NACA/WP/86/32

November 1986

Comparative Study on the Effects of
Fresh and Fermented Pig Manure on Fish Yield

Freshwater Fisheries Research Centre
Chinese Academy of Fisheries Science

NETWORK OF AQUACULTURE CENTRES IN ASIA
Bangkok, Thailand

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COMPARATIVE STUDY ON THE EFFECTS OF FRESH AND FERMENTED PIG MANURE ON FISH YIELD

Han Yugin
Jiangsu Biogas Research Institute
Ding Jie-yi
Fresh Water Fisheries Research Center
Chinese Academy of Fisheries Science

Animal manures have been an important organic manure source of fresh water aquaculture in China as well as the principal material of biogas fermentation in rural areas. This experiment aimed at raising the economic efficiency of the techniques of biogas fermentation, opening a new way to utilize fermented manures comprehensively and promoting the synchroneous development of fresh water aquaculture and biogas utilization.

INTRODUCTION

This experiment has been conducted in two adjacent fish ponds, which were newly dug out in Loyan Perigree Livestock Farm, Wujin Country. Two treatments were designed, that is, Pond No. 1 applied with fermented pig manure and Pond No. 2 applied with fresh pig manure. The area of Pond No. 2 was 0.817 mu, while that of Pond No. 1 was 0.675 mu in 1983, 0.817 mu in 1984. Water depths were the same, that is 1.5 m. The two fish ponds were fertilized with fresh and fermented pig manures respectively. The fermented manure came from pig excreta fermented in a hydraulic biogas tank with a capacity of 10 m³, whereas fresh pig manure came from the excreta of pigs which ate the same ration in the same pigsty as the former.

The stocking density of fingerlings and the measures of rearing management are the same by and large. In 1983, plankton-feeders occupied 50%. The fingerlings were actually reared for 238 days from stocking on the 22nd of March to harvesting on the 6th of Nov. They were stocked and captured at one time. In 1984, plankton-feeders occupied 56%. The fingerlings were actually reared for 242 days from stocking on the 2nd of Mar. to harvesting on the 1st of No. On the 25th of July, the summer harvest of Silver carp was conducted and summer fingerlings were restocked for the second time.

In order to guide the fertilization, some measurements about the nutrients of manure and the chemical properties of pond water have been taken by routine sampling apart from daily measurements of transparency, temperature and D.O.C. of pond water.

Table 1. Analysis of the Constituents of Different Manures


Year	Type	Total solid %	Total N %	organic C %	pH	NH₄-N%	Total P mg/L	Total K %
	Biogas ferment liquid	0.6814	0.0714	0.10	7.38	0.0538	23.5	0.0968
	fresh pig feces & urine	1.6297	0.0922	0.36	7.35	0.0586	31.6	0.1203
	biogas ferment dregs	10.7	0.27	3.10			0.187%
1984	biogas ferment liquid	0.4884	0.1092	0.12	7.43	0.0998	125
1984	pig feces flush	0.7551	0.0331	0.09	7.20	0.0269	106
1984	pig feces	21.3	0.32	1.33			0.587%

The amount of fertilization depends upon the transparency of pond water and its chemical properties, not on the ration. (See Table 2)

Table 2. The Amount of Fertilization


Year	treatment	base manure	additive manure	Transparency	temperature
1983	Pond No.1 0.675 mu		35300 kg	15–50 cm	12.2–37°C
1983	Pond No.2 0.817 mu		16700 kg	15–45 cm	12.5–38°C
1984	Pond No.1 0.817 mu	1000 kg	9950 kg	15–35 cm	11.0–38°C
1984	Pond No.2 0.817 mu	500 kg	7150 kg	15–40 cm	11.0–38°C

In 1983, the total amount of solid pig feces put in the biogas tank was 558 kg, producing 122,2 m³ of gas. The rate of gas generating is 0.219 m³/kg TS. In 1984, the total amount of solid pig faeces put in the biogas tank was 188 kg, producing 52.4 m³ of biogas. The rate of gas generating is 0.279 m³/kg TS with a methane content of 64.8%.

RESULTS

1) Increasing the fish output

The fish output in 2-year-experiment is listed in Table 3. As a wjole no matter whatever it is, plankton-feeders or feed-eaters, pig manure after fermentation shows conspicuously better effects on fish yield.

