Studies on the ecological effects of varying the size of fish ponds loaded with manures and feeds

Aquaculture, 60 (1987) 107-116 Elsevier Science Publishers B.V., Amsterdam

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Studies on the Ecological Effects of Varying the Size of Fish Ponds Loaded with Manures and Feeds F.L. ZHANG, Y. ZHU and X.Y. ZHOU Asian-Pacific Regional Research Center for Zntegrated Fish Farming, Wuri (People’s Republic of China) (Accepted

19 June 1986)

ABSTRACT Zhang, F.L., Zhu, Y. and Zhou, X.Y., 1987. Studies on the ecological effects of varying the size of fish ponds loaded with manures and feeds. Aquaculture, 60: 107-116. The major species of Chinese carp: grass carp (Ctenopharyngodon idella), bighead carp (Aristichthys nobilk), silver carp (Hypophthulmichthys molitrin), common carp (Cyprinus carpio) , crucian carp (Carassius auratus) , and Wuchang fish (Megalobrama terminalis) were cultured using the traditional Chinese polyculture system in different-sized ponds loaded with pig manures. The grass carp were given aquatic grass as supplementary feeds. Two experiments were conducted in 1982 and 1983 using nine fish ponds of sizes varying from 1 mu (667 m”) to 11 mu (7333 m*) , each for a culture period of 200 days. The average yield attained 6090 kg/ha. The conversion rate of pig manure and aquatic grass to fish biomass was found to average 1’7:l and 85:1, respectively. Results indicated higher yield obtained in pond sizes between 3 and 5.7 mu (1999 and 3800 m’) using standard pond management. Bigger ponds with greater surface area were more difficult to manage and often resulted in lower fish yields. The study also indicated that the fish yield in various experimental ponds was affected by the growth and survival rate of the grass carp, the main species cultured. Dissolved oxygen was found to be lower in smaller ponds and increasing frequency of ‘fish surfacing’ was noted, while other nutrient levels such as that of total nitrogen, ammonia, nitrite, and phosphate did not appear to have a direct effect on the fish yield. There was no direct relationship between primary productivity, organic detritus, and fish yield in different-sized ponds. However, production of filter feeders (silver and bighead carp) was higher than previously recorded indicating the optimal stocking rate in the polyculture system had been adopted.

INTRODUCTION

In this study, seven fish ponds of different sizes were assessed, in two trials. After two years of experimentation with pig manure and aquatic grass as feedstocks, a per-hectare yield of 6090 kg p.a. was achieved. The experiment characterises the following aspects: (1) the effect of pond size on fish growth and yield;

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(2 ) the economic nature of a fish/pig manure/green fodder farming system;

(3) the physical-chemical-biological

parameters of fish ponds.

