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Basic conditions and major technologies
1.1 Facilities
There were a total of 10 snails breeding and spawning ponds and nursery ponds with a specification of 3mx6.3mx1.3m, 25m3 per pond water body, 12 hatchling hatchery ponds and bait culture ponds, 5m3 per pond water body. The nursery system is supplied with a 3KW Roots blower. The nursery water is sediment filtered and filtered sand.
1.2 The source of snails and snails was purchased from a trawling fisherboat in Hepuyingpan, Guangxi. Two batches of conch were purchased with 30kg and 40kg, respectively, and their shell height was more than 5cm. Due to the small amount of acquisitions each day, the first-in-a-day acquisition of the conch and cloning will be held at the local nursery farm. After the required number of acquisitions, the conch and snail will be transported back to the test base by means of cooling and dry transportation. The specific transportation method is: Put a plastic tweezers with ice cubes into the foam box (the ice cubes should be sealed with plastic bags to prevent the ice from melting and then soak in the snails), and then place snails and snails around the tweezers. The top is covered with a layer of damp cloth, which can be transported by capping and sealing. The role of the plastic tweezers is to separate the ice from the conch and snail to prevent the snails from being frostbite; each case contains 20kg of snails and snails.
1.3 Cultivation of the snails The orientalis snails of D. piquant have diffusing sand habits. The pronulotidium that was sent back was cultivated in a pool of snails and snails with 5cm sand on the bottom of the pond. Invest in locally available miscellaneous fish and pearl shellfish and feed it once a night. The amount of bait is about 5% to 10% of the body weight of the snails. The specific amount of bait may be adjusted according to the situation of the snails and snails, generally the next day. A small amount of remaining bait is suitable in the morning. Change the water and clean the water every morning from 8:00 to 9:00. First drain the water from the dew pond to eliminate the residual baits at the bottom of the pool. Rinse the bottom sand with seawater and fill it with water. In order to prevent the snails from being washed away at the water outlet plus the isolation net, the sand is disinfected once a week with potassium permanganate at a concentration of (50-100)x10-6.
1.4 The mating and hatching of the snails Maturation The snails will naturally mate and produce oocysts under artificial cultivation conditions. In the case of the common airflies, a number of wedge-shaped oocysts are formed on the sand at the bottom of the pool. Collect the oocysts and change the water. After the water is drained, the oocysts can be collected. The collected oocysts are cleaned, disinfected with 100x10-6 PVP-I for 2 to 5 minutes, and placed in a 40-mesh small cage at the nursery. When hatching in the pool, the bottom of the cage should be leveled as much as possible to prevent the oocysts from being stacked together to cause local hypoxia and affect the hatching rate of the eggs. After about 6 days at 27°C, the larvae hatched. The hatched larvae enter the nursery pool through the cage. The empty oocysts and the unhatched oocysts remain in the hatching cage until the larval density is reached. 10,000 to 20,000/m3 were reached. The oocysts were moved to another pool and continued to hatch.
1.5 Incubation and management of larvae: Change the water every day in the first 5 days, and then change the water twice a day. The total amount of water exchanged per day is 20% to 50%. With the growth of larvae, the nets of different nets of the water changer were replaced, and 100 mesh nets were used during the floating season, and 80 mesh nets were used after the metamorphosis.
Feeding: The planktonic larvae are mainly fed with Chlorella, supplemented by gold algae, Platymonas and baker's yeast. Each day in the morning and in the afternoon, the bait is fed once. The amount of larvae fed at different developmental stages is shown in Table 1.
Water conditions in the incubation period: water temperature 23°C to 29.8°C, seawater relative density 1.021 to 1.023, pH 8.1 to 8.3, and dissolved oxygen >5 mg/L.
1.6 Management of larvae during metamorphosis The larvae have an abnormal ability of 760 μm. At this time, the larvae are transferred to a nursery pond with sand on the bottom of the pool for metamorphosis. The specific method is as follows: The 40-mesh screened sea sand is rinsed with fresh water. , Disinfect with PVP-I 200x106 concentration for 10 min, rinse the liquid and spread evenly to the bottom of a sterile nursery pond. The thickness of the sand is about 0.5cm, and fill with water.
