Discussion on artificial breeding technology of catfish

I. Materials and methods

1. Test sites and facilities

The original spawning ponds and incubation ponds of common carp and crucian carp and four domestic fish were used in the experiment. Fish nests with palm bark after cooking and disinfection are strung together with bamboo poles or ropes, hanging in the upper and middle layers of the spawning pond, and the bottom of the pond is covered with palm bark.

two。 Source and cultivation of parent fish

Parent fish are mainly collected from wild fish species in Biliuhe Reservoir in Dalian City for intensive cultivation in ponds. Parent fish are cultivated and fed with freshwater mixed fish and mussel meat. The average weight of male fish is 500g / fish and that of female fish is 750g / fish. Bait twice a day and lure food with lights at night. The daily feeding amount is 2% to 5%.

3. Male and female identification and collocation proportion of parent fish

The female and male parent fish are distinguished by the caudal fin fork, the female fish tail fork is shallow, not obvious, while the male fish tail fork is deeper and obvious. The proportion of male and female fish was (2.2-2.1) ∶ 1.

4. Drugs for inducing labor and their dosage

The oxytocin was given with a combination of SGnRH-A (salmon releasing hormone analogue) and DOM (dione maleate) at a dose of 8 μ g + 8 mg / kg body weight.

2. Test results

1. Injection and effect time

Injection using the dorsal fin after the base injection method, the needle facing the head, and the body into a 45-degree needle, the needle depth of about 1.5 cm, slowly push the drug. In order to facilitate injection, parent fish are loaded in transparent plastic bags. The effect time is closely related to water temperature, maturity of parent fish, water flow, types of spawning drugs and injection dose. The suitable water temperature for estrus and spawning is 18: 30 ℃, but 24: 25 ℃ is the best. The time from estrus to spawning is longer, about 2-5 hours, but shortens with the increase of water temperature. Flushing has a certain stimulating effect on the estrus of parent fish, especially for those with poor maturity, increasing the amount of flushing can achieve obvious effect. Usually the parent fish has been in a micro-flow state since the parent fish entered the induction pond, increasing the water flow 1-2 hours before estrus. During estrus, male fish wrap their bodies around the female's abdomen and squeeze each other to spawn and ejaculate.

two。 Incubation

After all the spawning is over, the fish nests and eggs are thoroughly disinfected and transferred to the hatching ring to hatch, where the water is maintained and the bottom is covered with palm bark, so that the fallen eggs will not be dense and suffocate to death. The time of breaking the membrane of fish fry hatching is related to the water temperature, when the water temperature is 17: 23 ℃, the breaking time is 72: 80 hours, the water temperature is 24: 26 ℃, the breaking time is 44: 50 hours, the water temperature is 27: 30 ℃, the breaking time is 24: 40 hours. The newly broken fry is milky white, with a total length of 0.5 cm to 0.6 cm, with a large yolk sac on the abdomen, and fry generally gather around the nest. After that, the pigment on the body surface gradually deposited and appeared gray-black after 3-4 hours, and then the yolk sac basically disappeared, and the tail could be swung horizontally. at this time, we should go to the pond in time according to the specific situation.

3. Result

A total of 409 groups were spawned by artificial breeding, with an average of 11200 eggs per group, 3.18 million eggs obtained, 61.3% fertilization rate, 43.1% hatching rate and 840000 fish fry hatched.

III. Problems and discussion

1. Nutrition problems during parent fish cultivation

In the process of parent fish cultivation, it is very important whether the nutrition of feed can meet the gonadal development. This experiment adopts the method of feeding dead fish, which has many shortcomings: first, some foods can not be used, and the water quality is polluted after decay, which seriously affects the normal life of parent fish in the pond; secondly, regular feeding of single bait, lack of necessary nutritional elements, prone to diseases such as skin rot and fatty liver.

two。 Problems of male and female culture and matching of parent fish

Male and female fish should be cultured in separate ponds, especially when the water temperature rises to 15 ℃. In the breeding season, the maturity of parent fish should be strictly controlled. In this experiment, group reproduction was adopted, and some parent fish that were not fully mature were also induced to lay eggs, thus affecting the total number of eggs laid.

3. The problem of fecundity of parent fish

A total of 3.18 million eggs were obtained in the experiment, with an average of 11200 eggs per group. Although it was relatively high on the whole, it was found that there were not many large individuals in the process of spawning, indicating that the maturity of large individuals was lower than that of some small individuals. Secondly, there is a great gap in the size of male and female individuals, uneven size of male fish, more small individuals, weak chase intensity and the ability to entangle the belly of female fish, which affect the oestrus of female fish. In addition, the injection dose of the drug should be accurately controlled according to the body weight of the parent fish. If the injection dose is low, the spawning and ovulation of the parent fish will be out of sync, resulting in a low fertilization rate.

4. The selection and retention of parent fish

Most of the parent fish used in the experiment were 2-3 winter years old (0.75-1.00 kg / female and 0.30-0.75 kg / male). In the past, the practice of choosing parent fish in the fish fry farm of Biliuhe Reservoir was to return most of the parent fish back to the original pond for re-cultivation after induced spawning. although this can avoid the problem of low fecundity of first-time female fish because the age of parent fish is too low, but long-term cultivation has caused skin diseases, liver diseases and other diseases.

5. Fertilization rate and hatching rate

In this experiment, due to the improper ratio of female to male (more female and less male), and the shedding and sinking of most eggs, the fertilization rate of eggs was affected. At the same time, most of the bottom eggs died in the process of hatching due to high density and low flow. Water pollution caused the death of some hatched fish fry.

6. Several measures to improve breeding techniques

The main results are as follows: (1) to strengthen the cultivation of parent fish, it is best to use special pellet compound feed for catfish, which has the advantages of comprehensive nutrition and convenient storage and transportation. During the cultivation period, attention should be paid to the inspection of the maturity of parent fish in order to adjust the cultivation method in time. In the reserve of parent fish in batches, different breeding measures should be carried out according to different ages, different individual sizes, newly selected or original ponds, those to be laid for the first time or those who have participated in spawning. Male and female fish are strictly cultured in separate ponds in early spring or about a month before spawning, so as to avoid sporadic natural spawning in the breeding season.

(2) accurate identification of maturity and rational matching if natural reproduction is adopted after induced spawning, the maturity should be accurately identified and the proportion of male fish should be increased, and the female-to-male ratio can be increased to 2 ∶ 3 or 3 ∶ 5, especially when the individual size difference between male and female fish should be taken into account. The minimum size of male fish participating in breeding is 0.5 kg / tail. It is recommended to use more than 3-year-old male parent fish and cultivate them with nutritious and comprehensive feed, which can not only ensure a higher number of eggs, but also increase the number of spawning and spawning.

(3) to accurately determine the drug of inducing labor and the injection dose, the mixed injection of SGnRH-An and DOM can induce the birth rate of more than 85% if the maturity of catfish is good. This method has obvious advantages compared with the previous use of LRH-A plus DOM or LRH-A plus pituitary or HCG (chorionic gonadotropin). When determining the injection volume of the drug to induce labor, weigh each fish as much as possible in order to accurately calculate the drug dose.

(4) the unglued hatched catfish eggs are sticky eggs, which can be hatched by running water through drug de-sticking. The hatching effect is shorter, the hatching rate is higher and the fish fry are physically strong than those hatched with the fish nest. however, the selection of de-sticking methods needs further experiments.