Shallow sea and tidal flat are the first choice for the development of marine aquaculture, and the development of marine cage fish culture is an important means for the development and utilization of shallow sea and marine fish culture, which is of special significance in the development of fishery in China today.
1. What's the significance of developing fish culture in seawater cages?
China is a big country with a population of nearly 654.38+300 million, and food security has become the top priority of China's development. Aquatic products are the main source of human protein. Developing fishery production is of special significance for alleviating the pressure of population growth on food production in China, increasing the supply of high-quality food in protein, improving the health quality of the people, effectively developing and utilizing land resources, and ensuring farmers and fishermen to increase production and income under the current situation. Developing cage fish culture in seawater is an effective way to effectively develop and utilize shallow sea land resources and an important means to develop fishery production, especially today when China's marine fishing industry implements the "zero growth" strategy. This is because:
(1) can effectively expand the space of mariculture.
Shallow seas, ports and beaches are good habitats and breeding grounds for most marine life. Because this area has good lighting conditions, suitable water temperature, rich bait biological resources and suitable hydrological conditions. Therefore, this area is also an excellent place to develop mariculture. In the past 20 years, the development of marine aquaculture in China has been concentrated in this water area, forming a situation in which fish, shrimp, shellfish and algae develop together and shallow seas and beaches are used together. By 2000, China's mariculture area had reached 654.38+08.656 million mu, accounting for 654.38+09. 1% of the total aquaculture area in China, including shallow sea aquaculture area. The tidal flat culture area is 6.5438+0.0294 million mu, and the total aquaculture output is 6.5438+0.0061.2 tons, including 427,000 tons of fish, 343,000 tons of crustaceans, 8.607 million tons of shellfish, 6.5438+0.202 million tons of algae and 34,000 tons of others, accounting for 244,000 tons of the total aquatic products in China.
In recent years, due to the massive discharge of urban and rural sewage, oil and industrial pollution has become increasingly serious, water eutrophication has also intensified, red tides have occurred frequently, the area has gradually expanded, and aquaculture diseases have become increasingly serious, resulting in increasing losses, which has seriously damaged the aquaculture production environment in this water area. Therefore, the development of mariculture in China will be limited to a certain extent if we do not look for aquaculture methods and technologies that are far from the shore, can exchange water for water in deep water and have good self-purification conditions. The cage culture technology that can resist wind and waves can meet this requirement. Because of the different types, designs and performances of seawater cages, fish can be raised in shallow coastal waters as well as in deep water and open waters far from the shore, which greatly expands the culture space and greatly reduces the losses caused by pollution and intensive culture.
(two) effectively supplement the fishing output of marine fish.
China is the largest fishing country in the world, and 1989 has always been listed as the largest fishing country in the world. Of the total output of aquatic products of 3288 1096 million tons, marine fishing output/kloc-0.249 million tons, accounting for 37.9%; Among them, the fish output is 8.053 million tons. Of the total output of 8.24 million tons of marine fish in that year, the output of marine fish culture was only 6.5438+0.82 million tons, accounting for only 2.3%. By 2000, the output of marine fish culture in China was only 427,000 tons.
In recent 10 years, due to the continuous progress of China's marine fishing technology and equipment, the rapid increase of fishing boats and horsepower, the rapid expansion of fishing teams and the continuous destruction of the environment of economic fish spawning grounds, the amount of marine economic fish resources has dropped sharply, resulting in no closed fishing period, large-scale production and serious miniaturization of fishery products. To this end, our department has implemented the "zero growth" strategy of marine fishing since 1999, and strengthened the fishing moratorium system in summer. However, the implementation of these two measures did not fundamentally improve the marine fish resources, and the effect of fishing in summer was also consumed by the fishing in that year. It can be predicted that marine fishery resources will not be greatly improved for a long time to come. On the contrary, with the growth of population, the continuous improvement of people's living standards and the needs of fishery trade at home and abroad, the market demand for marine fish will still increase. An effective way to solve this contradiction is to develop marine fish culture, in which cage culture is one of the important ways.
(3) It is an effective way to encourage fishermen to change careers.
In order to realize the "zero growth" strategy of marine fishing and strengthen the fishing moratorium system in summer, reducing the number of ships and staff is one of the necessary measures; In addition, the demarcation of the northern waters has greatly reduced the traditional fishing areas in the South China Sea, and a large number of fishermen need to change careers, which requires the society to provide new opportunities and ways for fishermen to disembark. At present, the problem of fishermen's job transfer has brought great pressure to governments at all levels and fishery authorities in coastal provinces and cities, because it is not only related to the production and life of fishermen, but also to the social stability of fishing villages. Because these fishermen have been engaged in marine fishing for a long time, they have no basic means of production such as cultivated land on land, and the beaches or shallow water surfaces of their villages have already been dug up and contracted to others. Getting off the fishing boat means losing production conditions and urgently seeking new ways of production and employment. However, the shallow sea area in China is as much as 1. 1 100 million mu. Except for the coastal areas, most of them have been developed and farmed, and the waters farther offshore are still virgin land to be developed. Therefore, by vigorously developing cage culture technology, especially the seawater-tolerant cage culture technology, this part of land resources can be effectively developed and utilized, and new production and living space can be provided for fishermen who disembark, and they can smoothly realize the transformation of production and jobs.