Use a water changing device to drain the nursery pond water with larvae to 30cm to 50cm. Place a seedling cage at the outlet of the nursery pond, and add seawater in the seedling collection tank so that the water level in the tank is 10cm to 20cm lower than the water level in the nursery pond. Pull up the drain plug to drain the larvae to the seedling cage. Keep the water level difference between the seedling collection tank and the nursery pond not too large to control the discharge speed of the larvae and prevent the water from rushing to damage the larvae. The collected larvae are cleaned and transferred to the above prepared nursery ponds.
At this time, the method of feeding the algae is to continuously feed the algae, and then feed a small amount of fish. In order to facilitate observation of metamorphosis of the larvae and timely removal of the residual bait, the fish should be placed on the bait station, and the production of the bait station is shown in FIG. 1 . Feed the fish every day for 1 to 2 hours and lift the bait station to check if any metamorphosed larvae are attached to the fish. Place a bait station every 3 to 4m2.
1.7 Anti-disease measures The antibiotics are administered every 3 days during the floating season. The types of antibiotics are: Baiyanjing, Norfloxacin and Ciprofloxacin. These antibiotics are used in turn at a concentration of 0.5x10-6. Stop changing the water one day after administration.
1.8 Management of juvenile larvae When there is no planktonic larvae in the nursery pond water, the larvae are completely metamorphosed into juvenile snails, and they are stopped feeding algae and only feeding the flesh. The tongue of the newly metamorphosed juvenile screw is still delicate, and is fed with meat that is softer and has been frozen and then thawed.
The juvenile snails have wall climbing habits, and hang double-layer gauze soaked in seawater above the surface of the inner wall of the pool to prevent the juvenile snails from drying out. Each gauze was collected at 7:00 and 18:00, and the juvenile snails in the pool wall were flushed into the nursery water.
1.9 Outlet method of juvenile snail
1.9.1 Screening method Sand and young snails are placed in a 40-mesh screen and sifted in water. The sand sinks to the bottom of the water through the mesh, and the juvenile snail remains in the screen.
1.9.2 The bait trap method stops feeding the bait once so that the juvenile snail is in a proper state of starvation. The fish is then placed on the bait station. The bait station is lifted for about one hour and the young snails attached to the flesh are collected.
2 Results and Analysis
2.1 The mating and spawning of the snails and the ovipositors of the orientalis spirulina are diploid and fertile, belonging to the species of fertilization and ovulation in the body. Male snails have transitional projections below the right antennae, while females do not. Under artificial rearing conditions, male and female can both mature mating and spawning. Normally, the water is exchanged in the morning and the mating activity is performed in the evening. The eggs are laid at night and the eggs produced are packaged in the oocysts. The oocysts are usually produced on the sand at the bottom of the pool. The bases of the long wedge-shaped oocysts produced by each female snail stick together to form an egg group. The number of oocysts per egg group and the number of fertilized eggs per oocyst Differently, 10 egg groups were randomly selected for statistics of spawning. The results are shown in Table 2. It can be seen from Table 2 that the oviposition amount of the oriental arborescens is generally 3.4 to 47,000, and the eggs per oocyst are 670 to 940.
2.2 The relationship between the growth rate of larvae and juvenile snails and water temperature The growth rate of the larvae and juvenile snails of P. bungeana is greatly influenced by the water temperature. The water temperature is high and the growth rate is fast. When the water temperature is low, the growth rate is slowed down. The growth of larvae and juvenile snails in the nursery experiments in 2002 and 2003 are shown in Table 3. It can be seen from Table 3 that when the water temperature is low, the growth rate of larvae slows and the planktonic period increases. In 2002, the floating period was about 33 days. In 2003, the high water temperature floating period was only about 24 days. In the 2002 fish breeding trials, the water temperature in the metamorphosis stage of ponds Nos. 5, 6 and 7 was dropped to 23°C due to cold air. Most of the larvae could not metamorphose and died. The other four ponds were also in a state of stagnant due to the low water temperature. Therefore, the water temperature during the whole nursery period should be above 25°C; in the 2003 experiment, the water temperature during the nursery period of each pond was higher, and the time from juvenile to mature shell height 2mm was only 21 to 23 days.
