When is it appropriate to breed crayfish seedlings? When is the best time to plant? (Three stocking times a year)

Crayfish are also known as procrayfish, red crayfish and freshwater crayfish. When raising crayfish, naturally go back to put shrimp seedlings, so when is it more appropriate to raise crayfish seedlings? When is the best time to release seedlings?

Lobster seedling breeding

1. Parent shrimp selection

Parent shrimp can be selected in September-October of last year or March-April of the same year, with a body weight of 30-50g, complete appendages, health and disease-free, strong activity, and a female-to-male ratio of 2-3:1. Male and female lobsters have obvious characteristics in appearance and are easy to distinguish.

When ① reaches sexual maturity, the male individual is significantly larger than the female.

② male dragon foot is thick, there is a bright red molluscum on the outside of both ends of the dragon foot, the female dragon foot is relatively small, most of the female feet do not have red molluscum, even if there is a light color.

The ③ male reproductive foramen opening is at the base of the fifth pair of foot, and the female reproductive foramen opening is at the base of the third pair of foot.

The abdomen of ④ sexually mature female shrimp is dilated, while that of male shrimp is relatively narrow.

2. Parent shrimp cultivation

The area of parent shrimp pond should be about 1200m2, the bottom material should be loam, the water depth is about 1m, the width of the pond is more than 1.5m, there is sufficient and good water source, the injection and drainage outlet is built, and the surrounding ridge is built with plastic film or calcium plastic board to prevent escape wall. 7-10 days before stocking, the pond is disinfected with 50-60kg/ per mu raw lime dry pond. After disinfection, the depth of water injection was about 1m after filtration (preventing wild mixed fish into the pond), and 500-800kg/ mu of rotten livestock and poultry manure was applied to improve the water quality. Put people in the pond for shrimp climbing shelter, such as branches, roots, bamboo tubes, etc., and transplant some aquatic plants.

Parent shrimp ponds can put 40-60kg/ mu of parent shrimp and soak in 3% salt water for 10 minutes before stocking to kill pathogens. In order to make full use of the water body and regulate the water quality, 50-100 silver carp and bighead carp can be mixed cultured at the same time. During the cultivation period, fresh water plants, bean cakes, wheat bran or formula feed can be fed, and some animal feed can be added. Such as chopped snail clam meat, livestock and poultry slaughtering scraps and so on. Daily feed: 2% of the body weight of parent shrimp in March, 4%-5% in April, 6%-8% after May, once in the morning and once in the evening, accounting for 70% of the daily diet. At the same time, the management of water quality should be strengthened, changing fresh water once every 10-15 days, and sprinkling 10-25g/m2 with quicklime every 20 days to maintain good water quality and promote gonadal development of parent shrimp.

3. Parent shrimp reproduction

From April to May, when the water temperature is above 20, parent shrimp begin to mate. The fertilized eggs are hatched into young shrimps in the belly of female shrimp, and the incubation time is 40-70 days. After hatching, the juvenile shrimp completed the growth and development process under the protection of the mother. As soon as the juvenile shrimp leaves the mother, it can take the initiative to feed and live independently. When it is found that there are a large number of young shrimp in the breeding pond, the seedlings should be collected in time for shrimp seedling cultivation.

4. Parent shrimp overwintering

The lowest survival water temperature of lobster is 5 ℃. However, when the water temperature is lower than 9 ℃, the mortality rate of shrimp about 3 cm is very high during the overwintering period. Although adult shrimp can survive, there will be a large number of deaths after 2-3 months. Therefore, to do well the overwintering work of parent shrimp and ensure the water temperature of 16 ℃-18 ℃ during the overwintering period is also an important part of the whole breeding work.

The method of overwintering of parent shrimp is the same as that of Macrobrachium rosenbergii, and the commonly used overwintering methods are plastic film covered pool heat preservation method, electric heater heating method, hot spring water overwintering method, factory residual hot water overwintering method and glass chamber overwintering method, which can achieve the safe overwintering effect of parent shrimp.

5. Seedling raising technology

Although the number of eggs held by lobsters is small, the fertilization rate can be more than 98%, and the hatching rate can reach 80% to 85%. The problem is that the young shrimp grow and molt frequently after emergence, which is easily restricted by environmental conditions and affect the breeding rate. In order to improve the rate of raising seedlings, the key points are as follows:

① water quality requirements

During the lobster breeding period, the water body should be relatively stable, the water quality should be fresh, the pH value should be between 6.5 and 8, the temperature difference between day and night should be prevented, and the dissolved oxygen in the water should be kept above 5.6 mg / L.

② water environment

There must be water floating lotus on the surface of the water (accounting for 1), and there should be water plants at the bottom and hidden caves to increase the molting attachment of shrimp seedlings, and it is also convenient to grasp the emergence time and the growth of shrimp through seedling washing inspection. Fences and filters are added to the water inlet to prevent enemy creatures from entering the pond, to prevent frogs from entering the pond to lay eggs, and to prevent tadpoles from eating shrimp seedlings. At the same time, it is necessary to prevent parent shrimp from clinging to and escaping.

③ strengthens inspection

Insist on checking the emergence of larvae in the morning and evening, and when the larvae are free from the mother, catch the parent shrimp in time and return to the parent pond for re-cultivation, so as to minimize the stocktaking through the pond, and be very careful in the operation to avoid affecting the parent shrimp holding eggs and the newly hatched shrimp.

④ guaranteed feeding

Rotifers and other small zooplankton were cultured in time to feed the newly hatched shrimp. It is estimated that 3-5 days before emergence, a small number of small zooplankton were caught from the special feed pond into the shrimp seedling pond. And use cooked egg yolk and soybean milk to replenish the food supply for young and young shrimp in time.

