1. The choice of broodstock
The choice of good or bad broodstock is the key to the success of artificial breeding. To select 2-year-old mature broodstock, place the male and female broodstock in the spawning pond on a 1:1 basis. Mature females have a lighter body color, less mucus on the body surface, and a pronounced roughness in the hand membrane; a plump abdomen with a distinct ovarian contour; a slightly enlarged external reproductive process that is reddish, a wide base, a deep degree of freeness, and a fan-shaped appearance of the external genital process; a larger cloacali, located at the sub-terminal of the reproductive process, slightly raised on both sides, without melanin spots. Mature males have darker body color, more obvious markings, more mucus on the body surface, smoother hand touch; the abdomen is not obviously plump; the external genital process is much smaller than the female, showing a white triangle; the cloacatomy is open at the very end, and there are a few melanin spots around the hole.
2. Induce spawning
The oxytocin and dose is females (75-100 g of body weight), 1 pituitary gland (approximately 3 mg weight) plus 700 IU of chorionic gonadotropin (HCG) per carp, and the induction injection is a single injection. The injected broodstock are placed in spawning tanks with cave dwelling and ovarian foci in a ratio of female: male = 1:1. Nests for burrowing and egg laying are made of tiles or planks. The nest is about 30 cm wide and about 20 cm high. The depth of the spawning pond is 40 cm. The water of the spawning pond is purified tap water. After the injection of broodstock into the pond, they will choose their own nest and pair themselves, and after about 24-48 hours, they will lay their own eggs in the nest; the resulting pieces will attach to the nest wall. The success rate of inducing labor is about 70%.
3. Artificial incubation
After spawning, planks or tiles (egg attachments) with fish eggs attached to them can be moved to a pool with clean water to hatch. At this time, the appropriate density can be controlled according to the incubation pond conditions and according to the seedling method. At a water temperature of 27-32 ° C, the incubation time of fertilized eggs is about 84-108 hours, and the hatching rate is about 80%.
4. Seedling cultivation
The hatchlings are 2.3–2.6 mm long, transparent, and have a large yolk sac on the abdomen with multiple scattered droplets of small lipids on the front of the yolk sac. The fish sink to the bottom of the water and do intermittent spirals up and down from time to time. The juveniles after two days of hatching are 3.2-3.4 mm long. The yolk sac becomes oblong-oval, and the scattered droplets of small lipid droplets in the yolk sac converge into a single large oil ball, located in front of the yolk sac. The digestive tract begins to differentiate, the fovea, intestinal canal, and anus appear, the eyeball begins to be filled with melanin; the odd fin folds further develop and expand, and the baby fish can do rapid up and down swimming. Four days after hatching the membrane, the fry, most of the yolk sac is absorbed, only a small part of the anterior upper part and the oil ball remain, the upper and lower jaws differentiate and can be opened, and the intestinal canal appears segmented. At this time, the fish can do horizontal swimming and foraging food, and can start feeding food.
At this time, the juvenile fish is moved to a cement pond with a capacity of 50 tons, and it takes about a month to breed to a 1 cm size, and the survival rate at this stage is about 20% on average. The body length of 1-3 cm is placed in a cement tank with a capacity of 60 tons, and the survival rate at this stage is 80-90%. The cement ponds for raising juvenile fish should be shaded by one-third of the light, and the stocking density is 5000-6000 fish per pond.
Juvenile fish that reach a size of 3 cm should be transferred to an intermediate nursery earthen pond for cultivation, and after about 2-3 months of rearing, they can reach the size of 7-8 cm of seedlings for sale. The survival rate at this stage is 60-70%, and some individuals reach the 100 g specification.
The key to the survival rate of fry breeding is feed, followed by fine management. About 3 days after the gobies hatch, the yolk digestion begins to feed. At this time, the opening caliber of the juvenile fish is only 100-200 microns. The bait for the opening is: the raw eggs are stirred thoroughly, then about 150cc of hot water is poured into it, filtered with a 100 mesh biological mesh, and then fed. Eggs and plankton are fed three times a day from the second day onwards. By day 15, 60-90 micron plankton (rotifers) are fed. Or switch to a mixture of egg yolks and filtered water fleas or shake mosquito larvae. Due to the weakness of the fry, it should be fed in time and in parts several times a day to ensure the needs of the juvenile fish.
From days 16 to 30, freshwater shoots are fed three times a day. Later, it can be fed surimi, branches, rotifers, etc. made of marine trash fish.
In the process of seedling raising, we should pay attention to changes in water quality, often remove dirt and replace new water in a timely manner, in order to obtain a high survival rate. Fry that have been bred for 10-15 days can reach 5-6 mm in length, and their fins begin to appear, and their swimming ability is enhanced. The juvenile fish mainly feed on fleas and aquatic insect larvae in the water, and the gills are also well developed and can be transferred to large ponds for the cultivation of fish species.