Preliminary Studies on the Effects of three Animal Manure on the Ecological Conditions of Pond Water and Fish Growth
Hu Baotong, Wu Tingting, Feng Yingxue, Ding Jiayi and Guo Xianzhen
Regional Lead Centre in China
Asian-Pacific Regional Research and Training Centre
for Integrated Fish Farming
Changjiang Fisheries Research Institute of Fisheries Scientific Research Academy of China
NETWORK OF AQUACULTURE CENTRES IN ASIA
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Hu Baotong, Wu Tingting, Feng Yingxue, Ding Jiayi and Guo Xianzhen
Regional Lead Centre in China
Asian-Pacific Regional Research and Training Centre for Integrated Fish Farming
Changjiang Fisheries Research Institute of Fisheries Scientific Research Academy of China
The use of organic manure in aquaculture is one of the main inputs in the Chinese system of integrated fish farming. Although many scientists in China and elsewhere have done much work on the effects of animal manure on aquaculture production (Chen Qiyu et al, 1982, Buck, 1978. 1979; Schroeder 1978, 1980; McGeacin et al, 1982; Stickney, 1977; Jhingran et al, 1980; Edwards, 1980; Zweig, 1981), little is known of the series of physical, chemical and biological processes which are taking place in a pond after application of manure. The complexity of energy recycling needs further studies.
The aim of this study is to determine the independent contribution of three animal manures to changes in the ecological condition of pond water and fish production. The results to be obtained may provide the scientific basis for further research on the use of organic manure in fish culture.
The experiment was conducted at Wuxi Municipal Fish Farm in ten concrete tanks, each with dimensions of 3 × 4.6 × 1 m and a constant water depth of 0.8 m. While Tank 1 served as control, Tank 2, 3, 4 were applied with pig manure, Tank 5, 6, 7 with cow manure and Tank 8, 9, 10 with chicken manure. Tank 1, 3, 6, 10 were chosen for the pond dynamic parameters determinations. Water for the experiment was derived from Taihu Lake. Experimental period was 124 days (from June 18 to October 20, 1982). Table 1 illustrates the fish species stocked, stocking density. size and ratio. The fish species polycultured in the experiment included silver carp (Hypopthalmichthys molitrix), bighead carp (Aristichthys nobilis), common carp (Cyprinus carpio) and tilapias (Sarotherodon niloticus and S. mossambicus).
Manure sources: The chicken manure was purchased from Wuxi County Animal Husbandry Farm, but it was mixed with about 75% of wood shavings and coal cinder for bedding. The cow manure was bought from Wuxi Liyuan Cow Farm and the pig manure was obtained from the farm itself, but it was fresher than other two types of manure at the time of application.
The composition of the three types of manure, such as matter coarse protein, etc., was determined before application, which was once a week. Two weeks after stocking with fish the quantity of manure input was doubled. This was maintained till the end of experiment. On the average the daily manuring rate was 3% (in dry weight) of the total weight of the stocked fish. The frequency of measuring the various parameters related to the experiment was as follows:
Daily record was kept for weather, air and water temperature, pH, D.O. and transparency. Measurements were taken at 6:00, 13:00 and 17:00 hours. D.O. was monitored by YSI - 57 oxygen meter.
The following parameters were determined once every two weeks:
total weight of suspended matters (seston).
The parameters of pond dynamics were monitored everyday during two separate weeks (July 16–22, October 8–14).
Fish growth and yield were assessed with of without organs at the end of the experiment. The coarse protein content of each species was also measured.
1. Physico-chemical Parameters of Tank Water
Water temperature during the experiment ranged from 17.5–32.5°C In general, water temperature was the highest at 13:00 and the lowest at 6:00. But the water temperature reached its highest point at 17:00 in July and August. During the whole experimental period, water temperature was the highest in August compared with that of other months. Therefore, water temperature had visible seasonal and diurnal changes. The difference of water temperature of 10 experimental tanks was 0.5°C.
Transperency and colour of tank water
The table below illustrates the transparency and colour of tank water treated with different manure.
|Water colour||light green||yellowish brown||brown||grass green|
Do variations during the experiment as shown in Figure 1 were different in the control and experimental tanks of each type of animal manures.
pH and total alkalinity
The following Table and Figure 2 and 3, illustrate the changes of pH and total alkalinity.
|Control Tank||Pigmanured Tank||Cowmanured Tank||Chickenmanured Tank|
PO4 and Inorganic N
At the early experimental stage, i.e., one month after the starting of the experiment, the PO4 concentration was similar in three different animal manured tanks, ranging from 0.005-0.02 ppm. After July 22, PO4 concentration was greatly increased (Fig. 4), reflecting on the fertility of these three animal manures.
