Shrimp and crab pond polyculture of American hard-shell clam technology
_ Yu Mengmeng, etc
American hard-shell clams are also known as small round clams, northern curtain clams, and American curtain clams. Hard-shelled clams are wide-temperature, wide-salt shellfish that grow fast and have delicious flesh. The hard-shell clam is found on the Atlantic coast of the United States and is one of the main economic shellfish in the shallow seas and tidal flats of the region, with high nutritional and economic value. Rizhao Institute of Oceanography and Fisheries undertakes the national shrimp and crab system Rizhao shrimp and crab test station has 16 acres of shrimp and crab breeding ponds, has been engaged in shrimp and pike crab breeding experiments, in 2018 the introduction of American hard shell clams and Chinese shrimp, pike crab pond polyculture, over the years the breeding effect is better, the yield is higher, has a higher promotion value.
First, the biological characteristics of hard-shell clams
Hard-shell clams belong to the bivalve and curtain clam family, with larger individuals, the largest individual is more than 200 grams; the shape is triangular oval, the shell is thick, the outer surface is smoother, and there are very obvious and fine growth wheel patterns; the shell surface has yellow or yellowish brown patches, and the shell edge is brown or black-cyan. Hard-shell clams grow mostly in soft substrates containing shells, and are distributed in sandy depressions, sandy mud depressions and mud bottoms. The optimal growth temperature of the hard shell clam is about 20 °C, and the growth stops when it is above 31 °C or below 6 °C; it can still survive at low temperature and 0 °C. The tolerance salinity of the hard-shell clam ranges from 15 to 48, and the tolerance to salinity increases with growth, but it is inversely proportional to temperature, and the survival rate is significantly reduced when the salinity is low and the temperature is high. The growth of hard-shell clams is greatly influenced by seawater movement and algal nutrition. The ideal conditions for growth are a gentle current coupled with proper algae density accompanied by 4 mg/L dissolved oxygen. In the Rizhao region of Shandong Province, the water temperature is 20 to 26 °C in June and July every year, and the hard shell clams begin to lay eggs.
Second, the pond polyculture of American hard-shell clams
In March 2018, Rizhao Institute of Oceanography and Fisheries purchased 240 kg of hard-shell clam seed from Zhejiang, 1 500-1 600 grains/kg, and mixed with shrimp and crabs in the breeding pond of the Rizhao Shrimp and Crab Experimental Station of the National Shrimp and Crab System in the Institute.
1. Culture ponds and conditions
Rizhao Marine and Fisheries Research Institute has 4 open-air shrimp and crab breeding ponds, rectangular, with an area of about 16 acres. Each pond has its own inlet and drainage pipes with independent gates. The bottom of the pond is a mixture of sediment and sediment, with a depth of about 2.5 m, a water depth of 1.6 m, and a 0.3 m deep ring ditch at the bottom of the pond.
2. Preparation before seedling release
(1) Pool bottom cleaning. After about two months of dry dew and exposure in winter, the bottom of the pond is removed by a small excavator in mid-to-late January, the mud at the bottom of the pond is cleaned up, and the middle area of the pond is leveled to facilitate the drilling of hard-shell clams. A ring trench of 0.3 m deep and 2 m wide was excavated around the bottom of the pond.
(2) Disinfect the pool. At the beginning of February, the pond is 30 cm of water, bleach powder 50 ~ 80 g / m3 clear the pond disinfection, after 3 days, add natural seawater, inlet pipe nozzle set 80 mesh sieve silk mesh filter to prevent entering the predatory aquatic organisms, add water to 60 cm.
(3) Cultivate animal and plant bait. The pond is 60 cm deep, and in mid-February, live hook shrimp were purchased from Tao Luo, put into the pond at a density of 5 kg/mu, and animal bait was cultivated; micro-ecological agents and organic fertilizers were used to sprinkle the whole pond to promote the reproduction of phytoplankton in the pond water as the basic bait in the early stage of breeding. After that, continue to add water, add 5 to 10 cm of natural seawater every day, and according to the color of the water in the breeding pond, use micro-ecological preparations and organic fertilizers in a timely manner, so that the color of the pool water remains yellow-brown or yellow-green, and the transparency of the pool water is maintained at 25 to 40 cm. By the time of stocking of hard-shell clams, the water depth of the culture pond needs to reach more than 80 cm.
