CATDOLL : CATDOLL: What are the detailed steps for hatching grass carp fry?

1) From the hatching of the bridging membrane to the disappearance of the yolk sac, in the late stage of goldfish embryonic development, when the tail fin is formed and the radially arranged fin rays appear, the embryo begins to hatch. The newly hatched fry has a curved body, a large yolk sac, an open mouth, and a transparent body. The myometrium and circulatory organs of the fish can be clearly seen. The gills are only a groove, and the pelvic fins are not very obvious. The newly hatched fry have no swimming ability and can only attach to the fish nest or the wall of the pool or crawl on the bottom of the water. When frightened, they can only move from one place to another like jumping. At this time, the fry cannot absorb food from the outside world and can only survive by absorbing nutrients from the yolk sac. No food needs to be fed during this period. In terms of management, do not tamper with the hatching tank and aquatic plants to prevent the small fry from falling to the bottom of the water and being covered by impurities and dying.

(ii) After about 3 to 5 days, the nutrients in the yolk sac have been completely absorbed, the yolk sac has shrunk, and the fins have developed relatively well. When the fry are still, they no longer lie on their side, but can swim horizontally and no longer cling to objects. The lower jaw has been formed and can move. At this time, the fry have already been looking for food, but because the fish body is too small and moves slowly, they cannot take the initiative to grab food, and can only swallow a small amount of phytoplankton and protozoa. During this period, egg yolk water is generally fed, and one egg yolk can feed 10,000 fry. There are many ways to feed egg yolk water. One method is to mix the cooked egg yolk with water, and sprinkle the egg yolk water around the water plants or the edge of the tank to facilitate the fry to find food; the second method is to wrap the cooked egg yolk with gauze, and then squeeze the gauze wrapped with egg yolk in the water slightly to make the egg yolk water flow into the water. When the belly of the fry is light yellow, it means that they are full and can no longer be fed. Feed 1 to 2 times a day, and the amount should be small. Too much egg yolk will affect the water quality.

(III) About 5 to 7 days after hatching, when the fry are able to swim to the surface of the water, you should start feeding them "grey water" (protists). The "grey water" must be filtered through a fine mesh to prevent large fleas from entering the fish pond. Large fleas should be kept away from the fish pond.

(iv) When the fry are about 1 cm long after one week of growth, they will actively eat. At this time, they can be fed various types of rotifers and "red worms" (cladocerans, never copepods). You can also add some green water from the pond. This green water contains a large amount of microorganisms and algae, which can be used as a supplementary food for the fry. It is very beneficial to the growth and color change of young fish.

Under natural conditions, grass carp cannot spawn in still water. The spawning sites of the grass carp are generally selected at the confluence of the main stream of the river, the deep channel waters on the side of the river bend, and the river sections where the two banks suddenly contract as suitable spawning sites. The reproductive season is similar to that of silver carp, but slightly earlier than that of black carp and bighead carp. The reproductive period is from April to July, and is more concentrated in May. Generally, when the river water rises early and violently, and the water temperature can be stabilized at around 18℃, grass carp spawning will be in full swing. The reproductive habits of grass carp are similar to those of other domestic fish. The ovaries of grass carp that have reached maturity will hibernate in the stage III development stage throughout the winter (December to February); when the water temperature rises to around 15℃ in March and April, the stage III oocytes in the ovaries quickly develop to stage IV and begin reproductive migration. During the upstream migration, the development from stage IV to stage V is completed. If it encounters hydrological conditions suitable for spawning during its upstream migration, it will spawn. Usually, spawning takes place in the water layer, and the fish body does not float on the water surface, which is commonly known as "stifled spawning". However, when encountering good reproductive ecological conditions, such as a sudden rise in water level accompanied by thunderstorms, the male and female fish chase each other in the upper layer of the water, and the "floating row" phenomenon with their abdomens trembling on their backs appears. After the eggs are fertilized, the egg membrane absorbs water and expands, and the egg diameter can reach about 5 mm. It drifts downstream and develops best at around 20℃. The fry hatch in about 30-40 hours.