NH4-N, No3-N, were determined, and their variations in different type of manured tanks are shown in Figure 5, 6, 7.
BOD and COD
|BOD (g O2/m2day)||2.84||5.48||3.66||6.27|
|COD (mg O2/l)||14.60||14.01||13.70||14.51|
Note: These data were obtained on 18 August 1982.
2. Biological Parameters
Organic detritus and bacteria
The suspended matters contained the highest proportion of organic detritus in weight. The organic matters in the cow-manured tank accounted for 82.1% of total weight of suspended matters, chicken and manured tanks were 77.9% and 77.6% respectively (Table 2).
The dominant species of planktonic bacteria were Bacillus, Saphylococcus, Brevibacterium, The molds consisted of Aspergillus and Penicillus while the actinomyces covered Streptomyces and etc.
The total numbers of heterotrophic bacteria of the planktonic group in the pig-manured tank were 38.9 × 102/ml, chicken and cow-manured tanks were 30.8 × 102/ml and 24.4 x 102/ml respectively. The variation of bacteria biomass is shown in Figure 8.
In the experiment, phytoplankton grown in the tanks consisted of 10 genera of cyanophyta, 14 genera of chlorophyta; 8 genera of Bacillariophyta, 3 genera of Euglenophyta; 1 genus of Cryptophyceae and 1 genus of Pyrrophyta. However, the dominant species varied in accordance with the seasons. In early July, the dominant species in the control tank were Coelastrum, Merismopedia. From August to October, Microcystis was dominant except in September when Oscillatoria was more dominant in number. In pig-manured tank, Scenedesmus was dominant in early July and again in early October while Microcystis was the dominant group in mid October. In chicken-manured tank, Merismopedia and Synedra were the dominant species in mid August and Spirulina became dominant in late August. But Cryptomonas and Euglena appeared to be the dominant species in September and October. In the cow-manured tank, however, no visible dominant species of algae was found.
The biomass of phyto-plankton varied with the different types of animal manure. The biomass of phytoplankton in the chicken-manured tank was 58.1 mg/l, pig-manured tank 41.9 mg/l and cow-manured tank 35.3 mg/l, while in the control tank the biomass was only 24.1 mg/l. The changes of phytoplankton during the experiment are illustrated in Figure 9 (a).
The varieties of zooplankton in Tank 1, 3, 6 and 10 were basically the same. Rotifera covered 19 species of 14 genera of 7 families of 3 sub-orders. The dominant species in the experiment were Trichocerca and Proales; cladoceran contained 5 species of 4 genera of 3 families. The dominant ones were Moina and Diaphanosoma. But cyclops was the major species of copepoda.
The biomass and percentage of the main varieties of zooplankton are listed in Table 3. Comparatively speaking, the biomass of rotifera was the highest, which accounted for 82.5% of the total biomass of zooplankton in the chicken-manured tank, 69.2% in the pig-manured tank and 64.7% in the cow-manured tank.
Results of continuous determination in one week
Total N, planktonic bacteria, the biomass of phytoplankton and zooplankton in the experimental tanks were continuously monitored in two separate weeks after the input of animal manure. The first monitoring period was performed in July 16–22 and the second in October 8–14. The biomass of phytoplankton declined after the first manuring due to rain. The phytoplankton biomass in Tank 1 decreased from 48.2 mg/l to 27.2 mg/l, Tank 3 from 22.04 mg/l to 19.48 mg/l, Tank 10 from 24.96 mg/l to 13.36 mg/l and it was the same case in Tank 6.
However, the tatal N, biomass of phytoplankton and zooplankton gradually increased after the 2nd input of manure, as shown in Figure 10.
3. Effects of three Animal Manure on Fish Production
The effects of chicken, pig and cow manure on the fish production are clearly illustrated in Figure 11.
Fish survival rates in manured tanks were higher than that in the control tank. The survival rate in the chicken-manured tank was 98%, which was the highest, while the survival rate in the pig and cow-manured tanks was 90.7% and 87.3% respectively.
Growth rate of fish stocked in the three different animal manured tanks are shown in Figure 12.
The individual body weight increment of tilapia in the chicken-manured tank was comparatively higher than in the cow and pig-manured tanks. In addition to that, chicken manure was more preferable for the growth of common carp while pig manure was more beneficial to the growth of silver carp and bighead carp.