MATERIALS AND METHODS

This experiment was conducted at the Wuxi Municipal Fish Farm, over a two-year period, encompassing 2 x 200 culture-days, from early 1982 into 1983. The principal feedstock was pig manure, supplemented with aquatic grass ( Vallisneria spiralis Linn., Najas minor All. and Potamogeton maluinus Mig. ) . The pond sizes assessed were as follows (based on the Chinese mu, 0.066 ha (15 mu=1 ha)): 1982,5 ponds - 667 m2 (1 mu); 1601 m2 (2.4 mu); 2068 m2 (3.1 mu); 3135 m2 (4.7 mu); and 3800 m2 (5.7 mu); 1983,4 ponds - 667 m2 (1 mu); 1601 m2 (2.4 mu) ; 3468 m2 (5.2 mu) ; and 7333 m2 (11.0 mu). Mean pond depth was 1.5 m in both years, except in July-September 1983, when, due to flooding, the 5.2- and ll.O-mu ponds were 2-2.5 m deep. The fish stocked in these two ponds were identical in species, density and size for the sake of comparison. Total stocking density was 15,00O/ha in 1982 and 18,00O/ha in 1983, subdivided as follows: 1982: silver carp 7500/ha, bighead carp 1550/ha, grass carp 4500/ha and common carp 1500/ha; 1983: silver carp 4500/ha, Wuchang fish 3000/ha, crucian carp 3000/ha; the other species, as 1982. Average individual stocking weights in both years were: silver carp 125 g, bighead 185 g, grass carp 200 g (310 gin 1983)) common carp 100 g,Wuchang fish 85 g and crucian carp 25 g. The annual pig manure load was 4800 kg/mu, with an average 24 kg for daily application. Annual input of feed (mainly aquatic grass) was 13,700 kg/mu, averaging 68.5 kg/mu for daily application. (It is commonly accepted in China that 1.0 kg of aquatic grass has a dry weight equivalent to 0.5 kg of terrestrial vegetable matter. ) Daily measurements were taken on the air temperature, water temperature, D.O. and pH. The determination of the water physico-chemistry was performed every two weeks; D.O. was analyzed by the Winkler method; ammonianitrogen (NH,-N) by the Nessler method; nitrite-nitrogen (NO,-N) by the Calorimetric method; nitrate-nitrogen (NO,-N) by the colorless nitro derivative method; phosphate (PO,) by the soluble orthophosphate method; COD, by the potassium dichromate method of titration; and BOD was incubated in the dark for 5 days at 20’ C. Plankton, chlorophyll-a and primary productivity were measured once or twice a month. Light and dark bottles were suspended separately at 25 cm from the water surface from 7 a.m. to 6 p.m. and the bottles were changed every two hours. Water samples were taken from different depths with a ladle or with a 5-l sampling bottle through a rubber tube. Phytoplankton was sampled with plankton net of 90 mesh/mm’ and qualitative analysis was

109 TABLE 1 Average dissolved oxygen (mg/l) Pond size m* (mu)

for 1982 experiments

(pH ranged from 7.42 to 8.20)

Month

667 (1.0) 2068 (3.1) 3800 (5.7)

July

Aug.

Sept.

Ott

2.0 3.5 3.7

1.8 2.8 3.1

1.6 1.7 2.3

1.7 2.1 3.6

made after fixation with 4% formalin. Zooplankton was analysed on live samples. For quantitative analyses 10 1 water were sampled under the water surface, 11 for the analysis of organic detritus and 11 concentrated into 30 ml and observed under the microscope for the count of protozoa and rotifera. The remaining 8 1 were filtered with the plankton net and fixed with 4% formalin for the count of cladocera and copepoda. Routine methods were adopted for the determination of the physico-chemical characteristics of water, (Tables 1 and 2) and a YSI-57 D.0. meter to measure D.O. with a reading precision of 0.01 ppm. A secchi disc was used to measure turbidity. The green feed and the manure applied in the experimental ponds were measured and recorded. A 3kW aerator was installed in each pond, while two 0.3 kW aerators were used in the 667 m2 pond. RESULTS

AND DISCUSSION

Fish yield During the two years of experiments, an average yield of 559.5 kg per mu was harvested; net gain after excluding the stocking weight of 153.5 kg was 406 kg/mu (Table 3 and Table 4). TABLE 2 Parameters Parameter

NH,+-N NO,--N N03--N PO:COD BOD

of water physico-chemistry

annual average (mg/l)

Pond size mu/m’ 1.01 667

3.11 2068

5.11 3800

0.93 0.077 0.044 0.04 12.69 6.18

1.09 0.12 0.103 0.033 11.08 0.05

0.73 0.01 0.02 0.04 11.75 5.97

for 1982 experiments

4.5 17.5 100.0 177.0 528.0 351.0

Stocking Harvest Survival

Stocking Harvest Survival

Stocking Harvest Yield (kg)

