5.1 Collection and analysis of existing data
5.2 Tanks and yard-scale experiments
5.3 Studies of animal manures
5.4 Studies of green manure
5.6 Straw and other high-fibre substrates
5.7 Fish stock and stocking rates
5.8 Silt and pond bottom studies
5.9 Experimental studies and economic evaluations
The approaches that could be adopted for investigating the problems that were described earlier, are discussed below. In suggesting approaches, the task force took into account the facilities available in Wuxi, the manpower allotted and the time frame of UNDP/FAO assistance to the Centre.
It is understood that several communes in China have detailed records of farming and production. These data can provide a valuable base for planning specific details of the Lead Centre's experiments and for evaluating the results of experimental work as extrapolated to commercial production. Efforts should be made to collect and review these records, and if the nature of the data warrant it, appropriate analysis should be undertaken to derive preliminary indications of relationships and production rates. Commune records Should be examined for information of the following types:
- Stocking ratios and densities
- Organic inputs
- Fish yields
- Yields in relation to pond depth and area
- Yields in relation to supplemental feeding
- Economic value or productivity, and labour for crop, animal or fish farming
- Occurrence and effects of fish disease
- Mortality rates of fishes
- Pond management (aeration, water replacement, etc.)
- Silt removal, and its use and value
It will also be useful to collect similar information from other locations within and outside of China so that yields at Wuxi may be compared with methods and climatic conditions existing elsewhere. The computer facilities to be installed at the Wuxi Lead Centre should prove a valuable tool in this data analysis. Meteorological data, e.g., the ratio of cloudy to sunny days, may have major impact on pond ecology, water quality, and fish yields. Such data, if not available at the commune or fish farm level, may be attainable from local governmental meteorological stations.
An analysis of available information may provide guidelines for experimental designs, as well as permitting essential economic evaluations.
It is seldom possible to have sufficient ponds to meet the needs of individual investigators in a research centre to enable each to work independently. Because of this and more importantly the interaction and interdependence of factors in culture systems, it is important that investigations are carried out by multidisciplinary teams, whenever necessary. This will require careful consideration of the variables involved and how each experimental system can be used to provide a variety of types of information. Certain types of data such as related to water quality, incidence of disease and pathogens, and pond dynamics, can be gathered concurrently with most of the experiments for evaluating the types and rates of waste application.
Certain types of preliminary studies can be conducted in small tanks or pools, either indoor, or outdoor. An example of such an application would be the evaluation of treated or hydrolysed straw against untreated straw (see page 16) where the test animal might be a tilapia, a prawn or both. Such a preliminary evaluation could be made in indoor tanks. Comparative studies of green manure and animal manure, or of pig manure and chicken manure, might also be conducted in small tanks or pools. In this case the tests should be made outdoors because sunlight would be an important part of the equation. When applicable, the use of pools or tanks can provide savings in time and money because pools and tanks are less expensive, and require less space than ponds, and can indicate what additional testing in ponds is needed. The use of pools can also: (1) permit a greater replication of trials, which can increase the reliability of the results; (2) provide a greater uniformity among experimental systems; and (3) be more easily and reliably sampled than larger ponds. It must be recognized, however, that the use of such systems has disadvantages which limit their use. For example, they represent an artificial environment which may alter the growth rates and feeding activities of the species stocked. However, it has been reported by several researchers that tilapia, small carps, or prawns, in limited numbers, can achieve sufficient growth in outdoor pools of 3 or 4 m diameter to permit a reliable interpretation of experimental treatments.
Obviously, the inputs of manures and/or substrate, and the numbers of fish stocked in such systems are to be carefully standardized and calibrated. For example, in order to ensure growth capability, the numbers of small tilapia stocked in a 4-m diameter pool receiving supplemental food should not exceed about 30 individuals, although either the number stocked, or the growth potential, could be increased by use of a small aerator. Every input must be carefully standardized. All experimental animals (fish or prawns) should be of the same initial size and condition, and the input of manure or substrate should be uniform to all tanks. It is suggested that soil and silt layers on pool bottoms should have a uniform thickness of at least 3 cm. Successful experiments have been conducted in such pools constructed of fibreglass, or having a relatively thin, inert plastic liner. It should be emphasized that the principal value of such testing is to determine whether the procedures under examination exhibit sufficient promise to warrant additional evaluation in ponds.
