CATDOLL : CATDOLL: Cultivation and breeding of turbot

Artificially cultured broodstock can produce mature eggs from January to October under artificially controlled light conditions. Artificial insemination is still used for artificial reproduction. In 1972, the UK successfully cultivated turbot seedlings, but it has only reached the level of small-scale production so far, indicating that artificial cultivation of turbot is somewhat difficult. In the UK, the survival rate from hatching to metamorphosis is only 1%-25%. The average is only 3%-6%. Fertilized eggs are incubated in still water or running water, and the incubation water temperature is 12℃-15℃. The newly hatched fry are cultivated in a circular fiberglass tank or cement pool with a volume of 10-20 cubic meters, with a cultivation density of 5-20 fry/liter, continuous light for about 14 hours a day, and the water surface illumination is 200-1000lux. During the cultivation period, the water temperature is slightly aerated and gradually increased to 20℃. Feeding begins on the third day after the fry are hatched, and rotifers are fed twice a day, with a rotifer density of 5-10/ml. In the first ten days, add some monocytic algae (preferably triangular brown finger algae and isochrysis) as bait for rotifers. Feed Artemia nauplii 6-10 days after hatching, and feed Artemia nauplii for a total of 20-25 days. When the fry reaches 20 mm in length, feed artificial compound feed. This will encourage the fish to change their food and gradually weaken their preference for live bait. The survival rate of turbot after changing its diet reaches 85%. It takes about 70 days for the fry's eyes to move to one side to achieve complete metamorphosis, and the total length is about 30 mm. Generally, the survival rate of turbot artificial breeding is calculated at this time. The fry that have completed metamorphosis at 80 days can be moved to a larger pond of 20-30O and fed with all workers' compound feed. The lighting, water flow and aeration measures at this time are the same as before.

Turbot grows quickly. It only takes 10 to 12 months from spawning to growing commercial fish for sale (0.8 to 1 jin). If you invest in the same year, you will get profit in the same year. Moreover, it has high economic value, high feed conversion rate, strong disease resistance, low oxygen consumption, and is suitable for high-density breeding. It is a promising and excellent breeding variety. Females grow faster than males, and the body length of females is significantly longer than that of males. When they reach sexual maturity at the age of 2, the length of males can reach 20 to 25.5 cm, and that of females can reach 30 to 35.6 cm.

Facility conditions

The breeding farm should be located far away from pollution sources, with convenient communication and transportation, sufficient electricity and fresh water. The water quality is clear and meets the national fishery secondary water quality standards (you can consult the local fishery administrative department). The broodstock breeding facilities include temperature control, light control, aeration, water inlet and outlet, and water treatment facilities and equipment. The broodstock breeding pool can be made of wooden troughs (lined with rubber inner wall), fiberglass tanks and cement pools. The pool shapes are square, rectangular, round and octagonal. The volume ranges from 10 to 100 cubic meters, the general volume is 20 to 60 cubic meters, and the pool depth is 0.6 to 1.2 meters. The water inlet is set at the top of the pool according to the tangent or diagonal direction, and the central drainage outlet of the side reed is set in the center of the pool. After the pool water circulates, it is discharged out of the pool through the central drainage column. The drainage column outside the pool is composed of inner and outer casings, which can match the central drainage column to freely adjust the water level and flow rate in the pool.

Seedling cultivation facilities should include seedling cultivation rooms, biological feed cultivation rooms, aeration facilities, temperature control facilities, water treatment facilities (including ultraviolet disinfection equipment) and water inlet and outlet facilities, etc. Seedling cultivation pools are divided into early cultivation pools, late cultivation pools, and intermediate cultivation pools.

Preliminary cultivation pool: a circular or square cement pool with an area of ​​10-200 m and a depth of 0.8-1.0 m.

Late culture pond: area 20~40O, water depth 1~1.5m, with independent inlet and outlet; the bottom of the pond is inclined towards the drainage hole at a certain slope to facilitate drainage.

Intermediate cultivation pool: a circular or square cement pool with an area of ​​30 to 500 square meters and a depth of 0.8 to 1.0 m, which requires good water circulation and sewage discharge functions.