(d) This is a good way to encourage fishermen to increase their production and income.
Since the reform and opening up, with the rapid development of China's economy, the continuous improvement of people's living standards and the prosperity of tourism, China's aquatic products market has developed rapidly, and the market demand for marine fish has continued to grow at a high speed, and gradually changed from chilled products to fresh consumption, which has become a new bright spot in the current aquatic products market. On the contrary, due to the depletion of marine fishery resources in China, the catch of high-grade and economic fish has fallen sharply, far from meeting the market demand, and the contradiction between supply and demand has become more prominent. A large number of high-grade and fresh aquatic products need to be imported every year. However, the development of marine fish culture in China is relatively backward. By the year 2000, there were only 700,000-800,000 cages for marine fish culture, and the land industrialized culture area was 700,000 square meters, and the total output in that year was only 427,000 tons.
Due to the prominent contradiction between supply and demand, compared with freshwater fish and other bulk aquatic products, marine fish culture has greater added value. For example, the current pond price of PARALICHTHYS olivaceus is about RMB 0/00 per kilogram/kloc-while the breeding cost is only about 50 yuan, and the profit rate is 100%. The market price of turbot is about 300 yuan per kilogram, the breeding cost is about 100 yuan, and the profit rate is 200%. Except for a few species such as Pseudosciaena crocea, American red croaker and perch, the profit rate of most cultured species is above 50%. So cage culture technology is a good way to encourage fishermen to increase production and income.
2. What is the history and present situation of cage fish culture in seawater in China?
Cage culture began more than 100 years ago along the Mekong River in Cambodia. It is made of bamboo and wood and is mainly used for raising catfish and carp. It was Japan that first developed marine cage culture and successfully applied it to large-scale production. From 1930s to 1950s, it has become an important and distinctive fish culture method.
China's marine cage fish culture began in the late 1970s, and entered a stage of rapid development in the 1990s, with increasing species. Since the 1970s, Huiyang County and Zhuhai City of Guangdong Province have conducted the first experiment of fish culture in seawater cages, and more than 20 species such as grouper, snapper and sea bass have been stocked, which has been successful. After 198 1 year, commercial fish were mainly sold to Hong Kong and Macao, and remarkable economic benefits were achieved. During the period of 1984, it developed rapidly in the coastal areas of Guangdong, and then it developed seawater cage fish culture in Pingtan, Fujian and Xiangnan, Zhejiang, and gradually moved to the northern coastal areas. According to incomplete statistics, by 1993, the number of fish cultured in sea cages in Guangdong, Fujian and Zhejiang provinces exceeded 57,000, with more than 40 species of fish, and the aquaculture output was nearly 6,000 tons. With the development of production, the total number of seawater cages in China has reached more than 20 by 1998; By 2000, there were more than 700,000 sea cages in China, close to 800,000, including 450,000 in Fujian Province alone. The average output per square meter is 20-30 kilograms. However, due to the lack of research on cage materials, structure and wind and wave resistance, at present, seawater cages in China can only be cultured in some inner bays or inshore with less wind and waves.
In order to solve the problem of resisting wind and waves, Guangdong, Fujian, Zhejiang, Shandong and other provinces have introduced overseas (Norway, the United States, Japan, Denmark and Taiwan Province Province of China) deep-water cages with strong anti-wind and waves for aquaculture experiments. At the same time, the research on the localization of anti-wind and wave deep-water cages has also begun, and it is expected that this difficulty will be overcome in the near future.
3. What are the types and structures of seawater cages in China?
Although the history of deep-water cage fish culture in China is not long, many beneficial explorations have been made in the material, structure and performance of cages. At present, there are many kinds of sea cages, which are different because of different classification basis. For example, according to the size of cages, they can be divided into small cages (4-20 square meters), medium cages (20-50 square meters), large cages (50- 100 square meters) and super-large cages (100-400 square meters). According to the shape of the cage, it can be divided into square cage, circular cage, polygonal cage and biconical cage. According to the combination form, it can be divided into single cage and combined cage; According to the fixed form, it can be divided into floating cage, fixed cage, overturning cage and sinking cage.
