With the mitigation of contradiction between the supply and demand of river crabs in southern China, the northern crabs provided by Yunnan, Tianjin, and Liaoning are generally boycotted in the south. The production of crab breeding in the southern provinces is steadily developing, and the economic benefits are stable, resulting in the crab seed market. The center of gravity moved south and a large number of northern technicians went south. Due to the difference in natural conditions, there are great differences in the breeding methods of crabs between the South and the North. Correct understanding of these differences and mutual learning can ensure the smooth progress of nursery production and reduce errors. For this reason, based on my experience in the three years of Tangshan in Hebei and Nantong in Jiangsu, the author made a comparison of different ways of breeding crabs in the south and the north for reference.
1. Development of crab source, production promotion, and holding of crabs Southern crabs and crabs are generally taken from local rivers, lakes, and large ponds. Although the disordered flow of river crab species has caused mixed strains in recent years, their main quality characteristics are still Approaching pure river water crabs, the time for promoting production is generally selected before and during the early spring. Since the market price of southern crabs is high at both ends and low in the middle, it is required that the crabs be as early as possible before the time of production promotion, and early spring should be as late as possible. Early emergence can be early emergence, but the time should not be earlier than mid-November, too early due to immature gonadal development, affecting the fertility rate and embryo quality, early spring to promote production as late as possible, can delay the nursery time, but time should not be later than 3 At the beginning of the month, in March, as the water temperature rises, the gonads begin to degenerate, affecting the quality of fertilization and embryos, and ultimately affecting the metamorphosis rate from Z1 to Z2.
In order to ensure the rearing crabs for the rearing crabs, in addition to adopting the method of delaying mating, more methods of refrigerating crabs from previous years were used to control the development of embryos, and the refrigerated locations can be selected from constant temperature storage and underground pools. However, no matter where it is stored, the time taken from the earthen pond should be performed before the natural water temperature rises to 8°C. In the early stage of storage, the water temperature should also be controlled below 8°C. Otherwise, the embryonic development will start and the embryo will gradually develop to the heartbeat. Period, long-term heartbeat without breaking the membrane, will consume the endogenous nutrition of the larvae, making the Z1 to Z2 metamorphosis difficult. During the whole cold period, feed the high-quality food properly. Hang it with silk string and replace it in time.
There are two sources of crabs in the north. First, the local crabs are generally mature in the middle and late October. They can mating and hold eggs. After the eggs are hung, there is still half a month's feeding and nutrient accumulation. Northern crabs have a long wintering period, and spring crabs are relatively thin. At this time, the mating rate is low, embryo quality is poor, and Z1 is difficult to metamorphose to Z2.
Another source of northern crabs is the Yangtze River crab, mostly due to cooperation with the South to provide seedlings from the South. The sexual maturity of the Yangtze River Crab is about one month later than that of the Liao River Crab. Therefore, in the appropriate mating season in the north, the development of gonads in the Yangtze Crab is still immature. When the gonads of the Crab are mature, the water temperature in the North is already too low to hold eggs. Therefore, it is better to use the crabs of the Yangtze River in the north, and it is better to use the eggs directly from the south when the temperature is lower in the spring.
2. North and South differences in nursery conditions Northern crabs use natural seawater for their nursery. Whether they are wintering or growing, the salinity changes little and is relatively high, generally between 20 and 30. The PH value of seawater is above 7.8, and the PH value of well water for desalination seedlings is not less than 7. During the production period, there is more abundant monophyletic algae in the water, and rotifers and Artemia can partially or fully meet production needs.
There are natural seawater and artificial seawater in the southern river crab breeding. The salinity of natural seawater changes greatly. Especially in the rainy season, not only the salinity is unstable, but the acidity and alkalinity are acidic. It is very troublesome to raise the seedling production, and it is only controlled by quicklime. PH value. In addition, the fresh live animal feed that can be eaten by larvae in the south is extremely small, and it is only fed by substitute bait and frozen animal bait, and the water quality is easily deteriorated. Due to the significant differences in nursery conditions, the differences in production operations are determined.
3. Different ways of raising seedlings from north to south
(1) Cloth density and larval density control: The amount of seedlings depends on the water quality conditions, the quality of the feed, and the management level. In the south, the density of seedlings is generally between 15 and 200,000/m3, and there are cloths up to 400,000-600,000/M3. After Z2, it is divided into pools. The reasons for the low density of seedlings are: After Z1 is changed to Z2, the juvenile bait is mainly live larvae, and the diet is good. The live brine worms can also reduce the fat of the bottom water to make the water fresh, thus ensuring the survival from Z1 to Z5. The rate is relatively high. On the contrary, if there are too many seedlings, it will inevitably increase the demand for Artemia larvae, increase the cost of seedling cultivation and the difficulty of management, especially the post-larval dying due to excessive density, and bring great losses to seedling production. Therefore, for the sake of safety in production, the seedling density should not be too large.