Wuchang fish

Crucian carp

Total

120.0 347.5 227.5

18.5 32.0 80.0

6.5 11.0 100.0

168.0 612.5 444.5

7.5 53.5 100.0

158.0 555.5 397.5

10.5 46.5 100.0

138.5 481.0 342.5

9.0 47.0 100.0

49.0 170.5 56.0

102.0 512.5 410.5

7.0 46.5 100.0

38.5 163.5 53.0 9.0 23.0 98.0

93.5 258.0 85.0

17.5 36.5 100.0

Stocking Harvest Survival

66.0 266.5 89.0

9.5 50.5 99.0

Common carp

SUNiVal

79.5 269.0 82.0

13.5 44.0 96.0

32.5 161.0 55.0

13.5 40.5 90.0

34.0 161.0 96.0

Stocking Harvest

Grass carp

survival

13.5 48.5 92.0

47.0 252.0 99.0

13.5 29.3 94.0

67.0 218.5 96.0

Stocking Harvest

68.0 202.0 90.0

Bighead

67.5 242.9 92.0

67.5 146.3 94.0

Stocking Harvest Survival

38Ow 5.7

177.0 528.0 351.0

4.5 17.5 100.0

18.5 32.0 80.0

9.0 23.0 98.0

93.5 258.0 85.0

17.5 61.0 100.0

31.0 236.0 97.0

2068/ 3.1

6611 1.0

31351 4.7

6671 1.0

2068/ 3.1

Pond size (ms/mu)

Pond size ( m’/mu) 1601/ 2.4

In 1983

In 1982

(kg) per 667 m* (mu ) ; ‘5% survival, and total yield

Silver carp

Fish species

Weight of fish stocked (kg) and harvested

TABLE 3

178.5 618.0 499.5

4.0 46.5 100.0

17.5 52.5 100.0

11.5 64.5 100.0

93.5 226.5 85.0

13.0 60.0 88.0

39.5 231.5 96.0

3468/ 5.2

163.5 563.0 400.0

3.5 34.0 100.0

16.0 40.0 80.0

12.0 67.5 100.0

89.0 185.5 66.0

13.5 36.5 66.0

29.0 299.5 93.0

7333/ 11.0

154.0 554.0 400.0

4.1 36.C 100.0

17.3 43.5 90.0

9.3 42.4 99.7

71.0 228.0 74.5

13.7 45.2 91.6

50.1 221.0 94.7

Avg.

Size at stocking Size at harvest PI.

Size at stocking Size at harvest PI.

Wuchang fish

Crucian

carp

carp

Size at stocking Size at harvest PI.

Size at stocking Size at harvest P.I.

Size at stocking Size at harvest P.I.

Size at stocking Size at harvest PI.

Common

Carp

Grass

Bighead

carp

Silver

Fish species

185.0 510.0 2.8

185.0 370.0 2.0

185.0 550.0 3.0

125.0 560.0 4.5

31351 4.7

185.0 560.0 3.0

170.0 130.0 520.0 525.0 3.1 4.0

175.0 365.0 2.1

3468/ 5.2

125.0 130.0 810.0 700.0 7.1 5.4

2068/ 3.1

115.0 560.0 4.9

667/ 1.0

Pond size ( m2/mu)

In 1983

(PI. ) in average sire

635.0 7.9

80.0

3800/ 5.7

increase

65.0 110.0 1.7

75.0 390.0 5.2

105.0 360.0 3.4

80.0 445.0 4.9

70.0 360.0 5.0

90.0 85.0 255.0 205.0 2.8 2.4

25.0 20.0 170.0 105.0 6.8 5.3

25.0 85.0 3.4

100.0 115.0 230.0 255.0 2.3 2.2

200.0 2.2

90.0

80.0 235.0 2.6

105.0 250.0 225.0 165.0 110.0 310.0 325.0 300.0 975.0 1095.0 1000.0 1010.0 1035.0 1010.0 1650.0 880.0 4.4 2.9 9.3 4.4 6.1 9.4 3.3 3.5

510.0 2.7

190.0

125.0 515.0 4.1

125.0 645.0 5.2

125.0 385.0 3.1

6671 1.0

20681 3.1

(m*/mu )

1601/ 2.4

Pond size

In 1982

Average stocking weight (g ) , average weight at harvest ( g) and proportional

TABLE 4

20.0 100.0 5.0

200.0 2.5

80.0

120.0 400.0 3.3

310.0 910.0 3.0

135.0 550.0 4.1

700.0 7.4

95.0

7333/ 11

22.5 115.0 5.1

86.0 215.0 2.47

90.0 309.0 3.4

233.0 1063.0 5.1

171.0 495.5 2.97

116.0 522.0 4.36

Avg.

