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In view of the destruction of the marine ecological environment, the living environment of mud snails is deteriorating, the area of ​​the beach where it grows has gradually decreased, and the natural resources have been severely degraded. With the rising selling price of mud snails, large-scale artificial breeding has been carried out in various coastal areas, and it has become an important species of shellfish shellfish culture in our city.
One, muddy biology
(I) Morphological characteristics
The body of snails is rectangular and slippery. The front end is mostly called the head plate, and the rear end is called the mantle. The head of the mud snail is large and very plump. It is crawling, has no antennae, and has degenerated eyes. It is buried in the skin of the head plate. Lateral development is well-developed, with most of the outer shell covered. Later, it becomes hypertrophic, with free leaves. The shell of mud snail is behind the head plate and occupies about 1/2 of the body. Shells only cover the internal organs. The shells of the mud snails are oval in shape and very large. The shells are crisp and thin, yellow or white, and their shells do not cover the entire body. No spiral tower and umbilical, self rotation, wide shell mouth, smooth screw axis, no flaws. Muddy adult can see many fine lines on the outer surface of the shell, and the inner edge of the shell mouth is smooth.
(B) Ecological habits
The mud snails inhabit the tidal flats along the coast, coating them with muddy or soft muddy beaches, and they can also live normal in sandy bottoms. In the inner bay beaches where there are no storms and rapids, the most dense. In the coastal areas of Zhejiang, it is vertically distributed in the mid-tide zone to the low-tide zone, and the mid-lower zone to the low-tide zone is the most, with the ups and downs with the seasonal changes. Mud snails are painted on the sea and crawl on the beach surface after ebb tide. In rainy days or colder weather seasons, using the head plate to excavate the sediment and submerge in the surface of the sand, it is not easy to find out. After the sun comes out, it climbs out of the mud and feeds on the beach. In the summer, the tide area is high, and in winter, the tide area is low.
The survival temperature of adult snails is -1.5 to 33C. The temperature range is 0-30C, and 10-25C is the optimum temperature. The specific gravity range is 1.005 to 1.020, and the pH range is 3.74 to 9.0. The optimum pH is pH6.11 to 8.01. Bullacta exarata has strong tolerance to dried dew, and it still has a survival rate of 60% after being exposed for four months in spring, and it is relatively weak in summer.
Bullacta exarata is a foraging gastropod. When feeding, the tooth tongue is pulled out to pick up food on the muddy surface. Its diet is omnivorous. The main types of bait are benthic diatoms, in addition to large amounts of organic debris, silt and small crustaceans, invertebrate eggs, etc., but there is no strict selectivity for food.
Bullacta exarata is a life-growing shellfish, also an annual shellfish. The growth of planktonic larvae is slow. The growth of larvae grows faster. After growing into a snail, it grows slowly and slowly. The shell height increases to about 15 mm and the gonad begins to mature. After maturation, most of the individuals died after mating.
(III) Breeding habits
Bullacta exarata is a hermaphrodite, a type of alien fertilization. The female and male sex glands of the mud snails are called together and are called "bisexual glands." They are located on the left side of the screw and sandwiched in the liver cells. They are light green to light yellow when mature. The testis is usually located in the middle, surrounded by ovaries, and the sexes tube in the middle of the testes. However, there are also male and female germ cells coexist in one follicular cavity, or mixed distribution of male and female reproductive follicles. The mature age of snails is one-year-old, that is, the young snails that were bred in the previous year reached the maturity of the gonads in June of the following year. The breeding season of snails is from the end of March to the end of November. From May to June and from September to October, there were two obvious peaks of reproduction. Sexually mature mud snails mate on mudflats. The mating time is approximately 15 minutes. The time from mating to spawning is approximately 4 days. At the time of spawning, the head and two holes of the mud snail exposed the mud surface, and the latter part was buried in the mud. A thin colloidal bag was first produced from the hermaphroditic reproductive hole, and then the egg and colloidal filler were discharged into the bag. Spread evenly on the inner wall of the bag. When the ovulation is completed, the gum shank of the egg bag is produced, and one side of the egg is buried in the sand and the egg group is fixed in the sand. The entire spawning process takes about one hour. Spawning is usually done in the afternoon or the middle of the night and can produce 1-2 egg bags at a time. The egg in the egg group is the fertilized egg, and the embryo is developed in the egg bag. The fertilized egg hatches out of the membrane after four days of development and swims freely in the water. The larvae swim in the seabed after 2-8 days of floating metamorphosis. On the completion of the development process, after a month of feeding became young snails.