3. Seed selection and stocking
(1) Seed selection. Hard-shell clam seedlings should be selected from well-sized high-quality fresh clam seedlings, with a size of about 1 500 grains/kg, and the shell crushing rate is less than 5%.
(2) Seed stocking. Hard-shelled clams are stocked in late March, Chinese shrimp are stocked in early April, and pike crabs are stocked in early May. The stocking density of hard-shell clams was 22 000 to 24 000 grains/mu, the stocking density of Chinese shrimp was 8 000 fish/mu, and the stocking density of pike crabs was 8 000/mu.
4. Management of breeding period
(1) Water depth and water quality control. In the early stage, add 5 to 8 cm of natural seawater every day, and add water to 1.2 meters after 1 month. Whenever the pond is flooded, about 10% of the water is changed, and 15% of the water is changed in the middle and late stages and high temperature periods. Continue to add water so that the pond water depth reaches and maintains 1.6 m. Keep the water fresh, so that the color of the pool water is yellowish brown or yellow-green, and the transparency of the pool water is maintained at 25 to 40 cm. If the water transparency of the pond is less than 25 cm, it needs to be regulated by water exchange or water addition; if the transparency is greater than 40 cm, it needs to be regulated by using micro-ecological preparations and organic fertilizers.
(2) Feed and feeding. Early ponds had cultured hook shrimp live bait that did not need to be fed. Fish feed began in early May, and the fish feed mainly includes fresh trash fish and shrimp caught in the sea (frozen trash fish and shrimp are used instead of frozen trash fish and shrimp during the fishing moratorium), mussels, shrimp maggots, etc. In the early stage of breeding, it is mainly fed fresh miscellaneous fish and shrimp caught in the sea, mainly feeding mussels and small trash fish as a supplement in the middle stage, and feeding miscellaneous fish and shrimp and maggots in the later stage of breeding, so that shrimp and crabs can be fattened and fattened. Every day at about 4 p.m., the amount of seawater trash fish and shrimp is fed intensively, and each pond is fed 5 kg in the early stage; with the growth of shrimp, crabs and shellfish, the amount of feeding is gradually increased, and the feeding amount of each pond is increased to about 30 kg in the later stage, and the feeding amount is appropriate to have no surplus within 2 hours, which can be appropriately increased or decreased according to the feeding situation.
(3) Oxygenation. The pond is equipped with 2 1.5 kW nano-aerators, 1 for use and 1 for backup. Oxygen increase time: 9 pm - 6 am starting in early June, 6 pm - 6 am in July and August, and returning to 9 pm to 6 am after September.
(4) Disease prevention and daily management. Disinfect with povidone iodine every 15 days or so. Breeding ponds are specially managed, patrolling the ponds every morning, middle and evening, observing the water quality, feeding of farmed animals, salvaging dead shrimp and crabs, timely adjusting the amount of feeding and water replacement, and adding biological agents and organic fertilizers in a timely manner; inspecting the pond embankment, pipelines, gates, etc., and repairing the damage in time.
3. Summary
In recent years, the shrimp and crab pond polyculture of the American hard shell clam model in the Rizhao Tao Luo and liangcheng area has been recognized and widely used by farmers, farmers according to their own pond conditions, there are shrimp and crab-based polyculture, there are also American hard shell clam-based polyculture, shrimp and crab species are mainly Chinese shrimp, Japanese shrimp and barracuda crab.
From 2018 to 2021, the shrimp, crab and shellfish breeding of the institute was very smooth, and the task of the shrimp and crab test station was completed well every year. In 2020, 16 acres of breeding ponds, pike crabs out of the pond in batches of 2 200 kg, of which 125 g / male pike crab 600 kg in August to supply the local tourism market, 200 g / male pike crab out of the pond 400 kg in the Mid-Autumn Festival, harvested 1 200 kg of yellow female crab in early November, Chinese shrimp out of the pond 1 500 kg, 30 size / kg; American hard shell clam harvested a total of 12 000 kg, 30 size / kg.
The pond polyculture experiment is mainly based on shrimp and crab culture, with reasonable combination of American hard shell clams. The purpose of polyculture of hard-shell clams is to effectively use the water body space of the culture pond, regulate the water quality, maintain the ecological balance of the pond, and improve the economic benefits of the culture. This polyculture model can not only increase the yield of shrimp and crabs, but also produce good environmental conditions for the cultivation of hard shell clams, which significantly improves economic benefits and is conducive to increasing fishermen's income.