CATDOLL : CATDOLL: Artificial breeding of large yellow croaker

There are currently a variety of farming models for adult yellow croaker, including cages, enclosures and earthen ponds, all of which have achieved significant results and good economic benefits. Here we introduce the cage farming of adult yellow croaker.

The requirements for the cage setting in the grow-out stage of large yellow croaker are basically the same as those in the fish breeding stage, except that the cage specifications and mesh size change as the fish grow. The depth of the grow-out cage is generally between 3.5 meters and 4.0 meters, and the mesh size is between 20 mm and 60 mm. To avoid scratches on the fish body, it is better to choose a softer nodular mesh as the net material.

Fingerling stocking

1. Selection of fish species

The fish species to be stocked should be well-proportioned, strong, with intact scales, and free of disease and injury. The size of the fish species stocked in the same cage should be uniform. For cages that are planned to reach a size of more than 400 grams in the same year, the size of the fish species stocked should be around 100 grams.

2. Transport of fish species

There are many ways to transport fish species, including live water boats, live water trucks, fish baskets, water tanks, plastic bags filled with oxygen, etc. For productive long-distance transportation, live water boats are preferred. It is generally better to transport fish species in late autumn when the water temperature drops to 18℃~16℃, or in spring when the water temperature rises to above 13℃. Fish species during the disease period or after being full should not be shipped. Live water boat transportation should be carried out in warm and windy weather. The reference density for live water boat transportation for more than 24 hours is 500 fish/cubic meter (specification 75 grams), which is about 40 kilograms/cubic meter. The density of transportation in other water bodies is much smaller than that of live water boat transportation.

3. Stocking of fish

For cages in fast-flowing sea areas, stocking of fish should be done during low tide. After the fish are transported to the cage area, they can be disinfected by soaking them in a freshwater solution with a high concentration of antibiotics and an appropriate amount of formalin, taking into account the time interval between catching the fish and putting them into the cage. When using closed water bodies to transport fish, sudden changes in water temperature and other conditions should be avoided when entering the cage. A short transitional treatment can be carried out by adding seawater from the cage area to the transport water body. The stocking density of fish is determined by the water flow in the cage and the specifications of the fish. The reference density is about 25 fish/m3 for 75 grams, and the density before harvest is 12 fish/m3 to 14 fish/m3, that is, 6 kg/m3 to 7 kg/m3.

Feeding

1. Feed types and processing

The feed for large yellow croaker in the growing stage is generally based on frozen mackerel and mullet, supplemented with powdered compound feed, and then fed after processing. Processing method: First, use a knife or meat slicer to cut the mackerel and mullet into palatable fish pieces. This method is convenient to process and is not easy to collapse in water. The disadvantage is that it is not convenient to add additives and the nutrition is relatively simple; second, the frozen fish is minced into minced meat, and mixed into a sticky ball feed, squeezed into blocks of different sizes by hand, and put into the net cage. This method can be mixed with some powdered compound feed, or other fish, shellfish and other feeds, and it is also convenient to add vitamins, etc., and the nutrition is comprehensive. Large yellow croaker is a carnivorous fish with a high demand for protein. According to preliminary tests, the protein content of artificial compound feed in the growing stage should be around 45%, and the carbohydrate content should be controlled at around 5%.

Frozen mackerel is easily oxidized during the thawing process, the color becomes darker, the meat becomes soft, and the quality is significantly reduced. Therefore, before processing, it is advisable to use mechanical methods to break up the frozen fish, and then soak it in seawater for a while, so that the surface of the feed fish can be thawed, and the water can be drained before processing. The fish paste processed in this way is lighter in color and has better freshness. Mackerel should not be thawed by soaking for a long time or by sunlight.

During the high temperature period, it is also good to feed fish with powdered compound feed or floating extruded feed. The effect is better if powdered compound feed and floating extruded feed are used alternately. When using floating extruded feed, the feed should be soaked in 1:1.5 fresh water for 20 to 30 minutes to allow the feed to completely absorb water before feeding.

Complete artificial feed

Due to the large amount of frozen fish in the head and tail of the breeding process, a large amount of bait pollution has been caused, which has brought about the frequent disease problems of yellow croaker. In 2012, drawing on the research results of largemouth bass, Shanghai Ocean University and Shanghai Nonghao Feed Co., Ltd. trial-produced a complete feed for yellow croaker, and conducted a productive breeding test in Ningde. The results showed that the compound feed can completely replace the frozen fish; at the same time, the products raised with compound feed have obvious advantages in color and flavor compared with the products raised with frozen fish, and can be comparable to the products of local large cage breeding (semi-wild). Raising yellow croaker with compound feed can solve the problem of frequent diseases of yellow croaker caused by bait pollution to a certain extent, and will play a huge role in promoting the development of the yellow croaker industry.