The experiment showed that the fish output of silver carp, bighead carp, common carp and tilapia with the method of polyculture could be increased by the utilization of pig, cow and chicken manure. The fish output in pig, chicken and cow manured tanks was 275.4 jin*, 265.7 jin and 203.4 jin respectively. Breeding of tilapia occurred in Tank 1, 3 and 10 from which 0.3 jin of tilapia (3–6 cm) were harvested from Tank 1, 1.73 jin from Tank 3 and 0.79 jin from Tank 10.
* 1 jin = 500 g
Manure conversion rate and protein efficiency
The conversion rate of pig, cow and chicken manure was 3.5, 6.4 and 7.4 respectively (in dry weight).
The protein efficiency and utilization rate of each animal manure were as follows: pig manure 2.91 and 29.46%, cow manure 1.69 and 17.85%, chicken manure 1.44 and 14.36%.
As mentioned above, different fish output and food conversion rate were obtained with different animal manure. Based on the different prices of pig manure **(¥0.005/jin), cow manure (¥0.005/jin) and chicken manure (¥0.020/jin), the respective production cost of 1 jin marketable fish was calculated as ¥0.118, ¥0.207 and ¥0.210.
** ¥ 1 = US$0.50
1. Some Changes in Pond Dynamics
The changes in pond dynamics would occur usually after the manure application. Changes in transparency ranged from 20–45 cm with the control tank being at 45 cm. The maximum transparency in the treated tanks was about 40 cm. The changes in water colour resulted mainly from the different composition of phytoplankton.
Based on the data obtained, the transparency appeared to be closely related to the quantity of suspended matters. Therefore, the following experimental equation can be worked out:
|F =||biomass of zooplankton (mg/l)|
|T =||maximum transparency|
The maximum transparency of three animal manured tanks was 39.3–40 cm. and that means To = 40 cm. Hence, the biomass of zooplankton can be calculated after measuring the transparency (T) of pond water.
The chemical composition of these three animal manure were listed in Table 4. Pig, cow and chicken manure contained 2.45%, 2.16% and 10.43% of protein respectively. As each type of animal manure had different nutrient compositions, the changes in pond dynamics were observed after manure application.
The concentration of PO4 was significantly raised after manure application. In mid July, PO4 in the pig-manured tank increased by 42.8 times, cow-manured tank by 7.7 times and chicken-manured tank by 4.3 times. At the same time, NH+4-N, NO-2-N and NO-3-N also increased (Figure 6, 7). These provided favourable conditions for phytoplankton growth. In comparison with the control tank, the biomass of phytoplankton in the chicken-manured tank increased by 141%, pig-manured tank by 73.9% and cow-manured tank by 46.5%.
The quantity of organic detritus was enhanced accordingly. In the chicken-manured tank, the quantity of organic detritus increased by 58.7%, cow-manured tank by 28.8% and pig-manured tank by 21.9% compared with that of the control tank. The biomass of heterotrophic bacteria in pig, chicken and cow manured tanks were multiplied by 2.13, 1.68 and 1.34 times respectively. Organic detritus and bacteria not only promoted the growth of zooplankton, but also provided the food sources for filtering and omnivorous species of fishes (Hu, 1981; Schroeder, 1978 and 1980).
After the loading of these three animal manure, the biomass of zooplankton was raised. Compared with the zooplankton biomass in the control tank, it was increased by 68.0% in the chicken-manured tank, 29.7% in the pig-manured tank and 29.5% in the cow-manured tank. Therefore, the survival rate of fish in the pig, chicken and cow manured tanks were enhanced by 8.0%, 16.7% and 3.93% in comparison with that in the control tank. Similarly, the fish yield was increased by 5.2, 5.1 and 3.9 times respectively.
The fish production was proportional to the quantity of suspended matters. In the control tank, natural water from Taihu Lake was the only nutritive source for the growth of planktonic food organisms. The quantity of suspended matters was only 167.8 mg/l and consequently the fish yield was the lowest. The amount of suspended matters in the chicken-manured was mixed with certain amount of wood shavings and other substances, which showed that chicken manure was not the best food base for fish farming although the quantity of organic detritus was relatively higher. As a result, chicken manure was not considered as the best one in this experiment. Besides, chicken manure is alkaline with a pH value of 9.0. Due to the high pH value, it is easier for the formation of NH3, which is harmful to the growth of fish at high concentration (Merkel, 1981). The quantity of suspended matters in the pig-manured tank was higher than that in the control tank, hence fish output was 35.7% higher than that in the control tank. However, the relations between the quantity of suspended matters and fish production are relatively complicated and need further research and studies.
