bacteria. 5 The principles of feeding the crabs and feeding the crabs during the breeding of crabs are based on the principles of freshness, palatability, and quantity but not excessive amounts. Crabs in the early period of healthy seedlings, less suitable fresh live bait, mainly to substitute bait. Feeding of substitute bait should pay attention to the appropriate conversion and quantity of different types of bait. The types of bait substitutes in different periods are described below. The juvenile period, period II, the appropriate amount of egg yolk, algae powder, shrimp slices, yeast, mini bait and a small amount of rotifers (fresh or frozen). The juveniles of the zoea were fed in the appropriate amount of Artemia nauplii after the stage of anaphase change. The zoea larvae, iv, iv, and v were fed mainly with appropriate amount of cakes and mini baits, plus rotifers, and a certain amount of Artemia nauplii was fed according to the number of larvae. After the large-eyed larvae have become homozygous, the processed shrimp or Artemia adults (live or frozen) are fed. 6 Prevention and cure of disease during crab breeding The common diseases of crab breeding are polycondensation (or single worms) and filamentous bacteria. It is recommended to take precautions and pay attention to the following three points: 6.1 Strictly sterilize the nursery ponds and disinfect the crabs before hatching. 6.2 A reasonable understanding of the amount of feed and water exchange combined to maintain good water quality. 6.3 During the nursery period, photosynthetic bacteria or other biological agents are regularly applied to the nursery ponds to form beneficial bacteria and inhibit the growth of harmful bacteria.