True seedling breeding techniques

1. Cultivation pond and stocking density

Use a square or park-shaped cement pool with a volume of 25m3 to 100m3. Set the upper water, inflate and warm pipe valves in the pool. The drain outlet is located in the pool and passes through the pool outside drain. Before use, the cultivation pond is disinfected with potassium permanganate or sodium hypochlorite and exposed to sunlight. The stocking density was based on 10,000 fish/m3 to 20,000/m3 of newly hatched larvae oil.

2. Cultivation of water and conventional water quality indicators

Sand-filtered seawater is used during larval rearing. During early cultivation, UV disinfection of seawater can be used under conditions. During the cultivation period, the water quality in the pool was measured twice a day. The conventional water quality indicators were controlled as follows: water temperature 18-20°C, dissolved oxygen (D, 0) 4mg/l or more, total ammonia nitrogen (NH4-N) 1.0mg/l or less.

3, shading

During the cultivation period, an adjustable or shaded screen is placed above the cultivation tank to control the light intensity within 2000 lx. During the nursery period, chlorella was added to the cultivation water from the date of feeding the rotifers to keep the rotifers in the pond vigor, prevent starvation and nutrient decline, and maintain a good feeding environment. Chlorella in the pool is maintained at 500,000 cells/ml to 1 million cells/ml.

4, bait series and nutritional enhancement

The bait series of true oyster larvae can be simplified as: rotifers, Artemia nauplii (cephalopods, etc.), fish and shrimp.

(1) Rotifer

When the larvae were open (3 days after hatching), the rotifers were fed and fed in feeding water of 3/ml to 5/ml. When the larvae have a length of 7 mm to 8 mm, the food intake is large, and the feed density in the cultivation pond is difficult to maintain and the number of feedings can be increased. The rotifer feeds larvae to about 12mm in length.

(2) Artemia nauplii feeding

When larvae were about 6.5mm in length, Artemia nauplii was fed twice a day. The feeding amount was fed in 0.5 to 1/ml of feeding water, and then the amount of feeding was gradually increased with the growth of the fry. When larvae ingest large amounts of Artemia, feeding of cephalopods, fish eggs, newly hatched larvae and compound feeds should be increased.

(3) Feeding of fish and shrimp meat

When the larvae are 8mm to 9mm in length, they are fed with squid meat, the granules should be small, and the larvae should be fed in small amounts several times. The feeding amount of fish larvae should be gradually increased according to the feeding conditions of the fish. When feeding fish, shrimp, and meat, attention should be paid to changes in water quality to prevent oxygen deficiency. In addition, a variety of vitamins need to be added when feeding meat. In the conversion of bait, according to the degree of adaptation of the fry to the new bait, the feeding time and feeding amount of various bait should be adjusted to prevent individual differences from being aggravated and sudden death caused by broken bait.

(4) Nutritional enhancement of biological feed

The nutritive value of bait is high during the growth and development of juvenile oysters, while the highly unsaturated fatty acids (HUFA) contained in larvae and Artemia larvae are low, especially the contents of EPA and DHA are insufficient. , Often cause the survival rate of nursery is low, the deformity rate is high. Therefore, the strengthening of food fortification is one of the important measures in seed life.

The rotifer nutritional enhancement method: rotifers were introduced into 20 million cells/ml of chlorella at a density of 300 million/m3 to 1 billion/m3, and emulsified squid liver oil was added and cultured for 12 hours before use. Artemia nauplii were placed in fresh seawater with emulsified fish oil and cultured for more than 12 hours. It is better if fat-soluble vitamins and lecithin are added when nutrition is strengthened.

(5) Management of aeration and opening period

The truth is that there are squid fish, and the requirements for the amount of aeration during the opening period are usually different. During the nursery period, the arrangement of air stones was 1/1.5 to 2.0 m2. During the reclamation period, a slight flush (50 ml/min) was used. The aeration volume prevented the larvae from floating or swallowing bubbles or debris and caused false openings. Bubble disease. The length of the larvae during the reclamation period is 3.5-5.5mm. The larvae must have sufficient vitality to complete the reclamation. This requires that the initial bait has a high nutritional value, otherwise a low rate of reclamation will cause a large number of deaths or the formation of malformed fish. After larvae have been opened, they should gradually increase the amount of inflation. Some measures to improve the larval opening rate: First, the appropriate amount of aeration (50ml/min); Second, to keep the water clean; Third, feeding the initial high-nutrient food bait; Fourth, choose a strong vitality of the newly hatched larvae.

(6) Other management measures

1) Change water: The initial amount of water to be cultivated is 3/4 to 4/5 of the total volume. Gradually add water to the pool in the first 5 days. Change the water in microfluidic way at the age of 5 days. The water exchange rate is 20%. Then grow with the fry. Gradually increase the amount of water exchanged. When the water is changed at 10 days, the water exchange rate is 50%; at the age of 20 days, it is 100%; at the 25th day of age, the water exchange rate is increased to 200% when the fish and shrimp meal are started, and then the amount of meat consumed by the fish is increased. Increase, change the water rate to 500%.

2) Circulation culture: When larvae have a total length of about 6.5mm, they have a certain swimming ability. At this time, a circulation plate can be set in the cultivation pool to start circulation, and the circulation speed increases gradually with the growth of fry. The formation of circulation can promote the growth and development of fish fry and metabolism.

3) Clear bottom: The accumulation of feces, residual baits, dead fish, etc. at the bottom of the cultivation tank after about 12 days of age should be promptly cleared. The bottom is usually 2 to 3 days, and the latter is 1 to 2 days.

4) Isolation of weak seedlings: In the case of high-density cultivation, differences in individual size can easily occur for various reasons. When the total length is 10 to 15 mm, fry begins to enter the juvenile stage and changes in ecological feeding habits. Large individuals who grow well can easily attack small individuals that grow slowly, causing injuries to the body surface, fins, eyes, etc. resulting in bacterial infection. Onset, from the point of view of disease prevention, remove the attacked individuals at any time. At this time, large and medium-sized individual seedlings are mostly in the middle and lower layers of water, while small individual seedlings are active in the surface layer. This characteristic can be used to move small individual seedlings into other small containers for cultivation.

5) Counting: From the newly hatched larvae to 8mm in length (before 20-23 days of age), when the night larvae are evenly distributed, use a column sampler to sample evenly in the pool and calculate the total pool number. After a total length of 8mm, the swimming ability of the fry was enhanced and escape was rapid. The counting method described above was difficult to grasp and the error was excessive. At this point, the number of fry in the pond can be calculated by counting the dead fish by sucking the bottom. When out of the pool can be used small nets to fish fry gradually out of the container about 70L, accurate counting, and then standard samples and other samples measured until the total number of the pool.

6) Out of the pool: Under the condition of water temperature of 18-20°C, the full-length can be cultivated for about 50 days and the total length can reach 25mm~30mm. At this time, it is the best discharge specification. At this point, they should go out in time and go to the middle to cultivate. The pooling method is to reduce the water level of the cultivation pool to 50 cm, and surround the fry with a small fence, and then fish out the fish fry gradually using a soft net and a beaker and count.

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