Artificial Insemination Methods and Technical Points for Rainbow Trout

1. Preparation before insemination: Tools: a white porcelain washbasin can be used as the egg-collection and fertilization basin; in addition, medical gauze, feathers, a microscope, beakers, graduated cylinders and other tools are also needed. Preparation of isotonic solution: sodium chloride 90.4 g, potassium chloride 2.4 g, calcium chloride 2.6 g, dissolved in sequence in 10 L of water, and stored above 4°C; its function is to dissolve the yolk protein flowing out of broken eggs so as to increase the eyed-egg rate.

2. Identification of mature broodfish: Fully mature broodfish have a swollen, soft abdomen, with the genital pore red and swollen and protruding outward; when the caudal peduncle is lifted, the ovaries on both sides droop, the ovarian outline is obvious, and eggs flow out when the abdomen is gently squeezed. Mature male fish become darker in body color, with a rough body surface, slightly reduced mucus, and a soft area around the vent; white milt flows out when the abdomen is gently pressed, and disperses upon contact with water. Feeding of the broodfish should be stopped 2-3 days before egg collection and insemination. Mature broodfish should be stripped and inseminated promptly, otherwise fertilization and hatching results will be affected. Generally, check once every 10 days; if the water temperature is slightly higher, check once every 5-6 days.

3. Egg collection and insemination: When collecting eggs, hold the female fish by the caudal peduncle with one hand wrapped in gauze so that the vent points directly at the basin, and gently press the abdomen in front of the vent with the other hand; the mature eggs will then flow out accordingly. The squeezing motion should be light and quick, avoiding injury to the broodfish as much as possible, and it should be carried out under conditions without direct light. After collecting the mature eggs, immediately rinse them with isotonic solution, and at the same time quickly squeeze milt onto the surface of the eggs; generally, the eggs of 5-7 females are fertilized with the milt of 2-3 males. To save milt, the milt may also be stored in a graduated cylinder in advance; at fertilization, use 10 ml of milt per 10,000 eggs, stir with a feather for 30 seconds so that eggs and sperm fully contact each other, then add a small amount of isotonic solution or clean water, and stir evenly and quickly for 1-2 minutes; afterward add a large amount of clean water to wash away excess milt and egg membranes, etc. Finally, add a large amount of clean water, let stand in still water for 30-40 minutes to allow full water absorption, and after swelling, incubation can begin. To improve the fertilization rate, freshly collected eggs must never come into contact with water, and each time eggs are collected, the insemination time should not exceed 2 minutes.