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7. INTENSIVE FISH CULTURE IN PONDS

7.1 Experiments in Intensive Fish Culture

Pond production of food-fish using an intensive farming system, based on artificial feeding, is currently becoming increasingly wide-spread in China. When the study group visited the Institute of Aquatic Products of Shanghai (Section 4.1.2), this was stressed by the technicians involved in research on the subject.

The Municipality of Shanghai (10.8 million inhabitants, 50 percent of which are city dwellers) suffers from a scarcity of fish, in spite of the strides made in marine fisheries (240 fishing vessels), which produce 90 percent of the tonnage marketed today (200 000 t/year). The municipality wishes to develop urban industrial fish culture. Three types of systems of intensive culture are under review: an open system and a system involving partial or complete recycling of the water. To reduce the length of the production cycle, experiments have been carried out for the past two years using hot water wastes (25–28°C) from hydro-electric plants and annual outputs totalling 300 t/ha have been obtained. It is planned to use this in the near future on a pilot scale in 1.33 ha of cement pond.

Figure 48

Figure 48 Cleaning a pond and removing a layer of silt (Photo F. Botts)

It is also planned to practise intensive farming in 67 ha of pond. With this is mind, complete, balanced fish feed have been developed from by-products which are available in larger quantities in the region of Shanghai: rice and barley bran, soy bean cake and fish meal. Dry granules containing 22–42 percent protein have been developed for intensive rearing of grass carps (floating granules) 1 and black carps (non-floating granules) with nutritional quotients in the region of 2.5-3. Stocking density is 2.5-3 specimens/m2 (equal to 4 500 kg/ha). Artificial aeration at day-break becomes necessary as soon as the ichthyomass reaches 7 500 kg/ha. Average output varies between 15 and 22.5 t/ha/year.

Research is also underway at the Institute of Aquatic Products at Zhu Jiang, Guangzhou (Section 4.1.1). They are experimenting with intensive grass carp rearing in cement ponds of 4 m3 capacity with partial recycling of water. Specimens of an average weight of 250 g are stocked at a density of 80–100 specimens/m3. Water in the ponds is changed four to six times every 24 h. Dry granules are distributed at the daily rate of 2–4 percent of the biomass present. The protein content of these granules varies from 30 to 50 percent (young fish) to 20 percent (older fish) and their nutritional quotient is approximately 2.6. Green fodder is distributed (Qu 10–15) as supplementary feed. Grass carps grow by 750 g in 30 days and reach the final weight of 1 kg. Average output is therefore 40–50 kg/m3/month.

1 The study group watched floating granules being prepared for grass carps when they visited the ‘Liberation’ People's Commune (Qingpu district, Shanghai). They contained: wheat bran (30% dry weight); barley bran (25%); soy bean cake (15%); fish meal (15%); green fodder (10%) and maize (5%); final water content: 22%;cost price: Y 0.5/kg

7.2 Intensive Fish Culture on a Pilot Scale

The study group was able to observe the intensive farming system applied to a pilot production of either grass carps (Qingshan Reservoir) or Japanese eels (Hangzon).

Downstream from the Qingshan Dam, the Municipality of Hangzhou has set up a centre for intensive fish culture, which utilizes the water which feeds the turbines of the hydro-electric plant (Figures 37 and 49). Intensive production of grass carps weighing 1 kg, is practised every year during the hot season (May-October) when the temperature of the water is around 22–25°C. Sixteen cement ponds, each of a capacity of 24 m3 are stocked with 18 cm (40 g) fingerlings at a density of 125 specimens/m3, i.e., 5 kg/m3. These fish are fed several times a day with floating granules containing 20 percent proteins (cost Y 0.15/kg) at a daily rate of 3–4 percent of the biomass. Their nutritional quotient is relatively low. Green fodder is distributed as a feed supplement (Qu 10–15). In five months of intensive rearing, each pond produces approximately 2 700 kg of grass carps, which is equal to an average net output of 100–110 kg/m3, or an average 20–22 kg/m3/month.

Figure 49

Figure 49 Intensive farming of grass carps at the Fish Culture Centre of the Qingshan Reservoir, Zhejiang

The Hangzhou Aquatic Products Experimental Centre also utilizes wastes from a hydroelectric power station for intensive fish culture. Eels (Anguilla japonica) have been reared in warm water (24–27°C) since February 1980, the aim being to produce specimens weighing 150–200 g (30–40 cm) in six months for export to Japan. The total surface area used is 2 733 m2, 633 m2 of which is under glass (Figure 50) and the rest in the open air, as follows: 3 cement ponds 51 m2 each and 4 cement ponds, 120 m2 each (under glass); 4 round ponds of 260 m2 and 2 round ponds of 530 m2 (outdoor). Elvers (0.12–0.14 g) from the briny waters of the province, are stocked in the smallest basins at a rate of 0.5 kg/m3. When this rate reaches 2 kg/m3 after about 20 days rearing, the young eels are sorted by size and transferred to ponds of twice the capacity. The initial stocking rate is again 0.5 kg/m3. When the biomass reaches 2 kg/m3, the eels are once again sorted and transferred to larger ponds. The same procedure is repeated a third time, until the final harvest is carried out in the largest ponds. Feed, based on fishmeal to which vitamins are added (cost Y 2/kg) is distributed, shielded from the light, in the form of a paste, at a daily ration of 6–8 percent of the biomass. A nutritional quotient close to 2 is expected. Water recirculation is important. A dissolved oxygen content of at least 60 percent of the saturation rate is maintained by means of a supply of compressed air and, if necessary, by means of floating paddle aerators. During the annual rearing cycle a gross output of 28 t of eel can be expected in six months, i.e., an average of 10.25 kg/m2.

Figure 50

Figure 50 Intensive eel farming at the Hangzhou Experimental Centre, Zhejiang. View of one of the cement ponds under glass equipped with a floating aerator and a tent for artificial feeding


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