The genus Lateolabrax Japonicus belongs to the order Acridionidae, Acrididae, and Eucalyptus, which are mainly distributed on the coasts of China, North Korea, and Japan. Since the 1990s, flower buds have become one of the main fishes for sea cage culture in China.
Broodstock breeding is the basis of artificial breeding, but also the difficulty of artificial propagation of calyx. Broodstock breeding is generally carried out in sea cages or seawater ponds. According to the gonad development law of the calyx, stage II gonads are wintering period, winter and summer after spring and summer to strengthen cultivation, can make the gonadal development into the phase III quickly and transition to phase IV quickly, laying the foundation for the development of autumn gonadal maturity If the measures are not timely and the gonadal development is lagging behind, it is still in the stage II or the beginning of stage III.
Therefore, according to the law of sexual development of gonads, broodstock breeding should grasp four technical links - "winter protection, spring fertilizer, summer education, Qiu Fan". 1 In the winter, the broodstock that are about to lay eggs should be protected to avoid injuries; the brooders who have laid the eggs should be given extra care to make them safe for the winter; when the water temperature is above 6°C, a small amount of feed should be fed to enhance their physique; 2 After winter, The broodstock’s constitution is weak, and as the water temperature rises, the amount of bait is gradually increased to increase the fatness of the broodstock. 3 The water temperature in the summer is high and the feeding of the broodstock is reduced. At this time, the critical period of gonadal development (from Phase II to Tian During the transitional period, therefore, it is necessary to invest in nutritious foods rich in n-3HUFA, such as oysters, live sandworms, and fresh scads, and adjust the feeding amount in time according to the feeding conditions. 4 In autumn and winter, the breeding season of broodstock, except In addition to normal aquaculture management, special attention should be paid to observing changes in food intake and body shape. Artificial ovulation can only be performed when the gonad develops to the middle and end of the IV period.
In addition, taking into account the growth advantages of wild salmon in the North, nursery units are best to breed native juveniles from the North Sea as the original species, and to select individuals with robust physique, excellent body shape and color, and typical biological characteristics in ponds. Or cages carefully reared, enhanced cultivation, as a broodstock better breeding fry.
2. timely production
Appropriate timing for ovulation should be maturation of the ovary, growth and maturation of the primary oocyte (up to IV+++ phase), nuclear dominance towards the animal pole, and primary oocytes at this stage can receive endogenous or exogenous gonadotropins. Induction of hormones, mature divisions develop into secondary oocytes (ie, eggs). The timing of inducing production in nursery production can be determined according to the degree of female abdomen swelling and observation of digging. If the abdomen enlargement of the female is obvious, soft pressure is exerted on the soft-pressure fish abdomen, and the egg diameter is observed over 600 μm after digging, and the oocyte is observed under a microscope. The nucleus has been deviated. At this time, hormone injection can achieve a more satisfactory oxytocin effect. If the egg diameter is below 500 μm, hormone production can not be successfully achieved; male fish can squeeze milk abdomen can flow out milk white semen, the oxytocin effect is better.
3. Reasonably select oxytocin and determine oxytocin
There are no uniform specifications for the type of oxytocin induced by the calyx, which is generally used in the production of fish pituitary, synthetic hormones and gonadotropin products. Taking into account the availability of hormones in the production, general commercial preparations LHRH-A3 and HCG are used. LHRH-A3 can induce fish ovulation and sperm production and maturation, its efficacy is more durable, safe and easy to use. It is currently the ideal anaesthetic hormone for promoting ripening. The injection of HCG into fish can promote sexual function and has the effect of promoting the ovulation and rowing of broodstock. It is an efficient oxytocin. The oxytocin doses of the two hormones are generally LHRH-A32-5 μg/kg for females and 700-1500 IU/kg for HCG. Mixing or single use can achieve better oxytocin production effects; the male dose is halved or 1/3. In actual use, the use dose of hormone is determined according to the gonad maturation degree and the experience of nursery technology. The hormone is injected once or several times. The hormone of each injection is dissolved in 1 mL to 2 mL of distilled water for thoracic cavity, intraperitoneal or intramuscular injection. .
To cultivate broodstock with well-developed gonads, it is a good way to obtain high-quality fertilized eggs by means of a small number of injections, small doses, or no hormone injections to achieve natural spawning of broodstock under certain stream stimulation.
4. Measures to improve the survival rate of artificial nursery
4.1 According to the nutritional needs of juvenile and juvenile fry, feeding a full-fledged bait. Babies, juvenile fish fry have higher demand for EPA and DHA. Larvae and Artemia nauplii were mainly fed at the larval stage. The rotifers and Artemias without nutrition enhancement had low EPA and DHA content and could not meet the nutritional needs of larvae. The survival rate of larvae was low and the malformation rate was high. Therefore, rotifers and Artemia must be fortified prior to feeding. The nutritional enhancement agent 50DE microcapsules developed by the Institute of Oceanography of Shandong Province, China, were used to recuperate the aphids. ?
Cauliflower has been able to ingest marine copepods from the late larval stage to the juvenile stage, and has a high content of EPA and DHA in marine copepods, which can meet the nutritional needs of the early stages of larval and juvenile fishery. Therefore, conditional nursery is available. Units should feed marine copepods from the late larvae on a timely basis (best for live animals). In addition to feeding copepods, the juveniles should also be fed with fresh fish gizzards or fed nutritionally complete compound feeds. In this way, the nutritional needs of juvenile fish seedlings can be guaranteed and the survival rate of seedlings can be improved.
4.2 Grasp the right culture. The density of cultivation is one of the main factors affecting the growth rate and survival rate of fry. During the larvae period, the fry should be properly bred in order to improve the utilization rate of the feed, save energy, and reduce the labor intensity; as the fry grows, it should be divided into pools to reduce the cultivation density. The suitable cultivation density is shown in Table 1.
Table 1 Suitable cultivation densities of fry
│Fry length /cm │<1.0 │1.0～1.5│1.5～2.0│2.0～2.5│2.5～3.0
│ Density/Million*mE-3│1.0～1.5│0.5～0.8│0.3～0.5│0.2～0.3│0.1～0.2
The whole cultivation process of fry is divided at least 2 to 3 times. Common pooling methods include adjacent pool siphonage, nighttime light trapping, and fixed-point food trapping (for fish fry over 2.0cm in length).
4.3 The suitable water environment factors regulating the growth and development of juvenile fish in the nursery pond are: water temperature 16°C～18°C, salinity 19‰28‰, pH7.8～8.6, NH3-N<0.02mg/L, Dissolved oxygen> 5mg/L, light <3000LX. During the entire nursery process, the water quality of the nursery pool is controlled through the control of water addition, the bottom of the pool, the removal of dirt from the surface of the pool, and the adjustment of the amount of aeration to provide a good pool environment for the growth and development of the juvenile flower.
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