First, materials and methods
1. Broodstock breeding and selection
(1) Cultivation ponds. The cultivation pond covers an area of ​​8 acres, all of which are rectangular plastic greenhouses from east to west. The bottom sludge is 10 to 15 centimeters deep, the pool is 2.0 meters deep, and the water depth is 1.2 meters. Before the stocking, dry lime is used to clean the pond, and lime is used for 100-150 kg/mu.
(2) Source of broodstock. The broodstock is a sturgeon that breeds and breeds for 2 to 8 years and weighs 1.0 to 4.0 kilograms. A total of 875 tails, including 575 females and 300 males.
(3) Feeding and management of broodstock. The broodstock was put into the cultivation pond on February 20th, stocking density was 50-80 tails/mu, water depth was 1.2 meters, and the concentrate feed (malt, grain buds, cakes, etc.) was fed 1 to 2 times a day. The amount of fish fed was fish. 5% to 10% of body weight. After 30 days of intensive cultivation, gonads develop well.
(4) broodstock selection. The broodstock was selected from 1-3 kg individuals with well-developed individuals with no injury, smooth body surface and normal activities. The abdomen of the female is large and soft, and there is a clear outline of the ovary when looking upwards, and the hand feels elastic. Male abdomen was significantly smaller than females (Table 1).
Table 1 Identification of male and female broodstock during reproductive season
Sex | Body | Abdomen | Chest pelvis | Germ hole
Female | Back high, wide body, small head | When mature, inflated, soft, rounded, circular | Pectoral fins with or without few stars (chasing stars) | Anus and genital holes slightly swollen, bulging
Male | body narrow, long head, large | mature semen with light pressure outflow | chest and pelvic fins covered with beads star, hand touch has a rough feeling | anus, reproductive hole slightly concave, redness, light pressure abdomen with semen outflow, reproductive hole Smaller
2. Artificial oxytocin and hatching
(1) Artificial oxytocin production. The urine production basin is a standard cement pool of 3.8 meters, 3.1 meters and 1.2 meters with a water depth of 50 to 60 centimeters. The source of the water is the Yellow River water, which uses aeration to increase oxygen, heat to adjust the temperature, and the water temperature during the breeding period is 22 to 26°C.
The oxytocologist used dom+lrh-a2 and took one injection of body cavity. The injection dose was (3 mg dom+10 micrograms of lrh-a2)/kg (the oxytocin dose was calculated per kilogram of female fish, and the male fish was halved). The injection method was to push the needle toward The inside of the pectoral fins of the fish is inserted into the body cavity at a 45 to 60 degree angle with the surface of the fish body. The liquid is slowly injected and the needle cannot be penetrated too deeply (approximately 0.8 to 1.0 cm), so as to avoid stabbing the internal organs.
(2) Artificial insemination. Using dry insemination, the estrus is climaxed to the broodstock that is expected to be oviposited. One person clings to the fish, heads up and down and presses down on the genital hole (to prevent eggs from flowing into the water), and the other holds the tail shank and uses it. Towels dry the belly of the fish and then gently squeeze the abdomen (sequentially, rearwardly) by hand to allow the eggs to flow into pre-prepared porcelain basins (be careful not to bring in water, because the eggs are inflated after water is fertilized) Reduce the rate), and then squeeze the male fish on the eggs, stir evenly for about 1 minute by hand, so that all eggs fertilized. This repeats until the eggs are picked up. At the same time, egg collection is estimated based on the egg weight. (Each ovary is placed on an electronic balance, and the weight of each added egg can be known from the weight gain).
(3) Detackification, running water hatching. First mix the fine mud and water into muddy water, filter it with a thin-eye cage (40 meshes), concentrate it like rice soup, pour it into a large porcelain basin, and then one person turns the mud water with both hands, and the other person will The fertilized egg is poured into the hands, placed in the muddy water to oscillate a few times, and the eggs are spread out in the muddy water to stick. After the eggs are completely spread, continue turning the water for 1 to 2 minutes. Then pour the mud water into the cage along with the fertilized eggs. Wash the mud with clean water, sieve out the eggs and put in 1/1500 methylene blue solution for half a minute. After the number is put into the hatching loop water flow hatch. About 800,000 eggs can be laid per cubic meter of water, and the flow rate is a slight degree of rotation of the eggs. During the incubation process, 100 eggs were retrieved from the ring to check the fertilization rate. After larvae are hatched, the hatching rate is calculated based on the number of samples taken.
3. Artificial seedlings
(1) Pre-cultivation. Before the fish was put into the pond, it was put into dry pond water and clear pond (using 115 kg/mu quicklime). About 10 days before the fish is in the pond, the water injection is 50 to 70 centimeters. When the water is injected, gauze filters are used to prevent aquatic insects, wild fish, and sword leeches from entering the pond. In order to fertilize the submerged ponds, 305 kg/mu of livestock manure was fermented in the week prior to the release of fish fry. One week later, the water became brown and the stock was released. The stocking density was 120,000 to 150,000/mu.