(1) floating cage
In this kind of net cage, the net clothes are hung on the floating frame, and the net cage floats on the upper water surface with the buoyancy of the floating frame, and the net cage drifts with the current, so as to ensure that the fish culture water body remains unchanged. This kind of cage is more convenient to move, and its shape is mostly square and round.
At present, the cages used in marine fish culture in China are mainly floating cages, including two types: one is a wooden combined cage popular in southern China and suitable for use in less stormy seas such as inner bay; Secondly, triangular steel cages suitable for offshore use are mostly used in northern China. Its basic structure consists of floating frame, box (net blanket) and sinker.
1, floating frameA floating frame consists of a frame and a floating frame.
The cages in the inner bay mostly adopt the combination of plane wood structures in Southeast Asia. For example, this framework is popular in Fujian, Guangdong and Hainan. This cage is usually composed of 6, 9 and 12, and each cage is a 3 m× 3 m frame. The frame is connected by 8 cm thick and 25 cm wide wooden boards, and the joints are fixed with iron plates and large screws. Two 50cm× 90cm cylindrical foam plastic floats (buoyancy 150kg) are added to each cage outside the frame, and one float is added to each side (3m long) in the cage. The upper edge of the frame is about 20 meters above the water surface.
Because the offshore cage is more stormy than the inner bay, the frame structure adopts triangular steel structure (Figure). Each side of the frame consists of three galvanized pipes of 1.2 or 1.5 inches, the cross section of which is triangular, and the four sides are connected to form a whole square. The side length (inside) is 4, 5 and 6 meters. Two floats with buoyancy of 150kg are evenly placed on both sides of the 4m× 4m frame. The top of the cage frame platform used by Yantai Aquaculture Company 1986 in Shandong Province is welded with 2-inch galvanized seamless steel pipe, with the length and width of 10 m respectively. The bottom of the platform is made of two 2-inch galvanized pipes welded in parallel, with a distance of 0.5m and a platform height of 0.45m. The top frame and the bottom frame, and the two galvanized pipes of the bottom frame are connected by 1 inch galvanized pipes. A 0.5-meter-long 1 inch galvanized pipe is vertically welded on the top frame as the pillar of the escape net. Floats are also Ф ф50cm×90cm cylindrical plastic foam floats, with 5 floats on each side and 20 floats on the * *.
2. Boxes, that is, netting, are made of nylon, polyethylene or metal (iron, zinc and other alloys). In China, polyethylene mesh (about 14 strands) is mostly used for weaving. The horizontal shrinkage coefficient is required to be 0.707 to ensure the net to open in water. You can make a single knot by hand or buy it from a net factory.
The shape of the netting varies from frame to frame, and the size should be consistent with the frame. At low tide, the net height varies with the water depth, generally 3-5 meters.
The mesh should be determined according to the size of the breeding object, and the material should be saved as much as possible to achieve the highest exchange rate of cage water. The principle is that it is best to break a mesh and not leak the net. The overwintering fry of red snapper weighing 50- 100g can use a mesh of about 3 cm. When the fish grows to about 200g, the mesh can be increased to 4.5-5cm.
There are two kinds of netting: single and double. Generally, single layer is used, which has smooth water flow and convenient operation, but it is not safe. Double-layer net generally has a smaller inner layer and a larger outer layer to facilitate smooth water flow. In the sea area with many crabs and dolphins, double nets should be used to prevent fish from escaping.
The net clothes are hung on the frame, generally 40-50 cm above the water surface. If necessary, a net can be added at the top of the cage to prevent fish from escaping and enemy attacks.
The net clothes are assembled by net pieces, and some are sewn by 6 net pieces, among which the net pieces have larger meshes. Some also fold a long net into a net wall, then sew the bottom of the net and cover it. Around the cage, as well as the upper and lower periphery, it should be reinforced with a certain thickness of steel mesh. The upper circumference is matched with the frame and fixed on the steel pipe of the inner frame of the frame with polyethylene rope. Finally, the underframe is installed at the bottom of the cage.
3. Lead or stone sinkers should be tied to the bottom of the sinker network to prevent the cage from being deformed. Generally, the sinkers of marine fish cages are equipped with a bottom frame 5 cm smaller than each side of the upper frame around the bottom of the net. The underframe can be welded with L-L.2 inch galvanized pipes, or several bricks or stones can be tied at the four corners of the underframe to adjust the gravity.
(2) Fixed cage
Suitable for bays with small tidal range. The cage is fixed on a cement pile inserted into the bottom of shallow sea. So don't go with the flow. But the volume of water in the water tank changes with the fluctuation of water level. The shape of the cage will not be deformed by the influence of current.