Manure compositions vary over such a wide range that some pre-selection of the types should be done prior to pond experiments.
Manures from pigs, cows, ducks and chickens receiving high, medium, and low quality feeds should be analysed for nitrogen, phosphorous, potassium, true protein, total fibre, lignin and pepsin digestible energy (pepsin and lignin give about the same results). A high quality chicken feed contains approximately 3 000 calories available energy/gram, 20 percent protein, 10 to 15 percent fish meal or soybean meal plus sulphur-bearing amino acid supplement, and less than 10 percent ash. Lower quality feeds contain less energy, less protein, and more ash and fibre.
The composition of the various manures will indicate the range of inputs that can be expected in fish ponds in an integrated farm. Since it will not be practical to pond test all manure compositions for fish growth, yard-scale experiments in outdoor tanks should be conducted. Although fish growth rates in tanks are usually quite different from growth rates observed in ponds, relative growth rates of fish in the several tank tests will indicate which of the manures should be investigated in pond trials.
Methods for the calibrating, handling and distribution of manures to be used in ponds must also be carefully developed. While the additions will be calibrated on a dry weight basis, they will have to be placed in the ponds, or in the fermenter or composter, when fresh, and the amounts must be carefully monitored. In some cases it may prove desirable to hold the pigs, or other experimental animals, in such a position that their total manure falls or flows directly and continuously into the pond. In this case it would be necessary to take frequent weights of the animals so that manure production could be calculated on the basis of their weight. Such a procedure should be acceptable for experiments in ponds over a growing season, but occasional adjustments may be necessary to equalize the weights of animals providing manure to the different ponds.
In the case of smaller experimental units, such as tanks or pools, it probably will be necessary to take direct weight of each lot of added manure. In this case it will be necessary to standardize the procedures so that the material weighed has a consistent and uniform degree of freshness and moisture content. This, of course, would apply to both green and animal manures.
In the Chinese system of integrated fish farming, green fodder is added primarily to feed the herbivorous fishes, and secondarily to provide manure in the form of faeces from grass carp and/or other herbivorous fishes. Green fodder may also have a significant value as a manure when not eaten by grass carp, or other herbivores. It therefore follows that green fodder should be evaluated: (1) as a combination of feed and manure; and (2) purely as a manure. Such information could have special value in other areas that might have an abundance of green fodder, but little or no animal manure for use in fish ponds. It would also improve our understanding of the relative benefits derived from green and animal manure in Chinese fish ponds. However, in order to make such separate evaluations it would appear necessary to conduct experiments both with and without grass carp. Green manure should therefore be evaluated in terms of: (1) its value as purely a manure when compared to animal manure; (2) its use as direct food; and (3) its manurial value for the production of natural foods (bacteria, plankton, benthos, etc.).
(i) Green fodder as a manure
These studies would compare the benefits of green manure and animal manure in terms of fish yield, water quality, and rates of production of natural food. The experiments will be carried out with standard polycultures of silver carp, bighead carp, common carp and tilapia, but without grass carp. These studies should also compare the relative values of: (1) different types of commonly used green fodders (coarse grasses, fine grasses, vegetable tops, etc.); and (2) their relative values when given as fresh fodder, or when applied after composting.
(ii) Green fodder as food and manure
These experiments would duplicate those outlined in the previous section (same input of green on composted fodder, same densities of fishes) except that the polyculture would contain sufficient grass carp to utilize a significant portion of the fodder as direct food.
5.5 Pond Dynamics
The path from manure input to fish growth is sufficiently complex that it warrants study in the more simplified environment of a tank prior to investigations in ponds. It appears that what must be identified are the rates at which components of the manure are either directly harvested by the fish or converted into substances that form food of fish and then the rates at which these substances are harvested and utilized for fish growth.
Analyses of cow and chicken manure reveal low available energy (500 to 1 200 cal/gram), low true protein (1-10%), high ash (about 20%), and high fibre (about 50%) as compared to some fish feeds (3 000 cal/gram; less than 10% ash). This implies that while fish may graze on manure as it is supplied to the pond, some cycling of the crude manure components occurs to change them into a more useful food.