Broodstock selection

There are two sources of turbot broodstock: one is to select from wild populations; the other is to select from farmed populations. China is not the origin of turbot, so it mainly relies on the second way to obtain broodstock. Under normal breeding conditions, only about 50% of turbot broodstock females ovulate during the production season, and other females either do not spawn or spawn late, and the quality of eggs varies greatly, so the seedling breeding farm should maintain a sufficient number of broodstock, usually >100. Turbot is dioecious and lacks secondary sexual characteristics. The difference between male and female broodstock is mainly gradually revealed through the periodic development process. Female individuals are larger, the fatness of the body increases before spawning, and the gonads are prominent; male individuals are relatively small, the fatness of the body is average during maturity, and the gonads are not prominent. Broodstock should be complete in body shape, normal in color, healthy and uninjured, active, clustered, active in feeding, and of appropriate age and size. Female fish must be over 3 years old, weigh over 3 kg, and be over 40 cm long; male fish must be over 2 years old, weigh over 2 kg, and be 30-35 cm long. The ratio of male to female broodstock entering the pond is 1U1 or 1U1.5. Broodstock can be used up to 6 years old. Broodstock are transported in low-temperature insulated foam boxes at a temperature of about 10°C, 1-2 fish/box. Broodstock transported in the current breeding season should generally be for the next breeding season.

Artificial insemination

Turbot is a fish that lays eggs in batches and can lay eggs multiple times in each spawning season. After the eggs of turbot mature, they first enter the reproductive cavity, and then artificial insemination can be used to squeeze the eggs for fertilization. Each female turbot has a regular ovulation interval, but the individual ovulation cycle is different: the shortest is 60 (±4) hours, the longest is 113 (±2) hours, and most are between 80 and 90 hours. At 12 to 14°C, eggs must be squeezed within 10 hours after ovulation to ensure the maximum survival of the eggs. This time limit is affected by the water temperature. When artificial insemination, first dry the fish body and the container to prevent water and excrement from mixing in. Then add 1-5 ml of semen to 1×105 eggs, stir quickly to make the sperm and eggs fully contact, and then add a small amount of seawater filtered by sedimentation sand, so that the volume ratio of semen, eggs and water is about 0.5U100U100, continue stirring for 1 minute, then let it stand for 5 minutes, add seawater, let it stand for 10-15 minutes, after it absorbs water and expands, rinse it with clean water 1-2 times, put it in a 2000ml measuring cylinder, and add seawater to separate the floating eggs and the precipitated eggs. Record the number of floating eggs, and put the floating eggs into the incubator for incubation after disinfection. The egg diameter of turbot eggs is an important indicator of egg vitality. When the egg diameter is 0.9-1.1mm, the fertilization rate is high, while the egg diameter is 1.1-1.2mm, the fertilization rate is medium or low, and the fertilization rate of eggs below 0.9mm is the worst. High-quality fertilized eggs are transparent, round, and have a small perivitelline space. The 1st and 2nd divisions after fertilization are clear and symmetrical. If you need to transport fertilized turbot eggs, the packing density depends on the distance of transportation, generally 3,000 to 150,000 eggs/L. The oxygen-filled bag must be kept at a low temperature during transportation.