112

In our experiment, silver carp and grass carp were two species determining the yield ranging between 350 and 600 kg/mu. The factors affecting the yield were the survival rate of grass carp, the manure and the feed. As for the other species, each resulted in an output of only around 50 kg/mu. A few problems related to the yield are discussed below. Stocking density

The stocking density and proportions of various species depend on the different farming methods. Here the stocking densities of all species are detailed in relation to the farming approach in our experiment. (1) Silver carp: 500/mu in 1982 and 300/mu in 1983. The yield range was 146.5-252 kg/mu in 1982, and 161-236 kg/mu in 1983. The market weight from 500 fish/mu was only 0.35-0.6 kg/per fish, while that from 300/mu was 0.7-0.8 kg, which is a more marketable size. The result of the two years’ experiment has thus indicated that the suitable stocking density for silver carp is 300,‘mu. (2) Bigheud: In the two years, the stocking density was 100 kg/mu with a yield of 50 kg/mu. The average harvested fish weight was somewhat too small for the market. It would be better, therefore, to reduce the density a little. In practice in China, the stocking proportion of bighead does not go beyond 20% that of silver carp. (3) Grass carp: 300/mu were stocked for the two experimental years. The yield range was 161-269 kg/mu in 1982, and 185.5-254 kg/mu in 1983. The stocking density was moderate. (4) Common carp: lOO/mu were stocked during the two years. At this density, the yield in 1983 was 23-67.5 kg/mu with the average marketing weight below 0.5 kg. Accordingly the stocking density should also be reduced. (5) Wuchang fish: The yield in 1983 was 32-52.5 kg/mu, with a body weight of 0.2-0.26 kg/per fish, which is a desirable size for the market. (6) Crucian carp: The yield in 1983 was 17.5-46.5 kg/mu. The experiment showed that a stocking density 200/mu with a yield of 50 kg is appropriate. Economic effect Conversion rate of manure and feed: The annual pig manure input was 4800 kg/mu averaging 24 kg for daily application. The annual input of feeds (mainly aquatic grass) was 13,700 kg/mu averaging 68.5 kg/mu for daily application. The pig manure conversion rate was 17:l (8.5 kg pig manure gave 0.5 kg fish meat) while the aquatic grass conversion rate was 85:l (42.5 kg aquatic grass gave 0.5 kg grass carp meat) ; for details see Table 5. Relationships between pond sizes and yields

The general case of the relationship between different pond sizes and fish yield is that all ponds above 2 mu could be used for food fish culture, with yields

113 TABLE 5 Conversion rates for pig manure and green feed for experiments in 1983 Pond size (m/mu)

Total (wet) application

Daily (wet) application

( k/mu 1

(k/mu)

Conversion rate (kg/O.5 kg fish)

(a) Pig manure 667 (1.0) 2068 (3.1) 3468 (5.2) 7333 (11.0) Average

4905 4823 4700 4700 4782

25 24 24 24 24

9.75 7.50 8.00 9.45 8.70

(b) Green feed 667 (1.0) 2068 (3.1) 3468 (5.2) 7333 (11.0) Average

13 875 13 849 13 598 13 426 13 687

70 70 68 67 68

40.5 25.5 46.0 58.5 42.5

reaching 500 kg/mu. For the l-mu ponds the farming result is less satisfactory. Large-size ponds have a less-favourable economic effect, as it is difficult to fertilize the water and to spread the feeds evenly. No apparent impact of different pond sizes has been seen on the output of different species, with the exception of silver carp; comparison of l-, 3.l-, and 4.7-mu ponds show that a 3.1-mu pond gives a 28% higher yield than does a l-mu pond, while a 4.7-mu pond yields 26% higher than a 3.1-mu pond, which tends to indicate that yield increases with pond size. Relation between pond size and D.O. Impaired respiration in fish was seen in the l-mu pond in the summer but was less pronounced in bigger ponds. From the measurements of D.O. in summer, at midnight, the lowest values of D.O. were 1.65 mg/l in the l-mu pond, 2.51 mg/l in the 3.1-mu pond, and 3.18 mg/l in the 5.7-mu pond. Organic matter The determination of organic matter was given greatest emphasis in the l-, 3.1- and 5.7-mu ponds. The result of the determination revealed that the det-