In 1983, the net fish output per mu of Pond No.l was 451.7 kg with an increase of 25.6% above the output of Pond No. 2. Among the output, plankton feeders increased 5.1%; fee-eaters increased 44.7%.

In 1984, the net fish output per mu of Pond No. 1 was 474 kg with an increase of 7.1% above that of Pond No. 2. Among the output, planktoneaters increased 4.7% while feed-eaters increased 9.2%. The increase of feed-feeders are often greater than that of plankton-feeders.

2) Improving fish quality (see Table 4)

The results of comparative analysis on the nutrients of fish body show that the quality of various species has been improved to some extent by using fermented manure in fish culture. In 1983, the results of the analysis indicated that the content of proteins in fish body increased, while the content of fats decreased relevantly. In 1984, both nutritional elements in fish body increased. For plankton-feeders, the proteins in fish body increased by above 0.5%. Amino acids are principal constituent elements of proteins, therefore, the content of amino acid and its composition are marks of the quality of proteins.

We analysed 17 amino acids in fish body of Silver carp Hypophthalmichthys molitrix and Chinese bream Megalobrama amblycephala. We found that the total content of amino acids of Silver carp in Pond No. 1 was 12.8% higher than that in Pond No.2. The total content of 9 human essential amino acids in fish body of Silver carp in Pond No. 1 was 9% higher than that in Pond No. 2. The increase of Lysine is conspicuous, up to 11.6%. The total content of amino acids in fish body of Chinese bream in Pond No. 2 was 2.5% higher than that in Pond No. 2. The total amount of 9 essential amino acids in fish body of Chinese bream in Pond No. 1 was 2.9% higher than that in Pond No. 2, therefore, applying fermented manure in fish culture not only increases the protein content in fish body, but also raises the nutritional value of the proteins. Fermented manure obviously improves the quality of plankton-feeders.

3) Increasing income

From the assessment of income and expenditure, the economic benefit is apparent. In 1983, the net income per mu of water surface of Pond No. 1 in creased 127.27 yuan, 34.23% higher than that of Pond No. 2. In 1984, the net income per mu of water surface of Pond No.1 increased 72.91 yuan, 11.7% higher than that of Pond No.2. The average increase of two years is 100.09 yuan.

DISCUSSION ON THE CAUSE OF INCREMENT

1) Promoting the proliferation of plankton

Plankton-feeders feed mainly on plankton, therefore, the output of plankton-eaters is directly related to the quantity of plankton, which are dependent upon the nutritional salts in water body. The content of the effective constituents is so high in fermented manure that its application can increase the content of nutritional salts in the water. For example, ammoniacal nitrogen in biogas fermentation liquid occupies 75 in total nitrogen, whereas that in fresh pig manure only holds 63.81%. The obvious increase of inorganic nitrogen in the water promotes the proliferation of plankton, (see Table 7).

There is no difference between species of plankton in two fish ponds. But both biomass of plankton and gross wiight of phytoplankton are greater in Pond No. 1 than those in Pond No.2. (see Table 8 & 9)

The seasonal change of phytoplankton indicates that the predominant species Cryptomonas, which are easy for fish to digest, are much more in Pond No. 1 than that in Pond No. 2 during Apr--Jun period, with secondary species green algae and euglenoid; during July--Sept. period, the predominant species green algae, which are undigestable for fish, keep higher in Pond No. 2. It indicates that pig manure after fermentation is beneficial to the proliferation of digestable phytoplankton, and thus, the composition of phytoplankton has been improved. (see Fig 1--6)

