A brief analysis of the factory and outdoor cage relay culture technology of Turbot
Wang Yufei
Turbot belongs to the flounder family , Turbot family , genus Rhododendron , is a benthic cold-water fish. The fish has strict requirements for seawater indicators such as temperature, salinity and heavy metals, and its most suitable growing water temperature is 14 °C ~ 18 °C, and the suitable salinity is 25 ~ 30. Turbot has been cultivated in this area for nearly 20 years, and at present, the aquaculture area of Turbot in Huludao City has exceeded 2 million square meters of water bodies, and it adopts the open land-based factory culture method of "greenhouse + underground well brine". The shortage of land resources and saline water resources in underground wells has constrained the development of the industry. In order to seek more and more suitable models for turbot culture in the region, from 2018 to 2019, we conducted relay tests on indoor factory facilities and outdoor cage culture in our region. The trial was a success and achieved considerable economic, social and ecological benefits. The test results are summarized as follows: [Jishan Huayao self-media network debut]
1. Materials and methods
(1) Test time
March 2018 to May 2019.
(2) Test site and conditions
The test site is The Seven Star Farm in Xingcheng City. The farm is a comprehensive farm with both a factory turbot farming workshop and a marine pond suitable for cage culture. The test pond is 500 m long and 80 m wide, running in a north-south direction with an average water depth of 3 m. The pond has convenient transportation, no pollution around it, timely tide absorption, sufficient tide, and water quality that meets the national first-class aquaculture standards. During the test period, the water temperature was 11 °C to 20 °C, the pH value was 7.5 to 8.0, and the salinity was 25 to 28.
(3) The production and setting of cages
1. Production of cages
The cage size is 5.0 m long, 5.0 m wide and 2.5 m high, the frame is welded with a diameter of 20 mm galvanized tube, and the cage material is a two-way extension of polyethylene nodular mesh, mesh 2a = 1.0 cm ~ 3.0 cm.
2. Installation of the cage
The float uses four cylindrical foams with a diameter of 40 cm and a length of 60 cm, which are evenly fixed to the surrounding frame of the installed cage, so that the upper part of the cage is 50 cm above the water surface. The sinker is a cement square, the size of which can make the cage stable as standard, and it is tightened and fixed around the bottom of the box with nylon rope. The setting of the cage needs to be noted: First, in order to prevent the fish fingerlings from being damaged by rubbing the wall of the box after entering the box, the new cage should be launched about 15 days before the fish species enter the box, and the cage is soaked, not only to deodorize, but also to make the box attach some algae; second, the bottom of the cage should be kept more than 1.0m away from the bottom of the pool. Since turbot is a benthic fish, the light should not be too strong, and it is better to take 500lx ~ 1500lx, so the cage should also be covered with a shade net.
3. Cage settings
The setting of cages should be determined according to the size of the water surface of the aquaculture pond, the number of cages set up and other factors. The test cage is set according to the group, the distance between the boxes in the group is 4.0m, the spacing between the groups is more than 100m, and the direction of the cage arrangement is perpendicular to the direction of water flow.
(4) Selection of seedlings
The criteria for selection are high-quality seedlings with consistent specifications, strong physique, strong vitality, normal body shape, no deformity, and no injuries and parasites. Because it is relay culture and the breeding time is short, this test selects large-sized seedlings, with an average of 400 g/tail, a total of 10,000 fish.
(5) Transportation
Since the relay culture test was carried out in one farm, the two places are relatively close to each other, and no special transport vehicle is required. We use buckets with water for transportation, no damage, survival rate of 100%.
(6) Delivery
It will be released on April 15. In April, the temperature of outdoor ponds in the area is still low, and sometimes there are cold snaps. Since turbot seedlings are more sensitive to changes in water temperature, it is necessary to choose sunny weather when the turbot seedlings are stocked, and the temperature difference should not be too large when the seedlings are put into the box, so as not to exceed 2 ° C and the salinity is within 5. Care should be taken to avoid re-injury to the fish. The culture density is about 300 fish/crate for a total of 33 cages.
(7) Feeding of bait
At present, the bait mode of turbot culture in this region is to invest in full-price granular feed at the seedling stage, and feed the small trash fish until it is sold out of the pond when the fish can feed on small trash fish. In order to avoid the stress of the fish due to the change of bait and affect the growth of the fish, we still fed small trash fish during the trial period. Feeding method is: 4 times a day in the early stage, 2 times in the morning and afternoon, 3 times a day in the later stage, 1 time in the morning, middle and 1 time in the evening, and the specific amount and frequency of bait should also be adjusted in time according to the weather, water quality and fish feeding status.