ritus component was predominant, with biomass ranging from 34 mg/l to 382.2 mg/l and comprising 81.6-85.7% of the suspended matter. Phytoplankton, with biomass ranging from 13 mg/l to 81 mg/l, comprised 9.3-14.3%. The biomass of zooplankton was the lowest, about 5-15 mg/l, occupying 4.1-4.8% of the

114 TABLE 6 Organic constituents of different-size ponds in 1982 Pond size (m’/mu)

Suspended matter

Phytoplankton

Zooplankton

Organic detritus

Total weight (mg/l)

667/ 1.0

20681 3800/ 3.1 5.7

220.7

167.6

191.2

31.5

15.6

28.3

14.3

9.3

14.8

9.1

8.1

7.4

4.1

4.8

3.9

180.2

143.9

155.6

81.6

85.9

81.4

Total weight (mg/l) Percentage in suspended matter Total weight (mg/l) Percentage in suspended matter Total weight (mg/l) Percentage in suspended matter

suspensory matters. Table 6 gives average monthly values of organic constituents. The dominant species of the phytoplankton were Cryptomonas, Scenedesmus and Euglena. Rotifera comprised the largest proportion of the zooplankton, ranging from 65.4-78.8% of the total, followed by protozoa, comprising 17-30%; the two totaled 95.5%, which was in agreement with the unsatisfactory growth of bighead. Primary productivity of fish ponds

The primary productivity is clarified by the primary production turned out from l-m3 water column through photosynthesis, expressed as grams of carbon (g C ) . The total productivity is expressed as kg C. This study determined that the production of pond photosynthesis was 175.2 mg 0,/l at the water surface (ranging 5-10 cm), 82 mg 02/1 at 20-30 cm and 17 mg 0,/l at the compensation depth. We determined the primary productivity was 2534 g 0,/m’ per year (Table

115 TABLE 7 Primary production in the experimental ponds in 1982 Unit

g 0,/m** g C/m*** kcal/m***

Month May

June

August

September

October

12.02 4.15 38.86

12.02 4.51 42.19

7.25 2.72 25.65

17.79 6.67 62.44

10.93 4.10 38.47

Average

Yearly production

12.67 4.10 38.47

2534 950 8894

*Measured. **According to Winberg (1970), calculated for 1 g 0, = 0.375 g C and 1 g C = 11.35 kcal.

7) by the light-and-dark-bottle method, i.e., daily productivity 5.28 g C/m”, comparable to the values of Hepher (1960) and Schroeder (1978). There was no increase in the primary productivity though large amounts of grass were introduced into the ponds. The silver carp, phytoplankton-feeders, and the bighead carp, zooplankton-feeders, had an average yield of 300-350 kg/mu. The total output of 1983, averaging 675 kg/mu was higher than reported by Hepher (1960) and Schroeder (1978). This was due to the number of species we selected for polyculture, the higher stocking density, and the better fish yield. Though Tang (1970) polycultured 3-7 species in Taiwan which were different from ours, the yield was only some 500 kg/mu, to date alleged to be the highest yield per unit. Our output will be higher than that if black carp and tilapia are added into the polyculture. Hepher (1960) reported the conversion rate between the yield of grass carp and common carp, and the primary productivity was only 1.5%. Noriega-Curtis (1979) reported that for silver carp, tilapia and common carp the conversion rate was 4.2-5.9%. The species which exploited primary productivity were silver carp, bighead carp, common carp, crucian carp and Wuchang fish. The use of those fish for polyculture is both rational and effective. ACKNOWLEDGEMENTS

The encouragement for this work that was given by Dr. Chen Foo Yan of the United Nations Food and Agriculture Organization and NACA is deeply appreciated. Dr. G.A.E. Gall of the Department of Animal Science, University of California, generously reviewed this manuscript and made his facilities available.

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