10. EXTENSIVE FISH CULTURE IN RESERVOIRS

China is said to possess approximately 2 million hectares of artificial lakes - or reservoirs - two-thirds of which are said to be used for extensive fish culture. Efforts have recently been made to extend the areas being exploited. In 1978 therefore, 1 208 427 ha of reservoirs were being managed (Zhu De-Shan, 1980), while in 1975 the figure was 1 254 040 ha, i.e., an increase of 3.77 percent (45 613 ha) in one year (Song, pers. comm., 1980). As extensive farming of these water areas developed, fish culture in cages became more widespread (Section 11.1).

Chinese reservoirs are classified either according to their capacity (for irrigation), or according to their surface area and are divided into three categories similar to those used for natural lakes (Section 9.1) ¹. Development and management are also group activities and are done either by the State (e.g., district or municipality), or by one or several people's communes. The same groups deal with both development and management.

Every reservoir is designed for multiple and integrated uses. The purpose of the Qingshan Reservoir (developed and managed by the Municipality of Hangzhou, Zhejiang) was mainly to regulate the flow of the river and at the same time, to produce hydro-electric energy (Table 35). In addition, however, the valley downstream (Figure 57) was developed so that the turbine reject water could be used for the irrigation of agricultural crops and for feeding an intensive fish culture centre (Section 7.2). The reservoir is used for the transport of products, production of stocking fry in cages (Section 5.4) and pens (Section 5.5) and for the production of food-fish.

Development of the reservoirs for fish culture purposes generally consists of:

1. Installing a protection net upstream from the turbine water inlet pipe (Figure 58);
2. Constructing barriers to prevent the fish from escaping into the tributaries, and
3. In small reservoirs only, preparing the bottom before flooding (either partial or over the whole area), in order to facilitate later fishing operations: removal of trees, removal of obstacles, such as tree stumps and large rocks, levelling.

Fish culture management in reservoirs is also fairly restricted. Stocking and fishing are the two principal activities. The two major problems at the moment consist of controlling ichthyophagic fish and fishing technology. At the Qingshan Reservoir, fishing is done in spring, using gillnets (harvesting common and crucian carps) and in winter, using a fykenet at a depth of up to 13 m (bighead and silver carps). At the Bailianhe Reservoir, on the other hand, fishing is done once a year, in autumn and only fykenets are used. When stocking is not carried out, little fishing is done. On the other hand, floating cage rearing is practised on a large scale (Section 11.1).

Chinese technicians consider that fish yields in reservoirs are generally lower by about a third than those in natural lakes of the same size. In 1978, the national average yield was 90 kg/ha (Table 8). Yield however varies from reservoir to reservoir. In the absence of planning and management, the very large Bailianhe Reservoir (41 300 ha) produces only 12 kg/ha/year, while the large Miyun Reservoir (9 300 ha), which is stocked once a year produces 150 kg/ha/year (Table 35). The Qingshan Reservoir (1 800 ha), which is well managed, gives a maximum annual yield of 870 kg/ha. Chinese reservoirs are therefore thought to have a high production potential and to achieve it fully, surveys must be carried out on a large scale.

1 A reservoir classification better suited to fish culture was recently proposed by Song (1980): more than 1 000 ha (large; 100–1 000 ha (medium); less than 100 ha (small))

Table 35

Extensive fish culture in some reservoirs

^a Reference ADCP, 1979; with green fodder and pig manure totalling 600 t/year
^b Reference Tapiador, et al., 1977

Figure 57 Integrated development of the lower valley of the Qingshan Reservoir (Zhejiang): re-utilization of turbine reject water for crop irrigation and pond fish culture. In the foreground, a feed canal crossing the valley

Figure 58 Protection net upstream from the turbine water inlet pipe at the Qingshan Reservoir, Zhejiang

The study group was able to visit two reservoirs during their tour (Table 35). The Qingshan Reservoir (Zhejiang) was built in 1960. Its maximum capacity is 200 million cubic metres. Before flooding, only the largest trees were removed. It is well managed by the Hangzhou Municipality and gives an excellent fish yield. The water level varies between +31.7 m (July-September) and +16 m (November-January), i.e., a maximum annual range of about 15.7 m. The Bailianhe Reservoir (Hubei, Figure 59), built in 1959 on the Xi Shui, is a large body of water of 413 km², the level of which may fluctuate by 18.5 m annually. This river is exploited jointly by three districts, including the Xishui and Yingshan districts. The Huanggang Prefecture is in charge of management, which however does not cover extensive fish culture. Fishing is not very developed and efforts are concentrated on cage production of fish (Section 11.1).

Figure 59 Study group briefing prior to visit of the Bailianhe Reservoir, district of Xishui, Hubei