2. Feeding technology

During the growing period, large yellow croaker is generally fed once in the morning and evening; during the wintering period (water temperature 10℃～15℃), it is generally fed once a day; in rainy weather, it can be fed once every other day.

The daily feeding rate is mainly determined by the feeding situation of the previous day, as well as the weather, water color, tidal changes, whether the farmed fish have been moved, etc. The daily feeding rate of wet feed is about 5% of the weight of the fish in the pond during the high temperature season (water temperature above 29°C), as high as 6% to 8%, and less than 1% during the winter.

During the growing stage of large yellow croaker, the feed coefficient of processed chilled feed is slightly higher than 5.

Before and during feeding, try to avoid people walking back and forth, otherwise it will affect the feeding of yellow croaker.

Management Operations

The management and operation of the large yellow croaker cage culture stage is basically the same as that of the fish seed breeding stage. However, it should be emphasized that the fastest growth in the culture stage is during the high temperature period, which is also the season when epiphytes are most likely to attach to the cages. The cages should be changed and cleaned frequently, generally once every 30 days or so. In conjunction with the change and cleaning of the cages, the farmed fish in the cages should be sorted out to remove large and small sizes, leaving medium-sized ones, and be immersed and disinfected with antibiotics, fresh water solutions, etc.

In order to maintain the natural golden color of commercial large yellow croaker, it is best to cover the cages with shade curtains in the later stages of culture. In contiguous cage farming areas with poor water flow and fertile water, it is necessary to check the dynamics of the fish three times a day, morning, noon and evening, especially in hot and humid weather, and pay special attention to early morning inspections to prevent fish from dying due to lack of oxygen.

Disease prevention and control

1. Disease symptoms

Some fish have white spots on their body surface, which expand into white patches. Some fish have entire tail fins ulcerated and their eyes turn white, similar to symptoms of cataracts. In severe cases, the eyeballs become red, swollen, congested, protruding or falling off, the body muscles ulcerate, the head is worn and exposed in a honeycomb shape, and is congested and inflamed. Sick fish become restless and swim wildly, or rub against the nets to cause scales to fall off, causing secondary infection and loss of appetite. Some remain stagnant on the water surface, become weak, swim slowly, and die one after another.

2. Pathogen diagnosis and characteristics

The scales, stripes and mucus from the white spots of the diseased fish were scraped off and observed with a dissecting microscope (5×10), and a constantly wriggling worm body was found. It was oval in shape, flat dorsally and ventrally, with a sucker on each side of the front end and a holdfast at the back end, with 3 pairs of large central hooks and 8 pairs of small edge hooks. The mouth was behind the front sucker and it was constantly swallowing. It was connected to the pharynx and 2 branch-like intestines below, with 2 pairs of eye spots on both sides in front of the mouth. The worm body was translucent in appearance, and its morphological characteristics were very similar to those of Benedenia. At the same time, the diseased fish was placed in a bucket and immersed in fresh water for observation. After immersion for 2 to 3 minutes, a large number of worms were found to fall off the surface of the diseased fish and turn white, so it was confirmed to be caused by Benedenia.

Benedenia belongs to the subclass Polyhedralis, order Loculata, family Loculidae. The body of the worm is oval, flat dorsally and ventrally, generally 5.4 mm to 6.6 mm in length, the longest can reach 11.6 mm, and the width is generally 3.1 mm to 3.9 mm. The front of the body is slightly protruding, with an anterior sucker on each side of the front. There is an oval posterior sucker at the rear end of the body, which is much larger than the anterior sucker. There are 8 pairs of small notches on its edge and the edge of the marginal membrane on its inner surface, 7 pairs of marginal hooks, 2 pairs of anchor hooks and 1 pair of appendages in the center. The mouth is at the rear edge of the anterior sucker, and below the mouth is the pharynx. There are 2 pairs of black eye spots from the pharynx to the back. The reproductive system has 2 testes, generally located in the center of the body, with a prostate storage sac and a copulatory organ under the pharynx; 1 ovary, yolk glands are scattered throughout the body, and there is a yolk storage sac in front of the yolk.