The density of northern seedlings is generally controlled at 50-600,000/m3, and in individual cases, it reaches 1.5 million/m3, and can also be successfully changed to Z2. The density of seedlings in northern crabs is not very strict, and the density of each period is mainly determined depending on the status of each stage of metamorphosis and water quality, and the quality of fresh live bait. Based on the experience of breeding in 1994 and 1995, and according to the data of some local high-yield farmers, the author summarized the optimal density and limit density of the larvae of river crabs in Tangshan, Hebei Province.
(2) Inflation method and water quality management: In the north, the inflating method mostly adopts aerated gas to inflate. The density of aerolite is one per m2. In the late stage of nursery, the accumulation of residual baits, feces and floating mud forms a layer of foul smell. The layer of foul smell is covered by the oxide film of the surface layer. It will not affect the nursery for a certain period of time. If the smelly bottom is turned up due to the movement of the loose stone or other factors, it will often cause the death of the seedlings. Therefore, the northern nursery shall be replaced with normal water change. To often pour the pool, the pool time is generally selected in the Z4 period and the next day of bigeye larvae.
Southern inflatable methods are scattered gas stone and plastic tube drilling two ways, plastic tube drilling more use 1.5-2cm hard plastic tube, keep the tube spacing 30cm, eye distance 20cm, this method is evenly filled, not easy to form a foul bottom, Inflatable eye is not easy to block, it is the ideal way of inflation. The Southern Nursery, which uses aerated gas to inflate, often uses the suction method to suck out dirt from the bottom of the tank, which is troublesome and difficult to clean.
(3) Feeding of bait: Northern river crab breeding, Z1 relies on fertilizer to increase water cell monolins, and is accompanied by egg yolk, soymilk and yeast, and Z1 feeds rotifers on the second day and feeds it to Z5. Artemia larvae Z2 began feeding and increased the feeding amount as the larvae grew. Z5 began to feed small Artemia adults. When the above-mentioned foods were insufficient, they were filled with egg yolks, cakes, shrimp, etc., and they entered the big eyes and were mainly fed. Live Artemia adults. The southern stage of Z1 is similar to that of the North, and Z2 is mainly Artemia larvae until Z5. It enters the big eyes and feeds on frozen Artemia, Copepods, Cladocera, and fish gills.
(4) Desalination of crab seedlings: The date of desalination and desalination of crab seedlings are basically the same in the north and south, but the desalinated water in the south is sometimes acidic and must be taken care of, otherwise it will lead to a large number of deaths in the desalinating period. If desalinated water has a PH value of less than 7, sprinkling lime into the distribution tank should be started by spraying 50kg per 1000m2. The pH of the water should be measured while spreading, until it reaches 7.5 or more, and the conditional nursery can be Planting a certain amount of plants in freshwater sedimentation tanks can also improve the overall water quality of desalinated water.
1. Development of crab source, production promotion, and holding of crabs Southern crabs and crabs are generally taken from local rivers, lakes, and large ponds. Although the disordered flow of river crab species has caused mixed strains in recent years, their main quality characteristics are still Approaching pure river water crabs, the time for promoting production is generally selected before and during the early spring. Since the market price of southern crabs is high at both ends and low in the middle, it is required that the crabs be as early as possible before the time of production promotion, and early spring should be as late as possible. Early emergence can be early emergence, but the time should not be earlier than mid-November, too early due to immature gonadal development, affecting the fertility rate and embryo quality, early spring to promote production as late as possible, can delay the nursery time, but time should not be later than 3 At the beginning of the month, in March, as the water temperature rises, the gonads begin to degenerate, affecting the quality of fertilization and embryos, and ultimately affecting the metamorphosis rate from Z1 to Z2.
In order to ensure the rearing crabs for the rearing crabs, in addition to adopting the method of delaying mating, more methods of refrigerating crabs from previous years were used to control the development of embryos, and the refrigerated locations can be selected from constant temperature storage and underground pools. However, no matter where it is stored, the time taken from the earthen pond should be performed before the natural water temperature rises to 8°C. In the early stage of storage, the water temperature should also be controlled below 8°C. Otherwise, the embryonic development will start and the embryo will gradually develop to the heartbeat. Period, long-term heartbeat without breaking the membrane, will consume the endogenous nutrition of the larvae, making the Z1 to Z2 metamorphosis difficult. During the whole cold period, feed the high-quality food properly. Hang it with silk string and replace it in time.
There are two sources of crabs in the north. First, the local crabs are generally mature in the middle and late October. They can mating and hold eggs. After the eggs are hung, there is still half a month's feeding and nutrient accumulation. Northern crabs have a long wintering period, and spring crabs are relatively thin. At this time, the mating rate is low, embryo quality is poor, and Z1 is difficult to metamorphose to Z2.
