Freshwater Fisheries Research Centre, Wuxi 214081 China
Changchun Municipal Aquatic Products Research Institute, Changchun 130000 China
The authors reviewed the present status and the achievements of cage culture in China and evaluated its enhancement role in lake, reservoir and riverine culture with reference to data and survey reports during the period 1978–1996. The authors also indicated the constraints to the development of cage culture in China at the present time. In this 18-year period, the area of cage culture in China has expanded at an average annual rate of 71%. The fish production from cage culture increased year by year. During the period 1978–1993, fish production of cage culture per ha increased by an average of 9.8% per annum. A variety of species is being cultured in cages. Special aquatic products have been successfully cultured in cages in recent years, increasing economic return of cage culture. Cage culture is adaptable to various inland water bodies and is an effective way to utilise and develop inland water resources.
Cage culture originated in the middle reaches of the Yangtze River in China some 800 years ago (Hu, 1994). Since the 1970s, culture techniques have been improved through the introduction of some advanced techniques of cage culture from other countries (Hu and Lu, 1980). This has led to the boom in modern cage culture in China. In compliance with the natural ecological environment of inland water bodies, Chinese cage culture has its own characteristics (Hu, 1994). Nowadays, cage culture is widespread throughout densely inhabited southern and eastern China.
In the last two decades, Chinese cage culture techniques have been extended and developed. Cage culture effectively promotes utilisation and development of inland water bodies in China. The fish yields in reservoir, lake and riverine culture are increasing year by year. It changes the cultivated species and culture structure of traditional inland fisheries. In 1985 and in September and October 1986, the authors visited Jiangsu, Zhejiang, Hubei, Hunan, Shanxi, Sichuan, Jilin and Beijing and investigated 16 lakes and reservoirs, and interviewed staff from the relevant institutions and collected a great deal of useful data. Using the collected information, this paper reviews the present status, achievements of and constraints to cage culture in China and comments on its enhancement role in inland fisheries.
2. PRESENT STATUS AND PROBLEMS OF CAGE CULTURE IN CHINA
2.1 The progress in cage culture in China
In 1978, the area of cage culture in China was only 15.13 ha. In 1990, a comprehensive survey showed that the area of cage culture in the country reached 533.3 ha. The total fish production from cage culture was 159,990 tons, which accounted for half of the fish production from large inland water bodies and indicated the importance of cage culture in inland fisheries. In 1991, the area of cage culture reached 540 ha; by 1996, it was about 1300 ha.
In the early 1990s, the Freshwater Fisheries Research Centre introduced small volume high-density cage culture techniques from the USA The highest unit production reached 187.5 kg/m3. This was a big advance in cage culture.
Prior to 1980, the dominant species cultured in cages were traditional ones, but in the 1990s the cultured species changed to more specialised aquatic products. Eel cage culture proved successful in medium- and small-sized reservoirs. The survival rate of nurturing eel fry to fingerlings reached 92.7%–94.5% (Zhao and Wang, 1994) while that of rearing eel fingerlings to commercial eel products reached 96.5–98% (Chen et al., 1992). The cost of producing one ton of eel in cages was 22.1% lower than in ponds. In 1987, mandarin fish Siniperca chuatsi monoculture first succeeded by using 5×5×2 m open cages in Fuqiaohe reservoir in Hubei Province. The key was to find live feed for mandarin fish. They utilised palatable fingerlings of bighead carp Aristichthys nobilis to feed mandarin fish. The average food conversion ratio was 4.06:1. Liang (1994) studied the physiology of food intake behaviour of mandarin fish and the perception basis and mechanism of food intake behaviour, and then used this information to make the fish take dead fish and artificial feeds. In 1993, 9 trial cages with a volume of 2.4 m3 each were used to culture grow-out of mandarin fish in Fuqiaohe reservoir by feeding them either live fish, dead fish or chopped fish. All succeeded. Fingerlings with an average body weight of 176 g were reared to 568 g, 428 g and 473 g market size mandarin fish with the FCR 4.0, 4.9 and 4.4, respectively, on the above diets. Leiocassis longirostris from the Yangtze River is another example. Cage culture of this species has also had preliminary success (Wu and Zhang, 1996). In lakes, there has been a rapid development in cage culture of shrimp Macrobranchium nipponensis, Chinese mitten-handed crab (Eriocheir sinensis) and bull frog (Rana catesbeiana).
