What are the points to note when stocking freshwater crayfish?
In recent years, crayfish have become a darling of the dining table, with their value multiplying. It is predicted that the crayfish market will not become saturated within the next 5 years, and crayfish farming is rapidly expanding in various places. After several years of production practice, the author believes that the following points should be noted when stocking crayfish:
Pond selection The pond for farming crayfish should be moderate in area, generally 20 mu to 50 mu. The slope ratio of the pond embankment should be large, at 1:2.5 to 1:3, to facilitate burrowing and reproduction by crayfish, while also reducing crayfish escape. The pond should be rich in natural food organisms and aquatic plants.
Thorough pond clearing 10 days before stocking crayfish, drain the pond water and use 100 kg of quicklime per mu to thoroughly clear the pond. Kill harmful organisms and various pathogens. Apply 100 kg to 200 kg of organic fertilizer per mu to cultivate food organisms.
Ecological planting Plant aquatic plants in the shallow water around the pond perimeter, with the aquatic plant area accounting for 40% to 60% of the pond area. Species include Vallisneria, Elodea, Hydrilla, water hyacinth, water lettuce, etc., which can both provide food for crayfish and serve as ideal places for crayfish to hide and rest. In addition, aquatic plants can also be tied into grass bundles on the pond bottom, placed every 5 m, with each bundle weighing 5 kg to 10 kg, sunk to the bottom, and 15 to 20 bundles placed per mu. The grass bundles are tied with rope, with the other end of the rope fixed at the water surface.
Selection of broodstock Because artificial breeding of crayfish is not yet fully mastered at present, crayfish seedlings are mainly obtained through natural reproduction, so the selection of broodstock is particularly important. The time for selecting and stocking crayfish parent shrimp is generally from the end of August to mid-October, and they can be caught from farming ponds or natural waters. Male and female parent shrimp are required to come from different waters to reduce inbreeding. Parent shrimp should not be out of water for more than 2 hours, though in indoor or humid environments the time can be appropriately longer. Identification of male and female: (1) The first and second abdominal legs of male shrimp evolve into white, calcareous tubular copulatory organs; the first abdominal legs of female shrimp degenerate, and the second abdominal legs are feathery. (2) The genital pores of male shrimp open at the base of the fifth pair of walking legs and are not obvious; the genital pores of female shrimp open at the base of the third pair of walking legs, where a pair of obvious dark round holes can be seen. (3) For adult shrimp of similar body length, the claws of male shrimp are thick and large, and the spines on the carpus and palm are long and obvious; the claws of female shrimp are relatively smaller.
Stocking of parent shrimp The parent shrimp to be stocked are required to be robust, with intact appendages and uniform size, and should be stocked in sufficient quantity at one time, avoiding stocking in batches, which can reduce mutual cannibalism. When stocking parent shrimp, they should be evenly distributed around the pond perimeter with uniform placement points. For parent shrimp transported over long distances, during stocking first soak the parent shrimp in water for 3 minutes to 5 minutes, then place them at the pond edge for 2 minutes to 3 minutes, repeating 2 to 3 times, so that after the parent shrimp absorb enough water, slowly put the parent shrimp into the pond, which can improve the survival rate of stocking. The male-to-female ratio of parent shrimp is usually 2 to 3:1. Crayfish can mate and lay eggs in autumn and winter, and the mating season is generally from September to December. In early March of the following year, when the air temperature rises to 12 degrees C and the water temperature rises above 10 degrees C, some shrimp will leave their burrows to come out for feeding and activity. At this time, management should be strengthened, and artificial feed should begin to be provided. When the water temperature reaches above 18 degrees C, feeding should be intensified. When a large number of juvenile shrimp have hatched, ground cages can be used to catch parent shrimp that have already reproduced.
Stocking density For ponds mainly farming crayfish, stock 30 kg to 40 kg of broodstock per mu, with a size of more than 30 g each. After stocking parent shrimp, feed artificial feed in a timely manner. From April of the following year, begin catching with ground cages and shrimp cages, catching the large and leaving the small, with an annual yield of 200 kg to 300 kg per mu. After that, only harvesting is needed each year, with no need to stock broodstock. It should be noted that catching should not be excessive. If catching is excessive, the yield in the coming year will inevitably be greatly reduced, and at that time supplementary stocking will be needed. For mixed-culture ponds, stock 10 kg to 20 kg of broodstock per mu, with a size of about 25 g each, without feeding feed, mainly relying on natural food in the pond and residual feed in the fish pond. From April of the following year, begin catching with ground cages, catching the large and leaving the small, with a yield generally of 50 kg to 100 kg per mu.