Hatching fry

The fertilized eggs of turbot are buoyant in seawater, so the conventional floating egg hatching method is adopted. The commonly used hatching containers are small glass tanks (25-130L) and large fiberglass tanks (1-10m3) or cement pools (10-20m3). One or more hatching cages can be placed in the hatching tank (or pool). The hatching cages are generally about 80cm×60cm×60cm, so that they are floating, and the upper mouth of the hatching cage is about 10cm above the water surface. In order to keep sufficient oxygen in the hatching pool, the water in the hatching pool should be kept circulating, and several inflatable stones can be used to inflate the water to keep the dissolved oxygen level in the hatching pool above 6mg/L. At the same time, an air stone is placed in the center of each hatching box to maintain water flow so that the fertilized eggs are evenly distributed in the water. The daily water circulation volume of the hatching pool should be maintained at 2-3 scales, and the number of sunken eggs should be counted every day and sucked out in time. The following conditions should be met during hatching: water quality should meet the national fishery water quality secondary standard (you can consult the local fishery administrative department); direct sunlight should be avoided, the illumination is 100-1000Lux, 500Lux is preferred; water temperature is 10-16℃, 12-15℃ is preferred, salinity: 28-35; pH7.8-8.2; dissolved oxygen>6mg/L; ammonia nitrogen<0.1mg/L. Fertilized eggs are placed in a 0.5-1m3 hatching cage at a density of 300,000-600,000/m3. Under 12-14℃ conditions, fertilized eggs can hatch within a week. There are two ways to lay out the pond: one is to collect, rinse, and count the eyed eggs and lay out the pond directly; the other is to carefully move the newly hatched fry after the membrane is broken into the feeding tank with a smooth container, adjust the water and gas volume to ensure sufficient dissolved oxygen, remove dead fry, maintain cleanliness, and enter the seedling cultivation program.

Seedling cultivation

If you are buying seedlings, you should choose seedlings that are more than 5 cm long. Before purchasing seedlings, you should inspect the parent fish germplasm, seedling quality and technical level of the nursery. You must buy from a national-level breeding farm or a government-designated nursery. The seedlings must be complete in shape, without injuries, deformities, or albinism. The specifications of the same batch of seedlings are neat, with both eyes located on the left side of the body. The side with eyes is bluish-brown with dotted melanin, and the side without eyes is smooth and white. The surface of the fry is bright and smooth, without scars, darkening or redness, strong mobility, neat gill filaments, and no inflammation or parasites.

Seedling transportation: Before transporting the seedlings, stop feeding and cool down the fish in advance. Generally, nylon bags are used for oxygenated transportation, and the transportation time is preferably within 20 hours. First, add about 1/3 of sand-filtered seawater into the bag, count the fry, put them into the bag, oxygenate them, seal them, and then put them into foam boxes or cartons for transportation. A 10-liter bag can hold 50 to 100 fry with a total length of 5 to 10 cm; each bag can hold 30 to 50 fry with a total length of 15 cm. During the transportation of fry, try to avoid fish injuries, collisions, bag breaks, air leaks, water leaks, and lack of oxygen. When the water temperature is high or the transportation distance is long, a small amount of ice should be added to the transport bag to cool down and inhibit bacterial growth.

Pond entry conditions: The temperature difference of the fry in the pond should be controlled within 1-2°C, and the salinity difference should be within 5. This can reduce the stress response of the fry due to environmental changes.

The biological baits used in turbot fry cultivation mainly include marine chlorella, rotifers and Artemia. Marine chlorella is Pseudochromonas. In production, the one-time cultivation method is mostly used. The batch and scale of cultivation are mainly determined according to the turbot fry production process and the needs of fry and juveniles, the time and quantity of feeding. The rotifer is Brachionus plicatilis. Rotifer cultivation generally adopts one-time cultivation method and continuous cultivation method, or a combination of the two methods. The cultivated rotifer must be nutritionally fortified, and the purpose of nutritional fortification is mainly to increase the content of unsaturated fatty acids. There are two ways to strengthen. One is to feed rotifers with marine microalgae rich in EPA/DHA, such as triangular finger algae, Isochrysis, chlorella, and microchloropsis. Among them, chlorella and microchloropsis are the most common; the second is to use artificial fortifiers rich in EPA/DHA, such as squid oil, fish oil and other products. Strengthening cultivation is carried out 6 to 12 hours before feeding the fry. Artemia is incubated in an Artemia incubator, and the larvae are separated and nutritionally fortified before being harvested and fed to turbot fry. The fortification of Artemia is similar to the fortification method of rotifers.