In comparison with the feeding habits of silver carp, bighead and common carps, the feeding range of tilapia is even wider. Hence its daily body weight increment was the highest. The digestive rate of algae by tilapia was higher than that of silver carp (Liu Lin, 1979). As the biomass of phytoplankton in the chicken-manured tank was 141% higher than that of control tank, it is clear that chicken manure provided more effective food base for the fish growth than pig and cow manures. Perhaps this may be the main reason why tilapia grew best in the chicken-manured tank. In the pig and cow manured tanks, the quantity of organic detritus was not markedly different, so the individual body weight increment of tilapias in these two tanks were similar.
2. Effects of animal manure on fish growth
The experimental results showed that pig, cow and chicken manure loaded in the fish pond can directly or indirectly serve as nutritive sources for growth of silver carp, bighead carp, common carp and tilapia. The effect of manure on the fish growth is not only determined by its chemical composition but also by its freshness (Merkel, 1981). Therefore, different animal manure have different effects on the growth of different fish species (Figure 12).
When the manure were applied to the tanks, the suspended and dissolved organic matters increased thereby raising the levels of BOD and COD. The fertility of pig manure was the richest and the concentration of COD and BOD were also the highest in the pig-manured tanks. According to the data obtained on 18 August 1982, COD concentration in the pig-manured tank was 14.01 mg/l and 13.70 mg/l in the cow-manured tank. Figure 13 indicates that BOD concentration was also high because of the comparatively larger amount of plankton and bacteria. This factor, particularly visible in the pig-manured tank, affected the dissolved oxygen content. In general, DO of the experimental tanks reached the lowest point at 6:00, with the minimum level of DO in the pig-manured tank at 1.9 mg/l, cow-manured tank at 2.5 mg/l and the chicken-manured tank at 2.8 mg/l. Hence the contradition between the manure fertility and the dissolved oxygen arose.
Through comprehensive analyses on the effects of these three animal manure on fish growth, it was found that the pig manure was relatively better than the chicken and cow manure. But the dissolved oxygen level appeared to be minimum in the pig-manured tank. As Figure 13 illustrated, the primary productivity and BOD were high, which indicated that the richer nutrient base through manuring would result in the decrease of the DO level which in turn would affect the growth and survival rates of fish. Therefore, the quantity of manure to be applied and the method of application have to be standardised through further studies.
3. Changes in Pond Dynamics observed through Continuous Monitoring
After manuring, continuous measurements were conducted twice, in July 16–22 and October 8–14, 1982, and the parameters measured included total N, the biomass of planktonic bacteria, phytoplankton and zooplankton. As a result of much rain during the first measuring period, all the parameters exhibited a narrow range of change. The phytoplankton biomass in Tank 3 and 6 declined and the manure had no fertilizing effect. So it is advisable not to apply manure into fish ponds during the rainy days. At the second measuring period, all the parameters exhibited correlative changes but the range was comparatively different. The total N concentration was the highest on the 2nd day of manuring but started to decrease and stabilize after that. The biomass of plankton bacteria and phytoplankton reached the high peak on the 3rd day while the zooplankton biomass attained the maximum on the 4th day. Except for the chicken-manured tank of the biomass of phytoplankton in the other treatments began to decline and gradually stabilised. This could indicate that the chicken manure could have a longer fertilizing effect than pig and cow manure. Based on the changes observed the optimum manuring frequency may be once every 4 days at water temperature of 19.6–24.6°C.
According to the data obtained at the 2nd continuous measurement, the total N increased to 4.90 mg/l in pig-manured tank (Tank 3), 4.06 mg/l in cow-manured tank (Tank 6) and 5.04 mg/l in chicken-manured tank (Tank 10). Chen Qiyu et al (1982) reported that the reproduction of phytoplankton and zooplankton attained maximum level when the total N increased to 6–8 mg/l. Through analysis of total N, it was apparent that the primary productivity in the tanks treated with three different types of animal manured was below the maximum point because of high pH value, which was probably caused by the newly prepared cement tank. As a result, more NH3 was lost and all the N in the tank water was not fully utilized. In the control tank which received no manure, the N concentration was 4.62 mg/l. It may be concluded that the primary productivity was restrained because of low P concentration and high N/P value.
We wish to express our thanks to Liu Meizhen, Yang Yejing, Chang Laifa, Zhu Yun, Yang Yaping, Huang Jikuen, Yu Yongshen, Liu Zhiyun, Wan Junhua and Chou Enhua for their participation, Mr. Zweig, resident advisor of FAO at the Wuxi Lead Centre, for his share in the experimental design and his valuable instructions and Mr. Shan Jian, Deputy Director of Changjiang River Fisheries Research Institute, for his proof-reading of this paper.
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