2) Improving D.O.C. in water body

Organic materials applied into fish ponds as manure need a process of decomposition before their nutrients can be absorbed and utilized by phytoplankton. The decomposition of organic material must consume certain amount of oxygen, nevertheless, the D.O. in the water is the necessity of the development of fish. Applying huge amount of fresh organic manure often causes fish pond to lack oxygen and then, the growth of fish would be retarded. Therefore, the preparation of organic manure, suchas compost by heaping or scaking, is an important technique of fertilization in fish ponds. On one hand, biogas fermentation techniques can utilize part of energy released during fermentation; on the other hand, it can enable organic materials to decompose fully, and then, the loss of the nutritional elements will decrease while the use of the organic materials may be safer. We found that the average D.O.C. in Pond No. 1 was 43.5% higher than that in Pond No.2. During the period of 23 days, the lowest D.O.C. in Pond No.2. was 0.7 mg/l, with 14 days below 2.0 mg/l; whereas the lowest D.O.C. in Pond No. 1 was 1.1 mg/l, with only 6 days below 2.0 mg/l. During the experiment period, the fish in Pond No. 1 gasped for air 16 times with the use of aerator for 4 hours; while the fish in Pond No.2, 22 times with the use of aerator for 6.5 hours, besides, with fresh water added twice. (see Fig. 7). This indicates that biogas fermentation liquid greatly improves the chemical properties of water body and can promote the growth of So it is an important factor to raise fish yield.

3) Raising the rate of food utilization

Fish feeds are the material basis of the growth of various species of feed eaters. Under normal conditions, the output of feed-eaters has correlation with the amount of feed. From the statistics of feeding, there was no great difference between the amounts of feeding of two ponds in 1983 and they were all the same in 1984. (see Table 10). The application of fermented manure could reduce the consumption of D.O.C. in pond water and increase the amount of oxygen produced by phytoplankton; therefore, the ecological environment for fish would be improved. The growth of fish could speed up, and the food utilization would be higher. In 1987, the food co-efficient of Pond No.1 was 3.6 while that of Pond No.2 was 4.51; in 1984, food coefficient of Pond No.1 was 4.85 while that of Pond No.2 was 5.29. It can save 0.22--0.45 kg of feeds by using fermented manure to produce 0.5 kg of feed-eaters, so that we can reduce the cost and increase the economic benefit.

After harvest, we analysed the pond humus. (see Table 11). The results indicated that the pond humus in Pond No.2 was thicker, with rich content of nutrients. This shows the lower food and manure utilization rate of Pond No.2.

4) Widening the eay of utilizing biological energy

The statistics on the utilization of main constituents of input in fish ponds suggest that so far as nitrogen was concerned, fermented manure suffered some loss of nitrogen, about 5% during the process of fermentation. Since the content of quick effective nitrogen was much higher in fermented manure, ammonia suffered more loss after being put into fish ponds, therefore, the recovery rate of nitrogen in Pond No.1 was only equal to one third of that in Pond No.2 in the light of plankton-feeders; on the other hand, the application of fermented manure improved the chemical properties of pond water such as D.O. and then raised the utilization rate of nitrogen as for feed-eaters although the total recovery rate of nitrogen decreased by 7.5%

Biogas fermentation makes the organic materials of pig manure to decompose fully, while the total solid decreased partly. Carbon is converted to the gas with biogas as its major part. One part of carbon sinks to the bottom of the biogas tank and a considerable part is in suspension in biogas fermentation liquid, which can be utilized by fish. Statistics suggest that fermented material is more effective to plankton-feeders. At the same time, the utilization by feed-eaters is also enhanced.

In general, the application of fermented manure in fish ponds greatly increases the value of utilization of energy from the biological resources creating a new way of comprehensive utilization of energy from biological resources

SUMMARY

1) Pig excreta after biogas fermentation are used as a manure source in fish ponds. Not only partial energy can be obtained, but also the decomposition of pig excreta can be conducted fully in anaerabic conditions, and the quick effective nutritional constituents would be raised and preserved. As a result, the biological resources can be reasonably utilized.

2) After applying fermented manure in fish ponds, the content of effective nutritional constituents augmented, resulting in the proliferation and growth of plankton and the improvement of the composition of phytoplankton. Fermented manure decreased the D.O. consumption during the process of decomposition of organic matter, and thus, it improved the ecological environment for various species of fish; it raised the food utilization rate with the result that fish yield could be increased.

3) Based on the comparative study for 2 years, the fish yield by using fermented manure was 7.1–25.6% higher than that by using fresh pig manure. The increment of feed-eaters is greater than the increment of plankton-feeders. At the same time, the quality of fish has been improved. It's worth extending the techniques owing to apparent economic benefit.

4) The synchroneous development of livestock-poultry culture, biogas utilization and fresh water aquaculture should be positively encouraged. It could lead to multi-storied comprehensive utilization of biological resources so as to raise the value of biological resources.