Seedling production of barracuda

The seedling production of mullet includes two steps: artificial propagation and seedling breeding. The former is divided into parent fish cultivation, induced spawning (artificially induced ovulation), artificial insemination, artificial hatching and other processes, while the latter is divided into two processes: fry cultivation and fingerling cultivation.

In the study of artificial reproduction of grey mullet, the first artificial spawning of grey mullet was completed in Italy as early as 1930. It was not until the past 10 or 20 years that it attracted the attention of relevant countries in the world, and became an important topic in international biological research. China, the United States, India, the former Soviet Union, Japan and Israel have actively carried out a large number of experimental studies and made great progress. The seedling production technology has reached the production level, and there are still many theoretical problems and technical keys, which need to be further studied and discussed.

First, parent fish cultivation

The cultivation of high-quality parent fish for spawning is the primary key to the artificial propagation of mullet and shuttle, and it is also the material basis and premise of the whole process of artificial reproduction. Only on the basis of the full maturity of the gonads of parent fish, supplemented by appropriate measures to induce labor, artificial reproduction can achieve the desired goal. The role of oxytocin is only to stimulate the ovary to promote egg ball maturation and division, follicle rupture, ovulation and a series of reactions. Whether this series of reactions can occur depends on whether the ovaries can accept this kind of stimulation, that is, the internal cause of the mature state of the ovaries at the time of labor. Practice has proved that only the ovaries at the end of Ⅳ, after a certain water temperature stimulation, can enter the sensitive period and accept this kind of external stimulation. If the parent fish are not well cultivated, the gonads are not yet mature, or if they do not enter the sensitive period, even the best techniques for inducing labor (with high efficiency and large doses of oxytocin) will not help, or it is not ideal. It can be seen that parent fish cultivation plays an important role in the process of artificial reproduction.

To cultivate parent fish is to create good conditions according to the law of gonadal development of mullet and barracuda so as to promote their gonadal development and maturity.

(1) parent fish culture ponds

1. There are no special requirements for parent fish culture ponds, but in order to facilitate the growth, development, feeding and management of parent fish, attention should be paid as far as possible when selecting culture ponds: close to water sources, seawater and fresh water are convenient to discharge, water salinity can be adjusted and pond water quality can be improved at any time; close to the spawning base, the environment is quiet and convenient for transportation, feeding and management. The area of 2-3 mu rectangular fish pond is suitable, if the area is too large, the management is not convenient, fishing is also difficult, and there are many big fish in the pond, which leads to multiple nets in a pond, which is easy to damage the parent fish and degenerate the gonads of the parent fish. The water depth is about 1.5m, the bottom is flat, the slope ratio of the pond is 1: 2.5-3, and the bottom should have an appropriate amount of (5-10cm) mud layer, which is beneficial to breeding basic bait and fishing operation.

two。 The cleaning and cleaning of the parent fish culture pond should be carried out once a year to remove harmful animals, bacteria and some aquatic plants, dig out too much sludge, improve the water quality, and do a good job in the renovation of the pond embankment. Cleaning is usually carried out after the end of artificial reproduction. Before the parent fish is released, fish rattan essence, drifting powder, tea seed cake, ammonia, quicklime and other drugs are used to clear the pond (the drug dosage can be referred to the shrimp pond). Then the sea water was filtered with a 30-40 mesh sieve net and basic fertilizer (chemical fertilizer or manure) was applied to reproduce basic bait for parent fish. Can also first dry the pond water, remove wild fish, apply organic fertilizer, after exposure for 3-5 days, into the water and fertilizer pool.

(2) Origin and stocking of parent fish

1. Parent fish at present, there are three sources of parent fish used for artificial reproduction: first, natural parent fish are collected from the sea in autumn or early spring to promote their maturity after short-term intensive cultivation (such as Shandong, Liaoning and other places). The second is to select individuals artificially cultured in brackish water with a salinity of more than 5% and develop into mature parent fish (such as Tianjin and Hebei) after intensive cultivation in a special pond for one year. Third, in late autumn or early spring, cultured barracuda selected from fresh or brackish water (salinity 0.5-5.0 ‰) gradually transitioned to 13-18 ‰ before or after overwintering, promoting its development and maturity (such as Jiangsu).

two。 It is best to use local materials to transport parent fish, cultivate them locally and avoid long-distance transportation as far as possible. The means of transport are cars, live water boats and so on. Parent fish can be packed in wooden stabs, canvas buckets, plastic fish baskets or oxygenated nylon bags. You can also put the fish in a nylon bag with holes, 1 in each bag, and then put the fish and the bag in the water of the human container to avoid collision. The transport of parent fish should be carried out when the water temperature is about 10 ℃, and should be shipped sparsely. In transportation, efforts should be made to keep the water quality fresh and oxygen sufficient. Nylon bag oxygenation anaesthesia can be used where possible. The commonly used anesthetic drugs are quinadine, barbitona, ether and MS-222. Chloral hydrate, tert-butanol, chlorobutanol, polyacetaldehyde, tert-amyl alcohol, etc.

3. For parent fish, the barracuda is generally more than 2 years old in males, weighing 0.5-0.75kg, while females are more than 3 years old and weighing more than 1-2kg, which can be used in the following year. Grey mullet generally uses 4-6-year-old 2kg female and 4-year-old 1.2kg male as parent fish. The parent fish caught from the sea in Taiwan is about 4 years old, with a body length of 32-50Cm and a weight of 1.0-2.okg. The parent fish raised in freshwater ponds should be more than 3 years old.

Generally speaking, it is better to choose the larger individual, not only the number of eggs is high, but also the offspring grow fast. However, attention should be paid to the ratio of male to female, because it is difficult to distinguish between male and female in appearance, so it is necessary to properly select more individuals with a body weight of 0.5-1kg to prevent unilateral selection of large individuals, resulting in a shortage of males during spawning. The selected parent fish are required to be physically strong, injury-free and disease-free.

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