2.3 Nursery results in 2002 and 2003
From September to November 2002, a total of 78.4 eggs were laid in the nursery trials, with a seedling emergence of 0.94 million/m2; in the nursery trial from May to August 2003, 10 eggs were laid out, and 2.48 million seedlings emerged. An area of ​​13,000 m2 emerged and a very good nursery effect was achieved. Specific test conditions are shown in Table 4.
3 Questions and Discussion
3.1 Feeding Techniques for Metabolic Animal Feed Metamorphosis is the period when larval life habits shift from planktonic to benthic and feeding habits from plant to bait to animal bait. Dongfeng snails are not synchronized in their spawning, which results in unsynchronized development of larvae and inconsistent metamorphosis. Therefore, in the metamorphosis stage of larvae, animal feed should be added on the basis of feeding algae. According to data [1, 2], metamorphosis larvae are fed fish paste or minced fish to meet the feeding needs of metamorphosed larvae. According to the author's observation during the nursery process, the castrated fish larvae can metamorphose into juvenile snails during metamorphosis, but small particles of fish flesh in the fish slurry are suspended in water and cannot be fed by juvenile snails, which can easily pollute water quality; Underwater, can not be completely eaten by juvenile snails clean, there is no way to remove them, easy to contaminate the bottom, the practice of feeding fish paste and minced fish will often lead to deterioration of water quality and sediment, resulting in a large number of deaths of larvae and juvenile snails, Caused low emergence rate.
The individual metamorphosis larvae are larger, the face plate tends to shrink, and the gastropods become more developed. They move on the bottom of the water body and alternately crawl and swim. The author once put the soon-to-be transformed larva into a glass jar, overnight the larvae's face plate fell off, changed from planktonic life to benthic life, and began to actively eat lumpy fish. The metamorphosed larvae have a crawling ability and have a well-developed sense of smell. After feeding the fish, juvenile snails within 1 m from the fish flesh move quickly to the fish. See Table 5 for reaction times of juvenile snails at different distances from the fish.
In the experiment, we used multi-point and fixed-point methods to feed flake-like fish to the bait station. On the one hand, we could fully feed on the juvenile deceased juveniles and check the metamorphosis of the larvae. On the other hand, it is easy to remove the bait and avoid residues. The bait polluted the water and proved to be a reasonable bait feeding method during the metamorphosis period.
3.2 Discussion on the cause of death of juvenile snails and their countermeasures According to the author's observation, juvenile snails have wall climbing habits and often climb above the surface of the pool; juvenile snails have strong gastrocnemius secretions and juvenile snails are lighter. The juvenile snails attached to the pool wall are often stuck to the pool wall even if their gastropods have been retracted. They cannot fall into the water from the pool wall. A long time will cause dry snails to die. July 2003 Experiments were conducted to determine the relationship between the time for juvenile dew exposure and the mortality rate of 1 to 1.2 mm in shell height at different temperatures. The results are shown in Table 6. It can be seen from Table 6 that the higher the temperature is, the shorter the ecological time of juvenile snails in the exposed state.
In the artificial breeding of Dongfengluo in general use of water scoop to water the method of the young screw back into the pool to avoid young snail dying because of the time is too long, but this method requires 30 to 50min splashing once the wall, often because of work If the amount is too large, it can't be sprayed in time and cause a great deal of death of the snails. In the experiment, we used the method of attaching wet gauze to the pool wall to solve the death problem of the young snails. The specific approach was to put double gauze soaked in seawater on the side of the pool wall, and the other side hangs down along the pool wall. When immersed in water, the juvenile snail climbs into the gap between the gauze and the pool wall and cannot climb too high. The viability of the juvenile snail after it was kept wet for 12 hours was 100%. Practice has proved that this method is simple and easy, and it is an important means to improve the survival rate of young snails.
It is a tropical and subtropical species. It is mainly distributed in the coastal areas of Fujian, Guangdong, and Guangxi. It has fast growth and delicious fleshy taste. It is emerging in recent years. A mariculture species. However, over-counterfeiting has greatly reduced the natural resources of E. orientalis, and it needs the artificial breeding of the counterpart P. ostreatus to meet people's needs. Based on previous work, the author conducted two years of artificial breeding trials of E. orientalis at Zhanjiang Ocean University Fighting Test Base in 2002 and 2003, and achieved good results with a seedling yield of 130,000/m2. Report the technical measures and results of the test as follows