The breeding season for mandarin is from mid-May to early June in china's Yangtze River Basin, from April to August in South China, and from mid-June to late July in the Heilongjiang River Basin. Under natural conditions, mandarin fish spawning grounds are usually inlets of lakes with a certain flow rate and shore beaches with wind and waves, and spawning activities are most abundant at night when the water rises after rain. The mandarin fish spawning grounds of Poyang Lake are distributed in the coastal area between the lake mouth and Xingzi, with a water depth of 1 to 2 meters, a flow rate of 0.6 to 0.8 m/s, a sandy bottom, and a water temperature of about 23 °C. Before spawning, mandarin broodstock exhibit swarm characteristics, and when spawning, sexually mature mandarin fish swim in pairs and chase, and then spawn and sperm in batches in the lower layers of the water body. [4]
Mandarin fish are usually 1 to 2 years old males, females are sexually mature at 2 to 3 years, the smallest mature males are 190 mm, 160 g, and females are 200 mm, 160 g. The amount of eggs carried by mandarin fish is related to age and individual size, generally 2 to 3 years old mandarin fish egg carrying, Gucheng Lake 53,000 to 320,000 grains, Hongze Lake 56 to 621,000 grains, Honghu Lake 28,000 to 214,000 grains, Heilongjiang 55 to 469,000 grains. Mature female mandarin ovaries overwinter in Phase III until April when they turn into Stage IV. In The annual change of the average maturity coefficient of Mandarin fish in Liangzi Lake is 0.8 to 9.3 per month, and in April and May, the ovaries have developed to the ivory or IV stage, when the maturity coefficient is as high as 12.5. From June to July, mandarin fish are in full spawning, and the maturity coefficient decreases significantly, about 3.0. From August to November, mandarin mandarin is in the fattening period after spawning, and the ovaries develop from stage VI to II to III. stage, and their maturity coefficient is 0.9 to 4.3. The maturity coefficient of gonadal development during spawning period of Heilongjiang mandarin fish was 3.23-11.2, with an average of 5.58±1.93, and the maturity coefficient after spawning was 0.87-2.32, with an average of 1.60; the maturity coefficient of male fish during spawning was 1.71-2.69, with an average of 2.12±0.38, and the maturity coefficient after breeding dropped to 0.71. [4]
Artificial breeding of mandarin fish should be selected for healthy physique, no disease and no injury. Due to the different conditions of the researchers, the size and age of the broodstock are different, but the female fish are generally required to be more than 2 years old and weigh 1 to 3 kg, and the male fish are 2 years old and weigh 0.75 to 2 kg. Mature females used as artificial induction have enlarged abdomens with a pronounced ovarian contour, a soft and elastic abdomen under light pressure, a lower midipartum, a loose reproductive foramen, and an ovarian contour that can be seen in the elevated tail. Slowly insert the genital hole with an egg digger, dig out a small number of eggs, and soak in the transparent liquid for 2 to 3 minutes to clearly see the white egg nuclei. If the egg nucleus is displaced, it indicates that the gonads have developed into the middle of the IV. period to the end of the IV. period, at which time a higher induction rate can be obtained. Mature males, around the genital foramen are reddish, lightly pressed abdomen has a thicker milky white semen flowing out, into the water to disperse. Mandarin fish fertilized eggs are pale yellow, spherical, with a weak viscosity, diameter of 1.2 to 1.4 mm, the end of the yellow egg, the egg has a large oil ball with a diameter of 0.43 to 0.55 mm, and some have several small oil balls with a diameter of about 0.1 mm. After absorbing water, the egg expands, the space around the egg expands, and when the swelling reaches its maximum, the diameter of the egg can reach 1.7 to 2.3 mm. The specific gravity of the fertilized egg is slightly greater than that of water, sinking in the still water state, and floating in the flowing water, and the egg membrane is transparent and elastic. [4]
The cleft pattern of the fertilized eggs of mandarin is similar to that of other teleost fish, which is a discoid cleft, and the embryonic development process can be divided into 6 stages. Zheng Minquan and others. The main biological characteristics of the six stages of mandarin fish embryonic development were observed under the condition of water temperature 20~25.5 °C. (1) Fertilized eggs. 40 minutes after fertilization, the protoplasm in the egg moves and concentrates towards the animal pole, gradually forming a raised placenta on the surface of the yolk. (2) Ovulation stage. 1 hour after fertilization, a fissure is generated in the center of the top of the placenta and gradually deepens to form a division groove, as the division groove stretches to both sides, deepens, divides the placenta into two, forms 2 division balls of similar size, and enters the 2-cell phase; 1 hour and 20 minutes after fertilization, a division groove perpendicular to the first fissure appears in the center of the two cells of the placenta, forming 4 divisional balls of similar size, entering the 4-cell stage; 1 hour and 40 minutes after fertilization, the third ovation is carried out. Two divisional grooves located on both sides of and parallel to the first divisional groove appeared, dividing the placenta into 8 cells, a total of two rows, 4 in each row, for the 8-cell stage; 2 hours after fertilization, the fourth ovation was completed, and two division grooves parallel to the second ovation appeared, and the 4 cells in each row were cleaved, resulting in a square arrangement; 2 hours and 25 minutes after fertilization, the placenta appeared 4 division grooves parallel to the third ovation, and the fifth ovation was completed, forming 32 cells. At this time, the cell size is inconsistent and the arrangement is not neat; 3 hours and 55 minutes after fertilization, with the increase in the number of egg cracks and the acceleration of the rate of egg cracking, the cells on the placenta become smaller and smaller, multi-layered unplanned arrangement, and enter the multicellular stage. (3) Blastocyst stage. 5 hours and 5 minutes after fertilization, due to the continuous process of egg splitting, the dividing cells become smaller and enter the early blastocyst stage, when many dividing cells are piled up at the original placenta into a high-cap-like protruding blastocyst, the height of which is about 1/4 of the egg diameter; 6 hours and 45 minutes after fertilization, the cells continue to divide, their boundaries are blurred, and the germ layer expands in the direction of the plant pole below, so that the germ layer height decreases, only about 1/6 of the egg diameter, flattened and low-cap covered on the yolk. (4) The embryonic stage of the protozoum. 8 hours and 45 minutes after fertilization, the placenta to the plant pole under the envelope, expansion, when the next bag reaches about 1/4 to 1/3 of the egg diameter, the embryo ring is faintly visible, into the early stage of the protointestinal tract; 11 hours after fertilization, the germ layer continues to be wrapped down, inner coiled, when the current package reaches 1/2 to 3/5 of the egg diameter, the embryo ring is obvious, the embryo shield appears, which is the middle of the prosthetic intestine; 12 hours and 45 minutes after fertilization, the subectroderm package reaches 3/5 to 3/4, due to the results of intracellular rolling, concentration, and stretching, so that the embryo shield is continuously extended and the embryonic body prototype appears. Enter the late stage of the original intestine. (5) Neuroembryonic stage. 14 hours and 30 minutes after fertilization, the sub-germ layer is about 5/6 of the egg diameter, most of the yolk of the plant pole is surrounded, only a small part of the end is exposed, forming a yolk plug, at this time the nerve groove appears in the center of the back of the embryonic shield, the front end of the embryo shield is slightly expanded, and the follicle will be formed later. 15 hours and 40 minutes after fertilization, the yolk has been completely surrounded, the embryonic hole is completely closed, the lower bag is over, and the embryonic body is raised on the surface of the yolk sphere, but the body segment has not yet emerged