Grass carp grows rapidly. In terms of the entire growth process, the fastest growth period of body length is 1-2 years old, and the fastest growth period of weight is 2-3 years old. When the 4-year-old fish reaches sexual maturity, the growth slows down significantly. The body length of 1-winter-age fish is about 340 mm and the weight is about 750 grams; the body length of 2-winter-age fish is about 600 mm and the weight is 3.5 kg; the body length of 3-winter-age fish is about 680 mm and the weight is about 5 kg; the body length of 4-winter-age fish is about 740 mm and the weight is about 7 kg; the body length of 5-winter-age fish can reach about 780 mm and the weight is about 7.5 kg; the largest individual can reach about 35 kg.

Grass carp grows fast and is large, with the largest individual reaching 35 kg. The meat is tender and delicious. Every 100 grams of edible part contains 15.5-26.6 grams of protein, 1.4-8.9 grams of fat, 83-187 kcal of calories, 18-160 mg of calcium, 30-312 mg of phosphorus, 0.7-9.3 mg of iron, 0.03 mg of thiamine, 0.17 mg of riboflavin, and 2.2 mg of niacin.

Grass carp is often used as the main stocking object in ponds, lakes, reservoirs and rivers because of its simple diet, wide source of bait, rapid growth and high yield. Since the success of artificial induction of spawning and fertilization and hatching technology in 1958, the source of fry and fish species has been easy, and it has become the main intensive breeding object in my country. Grass carp is also used by fishermen to stock it outside for one or two years to open up wasteland and weed because it can remove grass in the water and along the coast. Grass carp is called "pioneer" because it can quickly remove various grasses in the water. In the late Tang Dynasty in Guangdong, there was a record of building ridges on wasteland, irrigating it with rainwater, and stocking grass carp for one or two years to remove weeds and mature the fields. Grass carp is often mixed with silver carp and bighead carp. Grass carp is fed with green grass ridge pants, and the feed left in the water and the waste discharged by grass carp are used to cultivate plankton as feed for silver carp and bighead carp.

Grass carp is widely distributed in the plains from Guangdong to the northeast of my country, except Xinjiang and the Qinghai-Tibet Plateau. Since the successful artificial induction of fertilization and hatching in 1958, it has been transplanted to many countries in Asia, Europe, America and Africa.

Grass carp meat is sweet, warm and non-toxic. It has the effect of warming the stomach and harmonizing the middle. People in Guangdong use it to steam with fried dough sticks, eggs and pepper powder, which can improve eyesight. Its gallbladder is bitter, cold and poisonous. Animal experiments have shown that grass carp gallbladder has a significant antihypertensive effect, and has expectorant and mild antitussive effects. People in Jiangxi use bile to treat sudden deafness and burns from water and fire. Although gallbladder can cure diseases, it is poisonous. There are often cases of poisoning caused by swallowing too much grass carp gallbladder. The poisoning process is mainly the effect of toxins on the digestive system and urinary system, causing gastrointestinal symptoms, liver and kidney failure in a short period of time, and often accompanied by cardiovascular and nervous system lesions, causing cerebral edema, toxic shock, and even death. There is no specific treatment for those who are poisoned by swallowing grass carp gallbladder, so it is not appropriate to use grass carp gallbladder to treat diseases. If it must be used, it must be used with caution.

In May, the abdomen of the female fish is swollen and soft, and then LRH-9 (oxytocin) is injected. The water temperature is about 25 degrees. The effect time is about 10 hours. Check the reproductive hole of the fish and squeeze the abdomen gently to see eggs flowing out. At this time, the fish eggs should be squeezed out of the plate immediately, and then the male fish's imitation semen is squeezed onto the fish eggs. Use a feather to quickly mix the sperm and eggs evenly. Fertilization is completed in about 20 seconds. Finally, the fertilized eggs are slowly poured into the prepared loop hatching pool. The water flow in the loop pool should not be too fast, and it is better to just disperse and suspend the fertilized eggs. About 3 days later, the fish eggs break the shell, and the small fry are born. After about 48 hours, when the yolk of the fish flower disappears (the belly is closed), the fish flower can be harvested and placed in the fish fry pond for further cultivation.