Intermediate cultivation

60-70 days after hatching, the seedlings can reach 3cm. At this time, most of the seedlings have completed metamorphosis and gradually turned to bottom-dwelling life. In order to improve the quality of cultured seedlings, it is necessary to enter the intermediate cultivation stage. Only when they are more than 5cm can they be used as commercial seedlings for aquaculture. Before stocking, soak and disinfect the seedling pond with bleach, rinse it clean, and add filtered seawater for standby use. For seedlings with a total length of 3-5cm, the stocking density is 1000-2000 tails/O. During the cultivation period, the feed requires balanced nutrition. High-quality compound feed can be used, or homemade soft granular feed can be used. In the early stage of feeding, feed 8-10 times a day, and gradually reduce to 3-4 times as the fish grows. In order to prevent contamination by residual bait, the pond water must be drained after each feeding, and the precipitated residual bait and feces must be removed, and the oil film must be removed. The water change volume is 8-10 cycles per day. Under normal circumstances, the survival rate of seedlings from the initial hatching of fry to the commercial seedling stage is 10-20%, and the highest can reach about 30%.

Leaving the pond: Turbot fry are usually collected and removed from the pond by drainage. During the operation, damage to the fry should be avoided. The quality and specifications of the fry should be tested before leaving the pond.

Transportation: The transportation methods for seedlings include box-type or barrel-type container air-filled transportation, live water boat transportation, which can be selected according to the specific situation. The temperature and salinity of the water used for transportation can be adjusted in advance according to the requirements of the culture water environment. Seedlings should be stopped from feeding for more than 1 day during transportation.

Fingerling stocking

Control and adjust the stocking density. In actual production, the stocking density should be adjusted as necessary according to the exchange volume of pond water and the growth of fry. The following factors should be considered when controlling the stocking density:

When the pool water exchange volume is less than 6 scales per day, the density should be appropriately reduced; when the exchange volume is more than 10 scales per day, the density can be increased as appropriate; the density can also be increased or decreased based on the amount of dissolved oxygen in the monitored water.

Fish are sampled and weighed every month to decide whether to adjust the density.

Make full use of the breeding area. Neither reduce the growth rate of fish in some breeding ponds due to over-stocking, nor waste the breeding area due to too low stocking density.

In order to prevent excessive pond division operations from causing stress reactions and affecting the growth of fish, adequate planning must be done before each pond division and pond emptying to ensure that the stocked fish remain stable in one pond for at least a period of time before pond division operations are carried out.

Feeding

The basic requirement of turbot for feed is high protein and medium fat. Compared with other carnivorous fish, its demand for fat is slightly lower. If high-fat feed is fed for a long time, the liver function will be reduced. In order to make turbot grow healthily, it is necessary to feed it with feed suitable for each growth stage of turbot. The protein content in the feed during the seedling stage (including the juvenile stage) is required to be 45-56%; during the grow-out stage, the protein content in the feed is 45-50%. The demand for fat of turbot is relatively low. The fat content in the feed during the seedling stage is about 10%, and in the grow-out stage it is 10-13%. The most suitable C/P ratio (energy to protein ratio) is about 65% during the seedling stage; as the fish grows, the C/P ratio of the grow-out feed increases to 65-76%; the C/P ratio of the feed used before leaving the pond reaches 80%.

The feed used for turbot farming should be suitable for the nutritional needs of different growth stages, including appropriate amounts of multiple vitamins, minerals and highly unsaturated fatty acids. The feed used should be easy to feed, the feed pellets should be well formed and not easy to disintegrate in water. When purchasing feed, you should check whether the feed label indicates the following: it should be marked with the words "This product meets the feed hygiene standards" to indicate that the product meets the provisions of GB13078; indicate the guaranteed value of the main ingredients, that is, the content of crude protein, crude fiber, crude ash, calcium, total phosphorus, salt, moisture, amino acids, etc.; indicate the standard number, production license and product approval number implemented in the production of the product; specifications, models, net weight, production date, shelf life, name and address of the producer, etc. In order to prevent pathogens from being brought into the fish pond from the feed, it is recommended that factory farming prohibit the use of wet pellet feed and any fresh feed.

Since turbot is a cold-blooded animal, the amount of food it eats varies greatly under different water temperatures. Generally, the daily feeding rate is 6-4% during the seedling stage, about 2% when it grows to 100 grams, and about 1-0.5% when it grows to more than 300 grams.