The range of aquatic products cultured in cages is increasing, but most are still fish species. Cage culture can be classified into four types in terms of feed sources:
Natural food organisms are used to culture silver carp (Hypophthalmichthys molitrix), bighead carp, tilapia, and some other species;
Commercial feeds are used to culture common carp (Cyprinus carpio), rainbow trout (Oncorhynchus mykiss), Japanese eel (Anguilla japonica), and a few others;
Live fish in assorted cages are used to feed mandarin fish;
Green fodders in integrated farms are used to feed grass carp (Ctenopharyngodon idella) and bream (Megalobrama amblycephala).
2.2 The problems of cage culture in China
There are 150,000,000 ha of inland water bodies, 90% of which are classified as large water bodies. The cultured area is less than 30%. The inland water resources are not fully utilised and still have great potential. One effective approach is to develop cage culture. However, the differences in production technology, human resources, investment, managerial level, market manipulation and economic efficiency among different areas can cause unbalanced development of cage culture.
2.2.1 Lack of technologies and qualified technicians
Technology problems are largely due to lack of qualified personnel. At the present time, most of the scientists, technicians, and technical workers engaged in cage culture have a good command of culture techniques of silver carp, bighead carp, common carp and grass carp and these techniques have already been standardised. But only a few are familiar with the culturing techniques of some special aquatic products, for which there is now a good market. These techniques have not been popularised. For example, cage culture using all-metal cages in running water is an effective technique to enlarge the utilisation area of rivers with rapid current. But it has not been popularised because of the technical skill needed to install such cages.
There are two solutions to these problems: in the long term, culture techniques are incorporated into the curriculums of fisheries colleges; in the short term, various short-term training courses could be organised to extend the techniques of culturing special aquatic products to meet the demands of the market. Such training courses should be on -farm, where cage culture is practised successfully. This will get better results.
2.2.2 Capital and management
The development of cage culture needs great amounts of capital input. Under the present financial conditions, the state can not afford to invest large amounts of money to develop cage culture. Therefore, the investment from individuals and communities is encouraged alongside the state ownership. The solution for financial constraints of cage culture depends on individuals, communities and the state, but mainly on fish farmers with benefits for themselves. The management relies on contract systems and production associations, as well as on guidance by professional technical personnel. The cage culture farm will be administered by the investors themselves and the scale of investment and cultured species could be adjusted according to the market demand. Experience has shown that this is the most promising way to develop cage culture in China.
2.2.3 Market manipulation and economic efficiency
Studies indicate that in northern China, the area of cage culture has been shrinking in some areas. The main reason is that the production from cage culture exceeded demand, resulting in no net profit. Jilin was one such province, where cage culture developed early. By 1992, there were more than 1000 common carp cages supplying fresh live common carp. Afterwards, prices of feeds, nets, etc. soared. The cost of production increased while the retail price of fish fell slightly. The more fish farmers produced, the more they suffered economic loss. By 1996, the number of cages had fallen to 100. The solution is to develop cage culture of special aquatic products for which there are strong markets. The culture must be market-oriented and have sound economic returns.
3. THE IMPACTS OF CAGE CULTURE ON THE DEVELOPMENT OF INLAND WATERS
3.1 To enlarge the scope of utilisation of inland waters
Rivers and streams criss-cross mainland China, few of which are fully utilised for fishery development. Following introduction of running water metal cage culture techniques, fish production in riverine culture increased significantly. In 1978, the area of riverine culture reached 281,500 ha in China. By 1993, utilisation had increased by a further 27.86%. Fish yields increased from 308.5 kg/ha in 1978 to 980 kg/ha in 1993, an increase of 217.7%. Total fish yield, which was 80,676 tons in 1978, was increased by 306.3%. The average annual rate of increase over 15 years was 9.8%.