Naturally or artificially labelled (e.g., using carbon-14) straw or cotton fibre plus appropriate chemicals (also labelled) and polysaccharides will be used to make a simulated manure. This manure will be used as the input for a tank study. To simplify the initial tests, the tank will not have a bottom silt layer and will not be stocked with fish. Rates of fibre disappearance (digestion) and chemical uptakes (by autotrophs and by heterotrophs) will be monitored. Concurrently, rates of autotrophic production (by chlorophyll-A; primary production; algae accumulation on walls and bottom) and heterotrophic production (epifluorescence) on detritus and on tank wall slime; accumulation of mucopolysaccharides on solid surfaces will be estimated (exact rates will not be possible to determine due to the complexity of the system). In addition, total BOD of the tank will be monitored by covering the tank, stopping aeration if in operation, and measuring the rate of decrease in tank DO. This provides an indication of total respiration of all organisms in the tank. Respiration is a qualitative indicator of metabolic processes.
Incorporation of the substances derived from the fibre and chemicals of the manure into algae and other microbial cells will be monitored by following the labels through the food web. As understanding of the paths is gained, tests in fish-stocked tanks will be conducted. The incorporation of the labels into the fish bodies should permit evaluation of paths and rates leading from manure to fish and hence a more efficient use of pond and manure.
The use of aerators would undoubtedly affect the ability of ponds to utilize manures and other wastes. Selected types of aerators should be used and their effects on pond dynamics monitored.
Digestibility of substrates with a large percentage of fibre is low, but proper treatment can increase this digestibility. This treatment often incorporates crushing the fibre and some hydrolysis. Reported results indicate that chopping or crushing prior to hydrolysis is preferable.
Using a ball mill or equivalent, the straw should be crushed and broken to pieces 0.25-1 cm long. The fragments may then be moistened with 1 percent NaOH for one or more days at ambient temperature and at 25°C for a standard control. The action of the NaOH is to swell the fibre and partly separate the lignin from the cellulose.
Digestibility of treated and non-treated straw can be measured by using pepsin or trypsin enzymes (although fish may have trypsin enzyme, pepsin has been reported to give similar results) to solubilize that part of the straw which is digestible. A standard temperature, e.g., 25 or 30°C, can be selected, and with proper pH adjustment, the enzyme added to the treated and non-treated straw or other fibre in an Ehrlenmeyer flask and shaken (on a shaker table or by hand a few times a day) for a selected length of time (one to several days). Dry weight loss of the solids from before to after digestion is an indication of digestibility. It will be useful to measure lignin, cellulose, and total fibre in the original straw and in the treated straw, before and after digestion.
Fish growth rates on these high-fibre substrates can be measured in tanks. Since about half the dry weight of the fibre is carbon, and the original fibre contains low amounts of N and P, the C:N:P of the substrate should be adjusted to 20:1:0.2 by measuring the dry weight of the fibre and calculating the required N and P fertilizers to be added.
As in the studies of pond dynamics, these high-fibre studies may first be done in tanks with neither fish nor bottom silt. This facilitates measurement of rates of conversion of these fibres to microbial and algal growth. As these paths are better understood, the silt and fish may be introduced in successive tests.
The Chinese experience has led to the use of polycultures containing as many as 8 or 9 compatible species having different food habits. It is possible that equally high rates of production can be achieved using a fewer number of appropriate species, or by monoculture; and that the disadvantages of producing a fewer number of species might be compensated by the savings in money and labour in producing, stocking, managing, harvesting and distributing a greater number of species, at least in certain areas.
It is recommended that experiments be conducted to compare the efficiencies of:
(1) monoculture of tilapia; (2) polyculture limited to 4 or 5 species; and (3) polycultures containing 8 or 9 species, as practised in China. Certain tilapias are known to be relatively omnivorous, and to feed on the bottom as well as all levels of the water column. In a polyculture of few species, all available feeding niches would appear to be filled by a combination of silver, bighead, grass and common carps, though tilapia might be added.
It is also recommended that such a limited polyculture be utilized in conducting experiments earlier recommended for comparing different manures, and different depths and areas of ponds. The ratio of species in such experimental populations should be rigidly standardized. For example, it might contain 5 silver carps to 1 bighead carp to 2 grass carps to 1 common carp, at a standard total density of 1 000 fish/mu.