(8) Daily management
1. Regular inspections
The content of the inspection is: First, the inspection of the fish. Patrol the activities and feeding conditions of fish, whether there are diseases or not; the second is the inspection of cages. Lift the cage around, check whether the cage is damaged, and repair it in time after discovery; the third is to inspect the pond. Check the pond's levees and gates for leaks and changes in the water level in the pond. Be careful not to check the box during feeding so as not to affect the feeding of the fish; in addition, adjust the depth of the cage in time according to the change of water level; in addition, after the fish species are put into the box, the inspection should be insisted on every day.
2. Clean the cage
Due to the large amount of debris on the surface of the pond, coupled with the fact that the water in the pond is almost non-flowing, the cage blockage during the test process is more serious, which affects the water exchange and the growth of turbot, and we clean and wash the cage in time according to the actual situation of the pond patrol.
3. Aquaculture records
The content of the record is: the number of fry, water temperature, water quality, baiting, disease prevention and control during breeding, regular monitoring of turbot and sales out of the box. Growth testing is required at least every 15 days in order to observe fish growth and adjustments to the feeding rate in a timely manner. The measurement results are shown in Table 1.
Table 1 Statistical table of weight, body length and water temperature measurement during the test period
(9) Disease prevention and control
The ancients said: "The saint does not cure the disease and cures the disease." In the process of the test of turbot cage culture, although the time is short, the principle of prevention and control is still adopted for fish diseases, and the specific methods are as follows: select healthy, disease-free fry; in the process of stocking and growth detection, adhere to the operation process of light handling, light release, careful, to avoid fish body injury, causing fish disease; because it is fed small trash fish, small trash fish should first be selected fresh, and each time to clean, disinfect and then feed In the breeding process, it is also necessary to sprinkle 15 ppm of quicklime and 0.3 ppm dibromohydantoin in the cage as appropriate. There were no diseases throughout the trial.
Second, the test results
Seedlings were stocked on 15 April 2018 and sold or returned to greenhouses on 25 May when the pond temperature was around 18°C. After 40 days of outdoor cage culture, the average weight of turbot increased from 400 g/tail to 660 g/tail, and the net weight gain was 260 g/tail, reaching the specifications of commercial fish. A total of 6270 kg of turbot commercial fish was obtained, with a survival rate of 95%, and it was sold on May 25. Stocking and harvesting are shown in Table 2.
Table 2 Stocking and harvesting
3. Discussion
Turbot is a benthic cold-water fish with a suitable growth temperature of 14 °C to 18 °C. From mid-April to the end of May, the outdoor sea temperature in this area is exactly 14 °C ~ 18 °C, which is suitable for outdoor culture of Turbot, and the experiment has proved that the culture mode is successful. However, in the choice of breeding sites, it should be noted that the aquaculture sea surface is not too small, the depth is not too shallow, the reason is that the temperature in our northern region is unstable in April, and sometimes there will be cold current cooling weather, the area is too small, the water level is too shallow, and the water temperature changes too much, which will affect the growth of turbot. There are currently 500,000 hectares of marine aquaculture in the region, although this test was carried out in ponds, if the sea conditions are suitable for turbot cage culture, this culture model can be extended to the sea area for turbot cage culture.
Ponds or sea areas, the area set on the cage is not as much as possible, the setting is less, the waste of water bodies, too much setting not only affects the breeding environment, but also is not conducive to the growth of fish. Experiments have shown that the pond set cage area is less than 20% of the pond water surface.
According to the growth law of turbot and consumers' consumption habits of turbot, the average weight of turbot selected in this experiment is 400g/tail, which can be increased to 660g/tail after 40d outdoor cage culture, with an average net weight gain of 260g/tail, reaching the specifications of commercial fish. In addition, large-sized fry in the breeding process of disease resistance is stronger, the survival rate is also higher, the test has proved that the indoor and outdoor relay culture of Turbot in this area to choose large-sized seedlings, it is best to average weight of more than 400g / tail.
Turbot factory facility culture is the dominant species and main promotion mode of marine aquaculture in Huludao City. Due to the disorderly development of turbot farming in the past, the amount of salt water mined in Huludao City has exceeded the natural supply, the well saline water resources in local areas have shown a gradual decline trend, and some breeding areas have begun to lack water, coupled with a round of environmental protection and marine supervision of the high pressure situation, the cultivation of turbot in this region and the enthusiasm of turbot farmers in this region have declined. Previously, the region has tried the "north fish south culture" model of turbot, which has also been successful. However, due to the fact that the main breeding area of "North Fish And South Culture" of Turbot is Fujian, which is more than 2,000 kilometers apart, and the seed is transported over a long distance, not only the cost of breeding increases, but also has a certain impact on the survival rate of the fry. The success of indoor factory facilities and outdoor cage relay culture in the area of Turbot, on the basis of the success of the "North Fish South Culture" model of Turbot Turbot, has added a new model for turbot farming in the region, which is of great significance to the health, stability and sustainable development of the industry.