Nowadays, the main form of utilisation and development of rivers, streams and canals is cage culture. According to Liu Hanyuan et al. (1990), the optimal size of metal cage is 10–15 m long, 2–5 m wide and 2–3 m high. The optimal rate of flow should be kept within 0.05–0.2 m3/second. Thus rivers, irrigation and drainage channels of hydropower stations and streams in hilly areas with appropriate current speeds could be used for cage culture.
China also has some downstream lakes with large fluctuations in water level. It is always difficult to use this kind of water body. For example, in Lake Gucheng and Lake Shejiu in Jiangsu Province, water levels fluctuate between 12.8 m and 5.5 m. In a normal year, there is a 5.5 m fluctuation. Cage culture provides an effective way to utilise the lakes. Mandarin fish and bighead carp culture in cages succeeded in Lake Shejiu and Lake Gucheng, respectively. The fish yield of bighead carp in cage culture, which fed on natural food organisms, reached 11.7 kg/m3 of water.
3.2 To increase the utilisation rate of inland fishery resources
Fish yields in lakes, reservoirs, rivers and canals increased from 200,032 t in 1978 to 247,398 t in 1993 with an annual rate of 31.57 tons. In those fish yields, cage culture has played an important role. Cage culture of filter-feeding fish can utilise natural plankton in eutrophic reservoirs. In such situations high yields of both fingerlings and table-sized fish of silver carp and bighead carp can be produced (Hu and Min, 1984; Hu 1994). The leftover feed in cages fertilises the ambient water body and promotes an increase in the fish yield of the whole lake. The total fish yield in Lake Jinyang (Shanxi Province) doubled as a result of cage culture. In lakes with aquatic macrophytes, cage culture uses herbivorous fish. 80 –100 kg of aquatic macrophytes are sufficient to produce 1 kg of fresh fish. Thus, the yield of herbivorous fish may range from 75 t to 325 t/ha. The open waters of large water bodies provide a better growth environment for cultivated fish, so fishery production is often high. If pelleted feeds are used to culture common carp in cages, fish yields can attain levels of 50–100 t/ha. In 1990, as mentioned before, the total production from cage culture accounted for 67.53% of the total fish production of lake, reservoir and river culture.
3.3 To change the fishery structure in open waters
3.3.1 To change the traditional fingerling production method
Stocking in open waters needs a great number of fingerlings. Prior to the 1970s, most of fingerlings stocked into reservoirs and lakes came from pond culture. Inadequate, small-sized fingerlings and lack of variety hampered the increase of fish yields. After the extension of cage culture techniques, the problem of rational stocking of fingerlings in open waters could be solved by adequate supply of fingerlings reared in cages (Hu, 1994). For example, summerlings, one-year and two-year fingerlings of silver carp, bighead carp, grass carp, bream and crucian carp (Carassius auratus), which were reared in cages, were stocked into Qingshan reservoir in Zhejiang Province. Fish yields increased from 585 kg/ha in the 1970s to 840 kg/ha in the 1980s. Per unit production increased by 43.6% and the production value and profit increased by 30% and 55%, respectively (Wang and Zhu, 1990). In many reservoirs such as Xinanjiang reservoir and Fuqiaohe reservoir, traditional pond-based method of rearing fry and fingerlings was replaced by cage culture.
3.3.2 To change the traditional cultured species
The species structure of inland fisheries is currently undergoing readjustment. This is due to the development of cage culture, which has resulted in the following developments.
Monoculture is practised in line with the local aquatic ambience, e.g. metal cage culture can be installed in cold water streams to culture rainbow trout.
The range of cultured fish species is being enlarged from common species to various special, unique and quality species so as to open new ways of increasing the profitability of fish farming.
3.3.3 To change the traditional management mode
Open waters can be divided into different production areas according to natural environment, social conditions and fishery economic status, e.g. Lake Gehu and Lake Changdong in Jiangsu Province are divided into three different ecological areas: cage and pen culture area, enhancement area and reproduction protection area. By applying this approach to management, fish yields in Lake Changdang increased by 25% between 1986, when the simultaneous development of aquaculture and fishing was practised, and 1995.