Second, the production of snails
The species that are currently cultivated in the nudibranch are mainly derived from harvesting of natural seedlings in the sea area, cultivation of earthen ponds, etc. All artificial seedlings are also being studied.
(I) Natural seedlings in sea areas
According to the breeding habits of snails, from March to November is the breeding season of snails. The eggs of the snails are visible on the mudflats. Therefore, during this period, the snail seedlings can be collected in natural sea areas, but the temperature changes drastically. It has a great influence on the development of embryos in the eggs of the snails, so it is better to use spring seedlings for breeding. Collect seedlings, use common scraper to scrape seedlings in places where seedlings of seedlings are dense, scrape seedlings, and screen the individual size of the collected mud snails. Farming, large-scale breeding can be sold in 1 to 2 months, small-scale breeding takes 3 to 4 months, and general seedlings range from thousands of grains to tens of thousands of grains per kilogram. Winter seeds are bred per kilogram. 20000 to 30,000 grains are good. This type of natural harvested seedlings is greatly affected by natural resources, and has a high annual yield. The number of harvested fruits in the year of non-acquisition is small.
(b) Earthworm breeding seedlings
Turfgrass cultivated seedlings is also called semi-artificial nursery. It is currently the development direction of snail breeding. It has the advantages of high seedling emergence, convenient management, protection of resources, and easy access to seeds. The specific approach is: In August, in the calm sea, the benthic diatom-rich high tide area in the tidal flat surrounding nursery pool, each area of ​​2 to 3 acres, the pool depth of 0.5 to 0.8 meters, water storage capacity of about 0.5 meters, low quality Muddy or sandy. After the dam has been built, it can be disinfected or exposed to sunlight for 7 to 10 days to kill the enemy. Then flat surface coating, storage of 20 to 30 cm, apply the amount of organic fertilizer, the amount of 100 to 150 kg per acre, training benthic diatoms. After half a month, 50 to 60 kilograms of fresh eggs collected by stocking sea areas, or 5 to 10 kilograms per acre of snails, will be stocked for natural spawning, and 12 to 24 hours of dry dew after spawning. Stimulation, rear water cultivation, stop seedlings. At the same time, timely application of appropriate amount of organic fertilizer, breeding and breeding of single-cell algae for feeding larvae. After the larval worms enter the pupa state, they perform normal dew-drying exercises and become larvae in time to evacuate, with a density of 2 to 5 per square centimeter, and strengthen management measures such as prevention of enemy damage and freezing, until the next year 2 to 3 In the month, high-quality seedlings can be obtained for the production of snails.
(c) indoor artificial nursery
The nursery equipment is the same as the indoor artificial seedlings for common shellfish. It stores 10 to 15 egg groups per liter of water, and hatches in still water. The larvae of the snails are fed with small diatoms, chlorella, and golden algae after being filmed, so that the water body The density of algae maintains 1 to 15,000 cells per ml. Changing the water once a day, each time the amount of water is 1/3 to 1/2 of the body of water. After the juvenile enters the pupa state, it maintains a density of 10-20 cells per square centimeter, is fed with Platymonas and benthic diatoms, and changes the water twice a day, changing the water volume every time by 1/2 to 1/3. In the late period, dry 1 to 2 hours a day, supplement benthic diatoms in time, change the sediment in time when the sediment quality is not good, keep the thickness of the mud layer 1 to 2 cm, and fertilize properly, when the young screw is cultivated to a shell length of 0.5 mm When the above can be moved to the outdoor earthen pond cultivation, the density of 2 to 5 per square centimeter, dry dew two times a day, the appropriate fertilizer, until the shell length of 2 to 5 mm can be raised, for the beach into the screw culture.
Third, mud turtle breeding
(a) Aquaculture. Choose calm, smooth flow, soft coating, benthic diatom rich beach, pond, pond area ranging from several acres to more than ten acres, but with 5 to 10 acres is appropriate. The embankment of the pond embankment can be built. Increase about 50 centimeters, ponds up and down water 20 centimeters, flattening the surface before stocking, clearing the predators. The snails are suitable for stocking before 2 to 3 months. The stocking density is 50-100 grains per square meter, and the specifications are 2-30000 grains per kilogram. Dry seeding is required until the screw body dives into the mud and aquaculture is performed.