Another source of northern crabs is the Yangtze River crab, mostly due to cooperation with the South to provide seedlings from the South. The sexual maturity of the Yangtze River Crab is about one month later than that of the Liao River Crab. Therefore, in the appropriate mating season in the north, the development of gonads in the Yangtze Crab is still immature. When the gonads of the Crab are mature, the water temperature in the North is already too low to hold eggs. Therefore, it is better to use the crabs of the Yangtze River in the north, and it is better to use the eggs directly from the south when the temperature is lower in the spring.
2. North and South differences in nursery conditions Northern crabs use natural seawater for their nursery. Whether they are wintering or growing, the salinity changes little and is relatively high, generally between 20 and 30. The PH value of seawater is above 7.8, and the PH value of well water for desalination seedlings is not less than 7. During the production period, there is more abundant monophyletic algae in the water, and rotifers and Artemia can partially or fully meet production needs.
There are natural seawater and artificial seawater in the southern river crab breeding. The salinity of natural seawater changes greatly. Especially in the rainy season, not only the salinity is unstable, but the acidity and alkalinity are acidic. It is very troublesome to raise the seedling production, and it is only controlled by quicklime. PH value. In addition, the fresh live animal feed that can be eaten by larvae in the south is extremely small, and it is only fed by substitute bait and frozen animal bait, and the water quality is easily deteriorated. Due to the significant differences in nursery conditions, the differences in production operations are determined.
3. Different ways of raising seedlings from north to south
(1) Cloth density and larval density control: The amount of seedlings depends on the water quality conditions, the quality of the feed, and the management level. In the south, the density of seedlings is generally between 15 and 200,000/m3, and there are cloths up to 400,000-600,000/M3. After Z2, it is divided into pools. The reasons for the low density of seedlings are: After Z1 is changed to Z2, the juvenile bait is mainly live larvae, and the diet is good. The live brine worms can also reduce the fat of the bottom water to make the water fresh, thus ensuring the survival from Z1 to Z5. The rate is relatively high. On the contrary, if there are too many seedlings, it will inevitably increase the demand for Artemia larvae, increase the cost of seedling cultivation and the difficulty of management, especially the post-larval dying due to excessive density, and bring great losses to seedling production. Therefore, for the sake of safety in production, the seedling density should not be too large.
The density of northern seedlings is generally controlled at 50-600,000/m3, and in individual cases, it reaches 1.5 million/m3, and can also be successfully changed to Z2. The density of seedlings in northern crabs is not very strict, and the density of each period is mainly determined depending on the status of each stage of metamorphosis and water quality, and the quality of fresh live bait. Based on the experience of breeding in 1994 and 1995, and according to the data of some local high-yield farmers, the author summarized the optimal density and limit density of the larvae of river crabs in Tangshan, Hebei Province.
(2) Inflation method and water quality management: In the north, the inflating method mostly adopts aerated gas to inflate. The density of aerolite is one per m2. In the late stage of nursery, the accumulation of residual baits, feces and floating mud forms a layer of foul smell. The layer of foul smell is covered by the oxide film of the surface layer. It will not affect the nursery for a certain period of time. If the smelly bottom is turned up due to the movement of the loose stone or other factors, it will often cause the death of the seedlings. Therefore, the northern nursery shall be replaced with normal water change. To often pour the pool, the pool time is generally selected in the Z4 period and the next day of bigeye larvae.
Southern inflatable methods are scattered gas stone and plastic tube drilling two ways, plastic tube drilling more use 1.5-2cm hard plastic tube, keep the tube spacing 30cm, eye distance 20cm, this method is evenly filled, not easy to form a foul bottom, Inflatable eye is not easy to block, it is the ideal way of inflation. The Southern Nursery, which uses aerated gas to inflate, often uses the suction method to suck out dirt from the bottom of the tank, which is troublesome and difficult to clean.
(3) Feeding of bait: Northern river crab breeding, Z1 relies on fertilizer to increase water cell monolins, and is accompanied by egg yolk, soymilk and yeast, and Z1 feeds rotifers on the second day and feeds it to Z5. Artemia larvae Z2 began feeding and increased the feeding amount as the larvae grew. Z5 began to feed small Artemia adults. When the above-mentioned foods were insufficient, they were filled with egg yolks, cakes, shrimp, etc., and they entered the big eyes and were mainly fed. Live Artemia adults. The southern stage of Z1 is similar to that of the North, and Z2 is mainly Artemia larvae until Z5. It enters the big eyes and feeds on frozen Artemia, Copepods, Cladocera, and fish gills.
(4) Desalination of crab seedlings: The date of desalination and desalination of crab seedlings are basically the same in the north and south, but the desalinated water in the south is sometimes acidic and must be taken care of, otherwise it will lead to a large number of deaths in the desalinating period. If desalinated water has a PH value of less than 7, sprinkling lime into the distribution tank should be started by spraying 50kg per 1000m2. The pH of the water should be measured while spreading, until it reaches 7.5 or more, and the conditional nursery can be Planting a certain amount of plants in freshwater sedimentation tanks can also improve the overall water quality of desalinated water.
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