4.1 How to raise the fish production
In nearly 18 years, the area of cage culture expanded by an average annual rate of 71.38%. Small-volume cage techniques with cages measuring 1×1×1 m or 2×2×1 m have been extended in inland waters since 1993. In that year, cage culture achieved 8000 m 3 and in 1994 the area of cage culture increased by 87.5%. In 1995, cage culture techniques were extended to more than 20 provinces or regions such as Anhui, Shanxi, Fujian, Shadong, Qinghai, Shaanxi provinces and Inner Mongolia and Ningxia autonomous regions, and the volume of cages increased by a further 48.8%. The fish yields increased from 1500 t in 1993 to 2879.9 t in 1995 solely from small-volume cages.
The greater the area of cage culture, the higher the productivity. In the 1970s, the productivity of cage culture was about 8–10 kg/m3; productivities increased to 10–15 kg/m3 in the 1980s and 15–20 kg/m3 in the 1990s. There is still a potential increase in cage culture because the average fish yield of cage culture is far from the production records (172.5-167.5 kg/m3) of cage culture in China. The extension and intensification of cage culture is one of the most important means of increasing production in inland fisheries.
4.2 How to increase the economic benefits
In northern China, the supply of common carp exceeds the market demands because of cage culture. Moreover, the rising cost of material such as feeds and nets has led to only a small difference between the market price of common carp and the cost of farming in cages. In southern China, the economic return of cage culture of common species is dropping. This promotes an increase in the diversity of cultured species and intensification of cage culture. Thus, special aquatic products are produced in cage culture.
Liu and Xiao (1993) used cages to culture large-mouth black bass (Micropterus salmoides), gaining 30–74 yuan from each square meter. Wu and Zhang (1996) used cages to culture Leiocassis longirostris, gaining profits and taxes of 600 yuan from each square meter. Chen Heqing et al. (1992) used cages to culture Japanese eel, with a profit gain of 167 yuan from each square meter.
In order to raise the economic return of cage culture of common species, Wen Changchun et al. (1993) adopted small-volume high-density cage culture techniques. The productivity of 202 cages reached 187.5 kg/m3. Profits and taxes for each cubic meter of water were 500 yuan, three times the economic return of cage culture in situ. Culture of high value aquatic products and raising the productivity from water bodies are two conditions for higher economic returns from cage culture.
4.3 The use of combined cage culture for increasing fish production
Although Hu and Min (1984) raised the question of the carrying capacity of reservoirs, too many cages were placed in certain reservoirs, resulting in cultural eutrophication. For example, in Jintang reservoir, Sichuan Province, the fish yield of common carp reached 150.33 t from cage culture. The plankton and detritus conspicuously increased. Subsequently, two measures were taken: (1) to strictly control the area of cage culture; (2) to rear fingerlings of silver carp and bighead carp and then to stock them into the reservoir. The results indicated that the annual fishing yield on average reached 28,880 kg, 29.2% higher than the previous two years, a 25.7% increase in economic return per unit stocking area. The yields of silver carp and bighead carp accounted for 72.8% of the total fish production, while water quality was also improved.
The optimisation of cage culture production may be enhanced through the combination of: fry cages and grow-out cages of the same fish species; of filter-feeding fish cages and pellet-feeding fish cages, of table-sized fish producing cages and carnivorous fish cages; and of fingerling-rearing cages and fish enhancement in open waters. For this purpose, it is necessary to study systematically hydrology and water quality, food organisms and fish resources of different lakes, reservoirs and rivers. The constraints can be overcome one by one. The area of cage culture will be further enlarged. The economic return of cage culture will increase as well as the fish production. We are seeking a modernised path toward the implementation of cage culture, which may be a reference point for developing countries.
We would like to thank the production units of Jian gsu, Zhejiang, Shanxi and Jilin provinces for providing us valuable information. Special thanks go to the Information Centre of Chinese Academy of Fishery Sciences and the Aquatic Products Techniques Extension Station for providing valuable data.
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