(B) flat coated culture. Choose smooth flow, soft coating, thicker "oil sludge" in the surface of the tidal flat area, flat coated fence, an area of ​​10 to 20 acres, remove the impurities in the coating, the principle of flat coating is not water, using bamboo or pine piling, Polyethylene net or nylon sand net fence, the net inserts the mud 20 centimeters, the surface is 1 meters high. Seed stocking and management with aquaculture.
(c) The mud turtle is raised. Mud snails growing in natural sea areas have different quality qualities due to their different growth substrates. The mud snails that grow in sediments with large sediment content often contain large amounts of sediment in the stomach and stomach. Commonly called "muddy" seriously affects the quality of mud snails. The use of mud turtles to improve the quality of snails can be improved. The specific method is to select a mudflat, soft coating, and a muddy muddy tidal flat in the middle tide zone to remove impurities, kill the enemy and pests, smooth the mudflat, and move the muddy mud with poor mud quality. Over stocking, breeding density of 30 to 50 tablets per square meter, evenly spread after ebb tide, stocking specifications for the shell height of 1.5 cm snail, after 10 to 30 days of breeding can be listed from the catch. This breeding method starts in March and can raise 5 to 6 baht a year.
IV. Daily management of mud turtle breeding
(a) Manage water well. When the tide is not able to enter the water, it is necessary to store more water in order to prevent excessive dehydration. When exposed to large tides, appropriate exposure time should be given to promote its growth.
(b) against predators. There is less disease of snails, but seabirds, sand crabs, blue crabs and other crabs are very harmful to snails. Nereis and other animals also compete with slugs and affect the growth of snails. Therefore, during the cultivation period, the enemy should be cleared in time, spraying the drug every 15 to 20 days, removing the sand-preserved crabs, blue crabs, and desert silkworms, and properly storing water to prevent seabirds from swallowing. .
(c) Anti-escape. The mud snails kept on the mudflats are often exposed to rain, colder weather, direct sunlight, and windy winds. They often use their heads to dig sand and dig into the surface of sediments. The mud layer is foraging on the mudflat. However, when the muddy or water quality of the cultured land is unfavorable, or the biological feed material is insufficient, the mud snails must migrate collectively. To prevent the mud snails from fleeing, a one-meter-high can be used to coat the mud. Ethylene mesh or improved environment, breeding mud snail bait and other measures to prevent snail escape.
(d) Fertilization. Applying a proper amount of fertilizer can increase the bait of mud snails, which is the "oil sludge" of the cultured mudflats. During the growing season, fertilization is usually conducted once every two weeks, and manure (fermented chicken manure, etc.) is 20-30 kg per mu, and the amount of inorganic fertilizer is used. Each application of 2 kg of nitrogen fertilizer and 0.5 kg of phosphate fertilizer is mixed. The benthic diatoms in the mudflats are reproduced, and organic fertilizers can also be directly added as bait for mud snails.
(five) inspection inspection observation. After nudibranch aquaculture, observe the growth activities of snails on a daily basis to facilitate timely fertilization and detoxification. When seeing migrating plants have signs of migratory movement, they may adopt necessary measures for avoiding escape or transfer culture. Do a good job of routine anti-escape and other work.
(f) Harvest of mud snails. With a proper density and a rich diet, mud snails can be harvested after 1.5 to 3 months of cultivation, reaching 300 to 400 grains/kg. The snails are generally harvested in spring and autumn, commonly known as the yellow-headed snails (Peach flowers) and the sweet-scented osmanthus snails, but the quality is better than that of snails. The catching method uses hand catching or special bulldozing nets to move two catches, and the quality is better to catch by hand.
Bullacter Bullacta exerata Philippi (Figure 4-4), commonly known as spit iron, also known as the snails, plum snails, yellow snails, belongs to the gastropods after the end of the steel head shield A The types of salt water products are widely distributed on the north and south coasts of China, especially in the Ningbo and Zhoushan areas of Zhejiang Province. They are the most important economical shellfish on the northern coast of the province. They are of delicious meat and have high food value, and are deeply loved by people. .