STUDIES ON THE EFFECTS OF FRESH AND FERMENTED PIG MANURE ON FISH PRODUCTION
Network of Aquaculture Centres
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With chemical fertilizer (N,P) as control, comparative studies were made on the effects of fresh and fermented pig manure on fish production. The results indicated that fish production in ponds supplied with fresh pig manure was the highest, compared to those with fermented pig manure, or control ponds. It appeared that fish in fresh pig-manured ponds not only could utilize bacteria, detritus and plankton, but could also directly feed on pig manure; thus pig manure was utilized better and resulted in higher fish production.
* The authors are staff members of the Asian-Pacific Regional Research and Training Centre for Integrated Fish Farming in Wuxi, China.
In China, the use of animal manure is an effective and profitable way to turn wastes into fish protein. Since little information is known on the effects of fresh and fermented pig manure on fish production, this study aims at observing and determining the effects of fresh and fermented pig manure on increased fish production.
The experiment was conducted at Dawen Fish Farm of the Centre, using six earthen ponds, each with an area of 300 sq. meters and an average water depth of 1.2 meters. The six ponds were divided into three groups: two ponds were applied with fermented pig manure (F1); two ponds with fresh pig manure (F2); and another two ponds were chosen as Control (C).
The fish species used in the experiment included silver carp (Hypothalmichthys molitrix), bighead carp (Aristichthys nobilis), crucial carp (Carassius auratus) and common carp (Cyprinus carpio).
Base manure was applied into every pond one week before the experiment started (22 June) at the rate of 150 kg/pond. Starting June, additional manure was applied once a week at the rate of 56 kg/pond each time, except for five instances when manure input was decreased to 28 kg/pond due to the overfertility of the pond water. Altogether, manure was applied into the ponds 17 times during the experriment.
Table 1. Fish species and stocking density.
Table 2. Types and input of manure in fish ponds
|Base manure||Additional manure|| Moisture|
|Total input in dry wt.|
Unit : kg
Physico-chemical parameters of pond water were measured six times every month. Water temperature ranged from 19.31.5°C and not much difference in water temperature was noted in the six experimental ponds.
The experiment was carried out for 114 days, from 30 June 1986 until 22 October 1986. During the experiment, special technical assistants were assigned to ferment pig manure and dissolve chemical fertilizer. There was no other input into the ponds except pig manure which was always weighed before application.
All the fish species were counted and weighed at the end of the experiment. The survival rate and production of wach fish species are shown in Table 3 and Figure 1. Table 4 and Figures 2–3 also illustrate the results of the parameters measured in the experiment.
Experiment results indicate that fish production in the F2 group was the highest (1529.3 kg/ha); followed by the F1 group (1059.3 kg/ha). The C group had the lowest production of 667.7 kg/ha. Generally speaking, under the same environmental conditions, fish production is mainly decided by the availability of food for fish, as well as its nutrient value. In manure-loaded ponds, natural organisms are closely related to the types and concentration of nutritive salts. It is clear that pig manure from the same source and the same rate of chemical fertilizer (N, P) were used in the experiment. The change curves on N.P. in each group after manure application are shown in Table 4 and Figure 2, which indicate that the concentration of N.P. in each pond was basically similar. But F2 group had a bigger variation, particularly at the end of experiment, In C group, N.P. concentration was more stable, but it was higher than that of the F groups. P. concentration was relatively similar (Table 4). Under the same input of manure, such difference was surely caused by various factors in fish ponds. However, fresh manure could continuously release N.P. through decomposition by microorganisms. The concentration of COD in F2 group was higher than that in F1 and even higher than in C group, which indicated that pig manure could provide more food for fish (Figure 4).
Figure 1. Fish production in experimental ponds
Table 3. Fish production in experimental ponds.
|Group/Species||Initial stocking weight||Survival rate||Gross weight||Total net weight||Daily weight||Total net prod'n|
In general, bacterial feed is formed first and then plankton grows after the application of manure. Therefore, fish with shorter food chains (such as cilver carp) always grows faster in manured ponds. In this experiment, the production of silver carp and crucian carp accounted for 67.5–69.2% of the total production from the three groups, respectively (Table 5). But there was a big difference in the absolute production of silver carp and crucian carp in the three groups (F2, 1058.3 kg/ha; F1, 715 kg/ha; and C, 454.7 kg/ha). If the production of silver carp and crucian carp was due only to the application of chemical fertilizer N.P., the excess production in the other two groups was, of course, not due to the increase of plankton (Table 4). It might be possible that fish directly feeds on the organic matter in pig manure, which provides the same rate of heterotrophic and autotrophic bacterial food organisms, But fish production in two groups of manured ponds differed. Such difference might result more from fermentation because part of the organic matter in pig manure is decomposed by bacteria during the fermentation process.
Figure 2. Change curves of N.P.
|Figure 3. Change curves of pH||Figure 4. Change curves of COD|
The growth of common carp in each group also shows the evidence mentioned above. It is known that common carp maonly feeds on benthos and organic matter covered by micro-organisms. In control ponds, very little organic matter was available for common carp. In order to get food, common carp had to dig the pond bottom in search for food; this caused high turbidity (Table 4). Therefore, the lower biomass of plankton and the lower transparency in control ponds did not result from the plankton itself. Compared with the production of other fish species, common carp production was the lowest in all experimental ponds. If the production of common carp was indirectly or directly caused by micro-organism food chains, it should have been more or less the same in both F1 and F2 groups. In fact, the production in F2 group was much higher than that in F1. According to Lindeman's “Ten Percent Law” fish could shorten their food chains for direct utilization of inputs.
Some scientists consider that fish can directly feed on and digest cow manure. Some also think that the protein of pig manure is of poor quality. Our experimental results show that pig manure is better than cow manure for fish culture, and that fish production could be increased by 30% through organic detritus. Results also indicate that bacterial biomass in cow-manured ponds is higher than that in pig-manured ponds. In the 1950s through the 1960s, one scientist who used animal manure to culture fish found that the intestines of silver carp and tilapia were full of manure and further, that these fishes grew well.
This experiment has indicated that fresh pig manure is better than fermented pig manure; and that the use of fresh pig manure can increase fish production by 144.4%. As fish can directly utilize part of the organic matter, fresh pig manure is also regarded as a good manure source for fish farming. It is therefore not necessary to ferment pig manure for fish farming.
Table 4. Water quality in different ponds.
|GROUP||NH4+ -N||PO-34 -P||Phytyplankton||Plankton||Zooplankton||Transparency (cm)|
Table 5. Percentage of fish production and growth of fish in the experimental ponds.
|% of the total||Growth order||% of fish production in each group|
The authors wish to express their thanks to the International Development Research Centre for its support of this research project. Likewise, appreciation is expressed for the interest of Dr. Brian F. Davy of IDRC and Mr. Chen Foo Yan of the Network of Aquaculture Centres in Asia, in this work.