III. Prevention and Control Measures

1. Add 20ppm of furazolidone to fresh water and soak the infected fish for 5 to 10 minutes. Inflate the water during the soaking process and observe the fish's tolerance. If the fish is found to have abnormal conditions such as falling over, it should be immediately removed and put into the net cage for recovery. This method can effectively kill Benedenia, but it is difficult to kill the eggs. In order to consolidate the therapeutic effect, another drug bath is required 5 to 7 days after medication to prevent Benedenia in large water bodies from parasitizing again. This method is used to prevent Benedenia disease in large yellow croaker. It is safe and reliable, but the operation is troublesome and the fish body is easily damaged.

2. Use woven cloth to make a net cage cover. When treating fish diseases, put it on the outside of the fish cage for disinfection and treatment. Add 300ppm~400ppm formalin + 20ppm furazolidone and soak the sick fish for 20 minutes to 30 minutes. Or when the tide is flat, do not use woven bags, just lift the net cage, the water depth is 0.5m~1m, and use the above-mentioned two drugs to spray, maintain the concentration of the drug bath for 20 minutes to 30 minutes, and pay attention to observe whether the fish has any abnormal phenomenon during the soaking process. The advantage of this method is that there is no need to move the fish body, and the stress reaction is small.

3. Use "Long-acting Bacteria and Toxins Clearing Powder" (trichloroisocyanuric acid) to dilute and dissolve with seawater and then evenly sprinkle. The medication should be used in the early morning or evening when the fish are floating. It is best to choose to apply the medication during low tide, because the water flow is slow during low tide, the efficacy is maintained for a long time, and the loss is slow. Use 1.0g to 1.5g of medication for each net cage (2.6m x 3.6m), sprinkle once in the morning and evening. For those with mild disease, only sprinkle once a day, and use the medication continuously for 5 to 7 days. There is no need to lift the net cage when using the medication. This method is the simplest and has a better therapeutic effect, but this drug is a strong chlorine agent, the dosage must be properly controlled, and attention should be paid to evenness when splashing.

IV. Preventive measures

1. Change the nets in time. During the high temperature period, change the nets every 5 to 10 days to remove the eggs of Benedenia adhering to the nets in time, thereby reducing the density of larvae in the water.

2. Before the epidemic season of Benedenia fish disease (June to October), drugs can be used to form a disinfection area at the four corners of the cages. Five to six "Long-acting Bacteria and Toxins Clearing" tablets (trichloroisocyanuric acid) can be hung on each cage. The depth of the hanging bags is 50 cm to 60 cm. This can remove Benedenia and other pathogenic bacteria and pathogens in the water, thereby purifying the water and achieving the purpose of prevention.

Treatment options for visceral white spot disease

Symptoms: In the early stage of the disease, the fish have no obvious symptoms on the body surface, only slow reaction, decreased appetite, and then float to the surface of the water without the group, swimming alone or resting at the bottom of the cage. The weaker ones will die soon, and there are almost no symptoms on the body surface, but as the disease worsens, some fish will have white or light yellow spots on the body surface. The body surface is damaged and ulcerated, bleeding and red, and the tail fin and chin are also bleeding and red. Then the death rate gradually increases. Dissection observation shows that the internal organs of the sick fish have obvious lesions accompanied by ascites, and the liver, spleen, kidney and other internal organs are slightly enlarged, and are covered with a large number of irregular and spherical white or light yellow nodules, the spleen is the most obvious. These white spots are formed by a layer of fibrous tissue wrapped around the colony. When there are many white spots in the kidney, it is anemic, and when there are many white spots in the spleen, it is swollen and dark red. The contents of the white nodules are smeared and examined under a microscope, and a large number of short or slender bacteria are found, which are fish-killing Pasteurella and Nocardia. As for the treatment plans for the above symptoms, after using the medicine on large quantities of fish on the Xiabaishi Bendoukeng and Qingshan fishing rafts, it has been proven that the following three plans have unique therapeutic effects.

Plan 1: Mix per kilogram of fresh feed: 4g of fluphenazine + 4g of doxycycline + 5g of liver-stimulating agent + 6g of multivitamin B for aquaculture, use for 3 consecutive meals, generally for fish weighing more than 150g.

Plan 2: Mix every kilogram of fresh feed with: 8g of Jinpinjiajundi No. 1 + 3g of ampicillin + 5g of Gansuning + 5g of VC for aquatic products, and use it for 2-3 meals. This plan is suitable for fish of various sizes.

Solution 3: Mix 5g of Jinpin Chuanlijia + 5g of Gansuning + 6g of VC for aquatic products per kilogram of fresh feed, and use it for 2-3 meals. This solution is very effective for fish under 150g. Generally, the mortality rate will drop by 1/3 to 1/2 after one meal of medication.