(3) Reversible cage
It is a fixed cubic frame made of iron pipes, angle irons or bamboo, with six sides covered with net clothes and one side left with an openable door. The whole cage can rotate around the axis. This kind of cage is characterized by its small size and convenient washing of attached weeds. The shape is fixed and will not be changed by the current. When in use, one side of the net cloth is exposed out of the water, and the weeds at the bottom of the net are easy to clean after drying. Turn over every once in a while, so that the four sides of the cage are exposed to the sun in turn, so as to clean up weeds on time. This can reduce the number of network changes. When in storm warning, it can be completely submerged in the sea to avoid the storm.
(4) Underwater cage
The whole cage is submerged in seawater, and the bait net opening is left at the upper part. The cage is located in the middle of the water layer, and the amount of water in the cage is constant, so it is not easy to be damaged when the wind and waves attack. Can be used for wintering warm-water fish or cold-water fish in summer.
(5) Floating rope cage
Floating rope cage is a kind of seawater cage form that only appeared in recent two years. It is an improved floating cage, which has stronger wind and wave resistance than floating cage. This cage consists of rope, cage, float and iron anchor. It is a flexible structure, which can fluctuate with the fluctuation of wind and waves. Secondly, the cage is a six-sided closed box, which is not easy to be submerged by the wind and waves, so that the fish can escape.
The flexible frame consists of two nylon ropes with a diameter of 6-8 cm and a length of 1 10 m or PVC ropes with a diameter of 10 cm as main cables, and 20 nylon ropes with a diameter of 3 cm and a length of 7 m as auxiliary cables to form a group of 10 cage frames, and then nylon ropes with a diameter of 2-3 cm are used. It is fixed on the main and auxiliary cables of the vehicle frame, and the spacing between the floating bodies is 40-45cm, and a large floating body is fixed at both ends of the main cable.
4. What kinds of farmed fish are there?
In the late 1970s, when fish were cultured in seawater cages in early China, most of the cultured species were caught in natural waters, including more than 20 species of grouper, snapper and sea bass. During the Tenth Five-Year Plan period, in order to select fish species suitable for cage culture in seawater and provide artificial fry in batches, the relevant scientific research units have successively released grouper, large yellow croaker, red snapper and black snapper. Generally speaking, all species suitable for pond culture can be cultured in cages. So far, there are more than 40 kinds of fish cultured in sea cages, both wild and artificial. Among them, the main cultured species are: red grouper, blue grouper, red snapper, black snapper, perch, large yellow croaker, fish-free yellow croaker, black snapper, flounder, white fish, cobia, yellow fin snapper, six-line fish and pointed nose. Fish, Brachydanidae, Rainbow Trout, Silver Salmon, Tilapia, Scophthalmus maximus, Ghost Fish, Acorus calamus, Six-fingered Bamboo Podfish, Mullet, Barracuda, American Red Crocodile, Giant Grouper, snapper, Red snapper and Red snapper.
Up to now, it is still mainly to cultivate wild seedlings, and there are not many kinds that can produce seedlings and provide artificial seedlings.
5. What are the problems and countermeasures of cage fish culture in seawater in China?
As far as the current technical equipment and technical level are concerned, there are still many problems in marine cage culture technology in China, and corresponding measures should be taken to solve these problems, so as to shorten the gap between China and developed countries, promote the development of marine cage fish culture in China, and promote the current fishermen to change their jobs.
(1) Strengthen the research and development of anti-storm cage equipment and facilities, and realize localization as soon as possible.
At present, seawater cages in China are all carried out in coastal shallow seas and harbors. Because of the poor wind and wave resistance of cages, it is difficult to breed in semi-open water, open water and other stormy waters. However, the price of imported anti-storm cages is very high, which is unbearable for ordinary production units and individuals. Therefore, on the basis of introducing and absorbing foreign advanced technology, we must speed up scientific research, realize localization as soon as possible, and develop domestic products suitable for China's national conditions and economic affordability.
(2) Organizing the research on the breeding technology of productive fry of mariculture fish to meet the needs of the development of mariculture.
At present, the species of marine fish are mostly wild species, which can not meet the needs of the development of marine cage fish culture in China because of their different growing places, different sizes, uneven number of fry and difficulties in artificial domestication. Therefore, we should vigorously organize scientific research to solve this problem as soon as possible.
(3) Vigorously organize the research on the development and application of nutritional feed for mariculture fish, and promote the development of mariculture in cage.
The research on nutrition and feed of marine fish started late in China. So far, only a few cultured species, such as PARALICHTHYS olivaceus and red snapper, have solved the feed problem, and most cultured species still feed on wild miscellaneous fish, which not only increases the breeding cost, but also seriously pollutes the water quality, which is not conducive to the development of marine cage fish culture. Therefore, we should vigorously organize scientific research to tackle key problems and realize the commercial breeding of pellet feed as soon as possible.