Juvenile shrimp culture

I. Cultivation requirements.

When the young shrimp leaves the mother, it is usually carried out in the juvenile shrimp pond. after all the young shrimp leave the mother, the parent shrimp will be removed, leaving the young shrimp to breed. At this time, the average body length of the young shrimp is 0.8 cm. After 15 days of cultivation, the body length can reach 2.4-3 cm. For farmers to carry out adult shrimp culture and production.

(1) cultivation pool requirements

The cement pond with an area of 20-40m2 and a water depth of 0.6-0.8m is the best for juvenile shrimp ponds, and the soil ponds are also acceptable, but the newly built cement ponds should be dealkalized first, which should be close to the water source, good water quality, convenient injection and drainage, build escape prevention facilities and disinfect the ponds (the method is the same as that of parent shrimp cultivation). After disinfection, fermented organic fertilizer 500kg/ mu was applied to cultivate plankton to feed the juvenile shrimp. At the same time, tree roots and bamboo tubes are set up to provide habitat, molting and concealment for young shrimp.

(2) Water requirements

① water quality generally uses river water or well water, the water quality should be fresh. At the inlet, filter the water with a sieve to prevent insects, aquatic animals (such as water centipedes), small fish and shrimp and eggs from entering the pond. During the cultivation period, depending on the residual feeding of sewage and the condition of water quality (such as ammonia nitrogen and other three-state nitrogen on the high side), it is necessary to absorb sewage and change water regularly in order to maintain good water quality.

The suitable range of ② water temperature is 27 ℃-29 ℃, and the change range can not exceed 2 ℃. If the water temperature is lower than 20 ℃, the growth rate will be reduced, which will seriously affect the survival rate, so it is necessary to keep the water temperature relatively stable during the whole cultivation period.

③ dissolved oxygen content Young Shrimp leaves the mother, and the breeding pond should be inflated continuously throughout the day to make the dissolved oxygen in the water sufficient.

④ PH value the pH value of the water used for cultivation should be controlled at 7-8.5. if the water quality is found to be acidic, quicklime can be used to adjust the PH value. In breeding farms that use tap water for small-scale production, baking soda can be used to adjust the PH value.

2. Cultivation technology

The stocking amount of juvenile shrimp is generally 150-230 / m2, which should be consistent with the specification of shrimp fry in the pond, and release in sunny morning or cloudy day. Soymilk can be fed 3-4 times a day in the first week after stocking; from the second week, animal feeds such as small fish and shrimp, clam meat, earthworms and silkworm pupae are mainly fed, properly mixed with corn, wheat and paste feed, once in the morning and once in the evening, 40% of the daily feed in the morning, 0.25-0.40kg per 10,000 young shrimp in the early stage, and about 10% of the shrimp weight later. During the culture period, the water was changed once every 10 days, and the raw lime water was sprinkled every 20 days with a concentration of about 20g/m3 to regulate the water quality. After 25-30 days of cultivation, the body length of young shrimp can reach 3cm, and then it can be transferred to adult shrimp culture.

Stocking time of crayfish seedlings three times a year

The time of the first release of crayfish seedlings:

From late March to early April, the overwintering seedlings of the improved variety Tangkou were used and 4000 crayfish seedlings were released per mu. The aquatic plants or bamboo leafy vegetables in the pond are arranged before releasing seedlings, accounting for about 50% of the total area of the pond. At the beginning of spring, fresh minced fish and shrimp were fed alternately with pellet feed, 1.5 kg dry feed per mu (3 kg fresh minced fish pellets) per mu per day, and gradually increased feed amount by 0.5 kg per mu every 5 days, and 5 kg per mu every day until 1 month after stocking. 45 days after stocking, the crayfish can be caught again when the number of crayfish reaches 34 million / kg.

The time of the second release of crayfish seedlings:

From late May to early June, after clearing the pond and removing the wild, the late spring seedlings were relatively large, generally 120,160 / kg, about 22.5kg and 4000 crayfish seedlings per mu. After seedling release, boiled wheat grains (boiled with 1% salt until the wheat grains blossom) were fed with 5 kilograms per day and stopped on rainy days. At the same time, bamboo leafy vegetables were planted in early June, accounting for about 50% of the total area of the water body. The second crop of crayfish culture should pay attention to prevent flight and frequent replacement of new water, and in early September, before the listing of river crabs on the market. In the middle and later period of the second crop of shrimp culture (50 days after the release of seedlings), the crayfish were caught in cage every day, and the crayfish were screened and put on the market.

The time of release of crayfish seedlings for the third time:

From mid-late September to early October, autumn-propagated early seedlings were released, and the amount of seedlings per mu was appropriately increased, about 5000 seedlings per mu of water, and 200 million small and medium-sized shrimp seedlings per kilogram were selected. Feed the processed minced fresh fish and shrimp feed to promote the fattening of parent shrimp in winter. The amount of feed depends on the weather and water temperature, the weather is good, the water temperature is above 20 ℃, and the daily feed rate is 2.5 million kg per mu (the amount of fresh material is doubled). When the water temperature is lower than 20 ℃, the feeding amount is reduced by 50%, when the water temperature is below 15 ℃, the feeding amount is further reduced by 50%, and when the water temperature is lower than 10 ℃, the feed feeding can be stopped. When the daily water temperature is lower than 10 ℃, the amount of water injected into the pond should be increased to reach the highest water level of the pond and retain water to survive the winter. When the water temperature of the pond gradually returned in the second year (early March), it was caught in time.