(2) incubation period. After 5 to 6 days of hatching fry, the newly hatched larvae have a total length of 3.2 to 4.3 mm. The body is curved, and the yolk sac is large and pear-shaped. Normal side of the ring road edge. After 2 to 3 days of incubation, you can swim and start feeding. You should first feed the cooked egg yolk (100,000 oysters and one egg yolk). Some of them are sold as sprays, and some of them are cultivated in lower ponds. After the pond is gradually added water depth to about 1.5 meters, using fertilizer and soy milk comprehensive feeding method. An average of 3 to 4 kilograms of soy milk is fed daily, which is increased to 5 to 6 kilograms a week or adjusted according to the water color. Take larvae regularly for inspection to prevent pests and diseases.
Second, the test results
1. Breeding effect
In this experiment, 875 broodstock and 575 females were reared, of which 114 were semi-produce and the rest were all productive. The egg production rate was 80.18%. The effective fertility (fecundity/whole body weight) was 49/g body weight.
2. Hatching rate
A total of 3 batches of oxytocin were produced during the entire period of early bloom, and 509.10 million larvae were hatched. Multiple hatching results showed that the hatching rate of the second batch compared to the first and third batches of tests decreased by 15.38% and 7.18%, respectively. This is because after the first incubation and the second incubation, the hatching enzyme produced by the eggs in the loop did not completely disappear, causing a small number of eggs to prematurely rupture the membrane.
3. Fry breeding survival rate
A total of 9.79 million fishes with a body length of 19.87 mm were bred in three trials, of which more than 3 million were over 24 mm in size. The survival rate of the flower was 95.7% and the survival rate of Wuzi was 35%.
Third, discuss
1. The results of this experiment show that it is feasible to use idling plastic greenhouses to cultivate broodstock and adopt artificial temperature-increasing production and incubation to carry out early propagation of puffer fish in the north. Plastic sheds can reach the appropriate urine production temperature (above 15°C) at the end of March, which will allow the production time to be more than 20 days ahead of natural conditions. Umbilical seedlings also come out of the pond 20 days in advance, no later than the south or slightly earlier than the south. It has been reported that the early seedlings of squid feeding increased production by about 20% compared with late seedlings. Therefore, the early production of fry can bring certain economic benefits to the trout farming in Ningxia.
2. According to the forecast of early spring gas changes in Ningxia, this experiment uses the weather changes before and after cold current to correctly grasp the timing of oyster production and hatching, and obtained good results. Therefore, grasping the opportunity to adopt mature eggs at the right time is the key to improving the fertility rate. In addition, water temperature and water flow are important influencing factors for carp spawning under pond conditions. If the water temperature is suitable (above 16°C), under the condition of mixed male and female breeding, once the water is suddenly flushed into fresh water, self-production phenomenon will occur immediately. Therefore, it is forbidden to fill water in the pool within half a month before the birth. In this experiment, the water temperature and flow control of the broodstock reached a better range, so no self-production phenomenon occurred during the whole process, and the amount of eggs obtained was guaranteed.
3. Disease prevention and control is an important part of the whole production process. During the incubation process, we focused on the prevention of saprophytic diseases, and improved the hatching rate and the survival rate of larvae (spring water temperature is lower than 22°C, which is conducive to the occurrence of aquatic mold disease). The following measures can effectively prevent the occurrence of watery mildew: For freshly shed larvae, use 1/1500 methylene blue water-soluble bay to disinfect promptly and separate the larvae from the egg membrane, dead seedlings and sundries.
4. Early fry due to more cold current in early May in Ningxia area, the pool water temperature dropped to 14°C, and the survival rate of conventional ponds in early mature crops was very low. In this experiment, the seedlings were exposed to low temperatures several times, and the size of the fingerlings was restricted in the current year. It is imperative that the ponds in the early-blooming seedlings shed. It is necessary to build a certain size of sheds for the early seedlings to grow in the conditional fishery.
5. The spawning volume measured in this test is low, especially the second batch and the third batch. Mainly because the second batch of broodstock is young, the first time spawning, reproductive function is not strong enough, the amount of fecundity, egg production is not high, and the egg is small, the third batch of broodstock is produced, older, so The breeding of squid is best for broodstock of 2 to 6 years of age, and broodstock breeding work must be done. According to the broodstock breeding situation and the water temperature record, the broodstock is provided with 32% of the crude protein compound feed, which is sufficient to make the inbred mature and mature, and its fertility is equivalent to the squid in the natural waters of South China.
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