To better understand the impact which silt has upon the pond ecosystem, a series of studies in the laboratory, in tanks, and in ponds will be made dealing with silt and pond water.
Laboratory analyses will consist of measuring: concentration of chemicals thought to be important in the pond ecosystem (N, NH3, P, K, Ca, Mg, CO3, Na, Cl, H2S); organic matter content of silt (as total volatile matter combusted at 550°C); redox potential across the water-silt interface; pH in water and in silt. To facilitate analysis, cores of silt will be taken in two or three specific locations in tanks or ponds from which the silt has been removed. Overlying water will be taken with the silt core to minimize disturbance of the interface. Sampling will start upon filling with water and will continue weekly throughout the growing season. In addition, rates of weight loss of standard fibre (cotton cloth woven of threads, having a weight of about 30 mg/metre is adequate) at the silt interface and in the water column will be measured continuously, with five days immersion time of the fibre in the tank or pond. These data will be analysed against weekly or fortnightly measurements of fish growth, with a view to determining whether there is a correlation between chemical or organic changes in the silt and fish growth.
There is the possibility that accumulation of extracellular production of mucopolysaccharides or of other metabolites may affect fish growth. If the more simple chemical and organic analyses outlined above do not show a correlation with measured trends in fish growth, or do not explain these trends, then chromatography of the water column and of interstitial water of the silt may be useful in revealing changes in concentrations of these organic molecules which may have an impact on fish growth.
Cycling of such key elements as N and P across the silt-water interface certainly is important to sustaining algal and microbial growth. Such cycling might best be initially studied in tanks with silt bottoms. Tank studies would permit use of radioactive labels. Transfer of P introduced into the water column or into the silt could be followed as it moves through the water-soil-biological system.
To Understand the relative effectiveness of silt as a crop fertilizer, the chemical and organic content of the silt will be correlated with crop growth using silt as a fertilizer. Comparative studies will be made of crop growth with the application of standard chemical fertilizers
Most of the studies described earlier involve experimental work in laboratories, outdoor tanks/pools, experimental plots, or experimental or commune farms. While some investigations would need only one type of facility, others may need more than one or all. Based on the nature of work involved they can be classified into some five groups.
The following are studies that should preferably be carried out in both the experimental ponds at the Centre, and in commune ponds.
(i) Evaluations of various types of manures or manure treatments in terms of both fish production and water quality.(ii) Fish diseases and mortalities as function of manuring.
(iii) Fish as carriers of pathogens.
(iv) Effects of supplementary feeding.
(v) Effects of aeration.
(vi) Fish stocking strategies (use of monocultures, limited polycultures and multi-species polycultures; use of different densities and combinations of species).
The studies that can be carried out in the experimental ponds at the Regional Lead Centre are:
(i) Silt production as a function of manuring.(ii) Evaluations of formulated feeds
(iii) Evaluations of those treatments given preliminary screening in the laboratory or in small pools (use of treated and untreated straw as substrates; testing of 'standardized' manure; evaluations of various manures, or treatments of manures, etc.).
(iv) Studies of biological and chemical processes on the pond bottom.
(v) Pond dynamics.
The following studies will have to be carried out in commune ponds.
(i) Study of the effects of pond depth and area, with special reference to influence on dissolved oxygen, other water quality parameters, and overall economics of pond operation.(ii) Evaluations of methods of manure management and application.
(iii) Economics of the use of land and other resources in integrated farms.
The investigations listed below can be carried out in the laboratory of the Centre:
(i) Determination of chemical and organic constituents of manures (green and animal).(ii) Study of treated and untreated straw (rates of digestion, colonization by bacteria, utilization by fishes, etc.).
(iii) Development of a 'standardized' manure formulated on the basis of desired levels of mineral and organic input.
(iv) Analyses of available by-products for formulation of a supplemental feed, and formulation and testing of same.
(v) Analyses and evaluations of silt constituents.
Some of the laboratory studies have to be followed up by yard or pool experiments, which include:
(i) Comparative evaluations of various manures - green, animal, fresh, composted and fermented (rates of decomposition, mineralization, and uptake by experimental fishes, and rates of fish growth).(ii) Evaluations of formulated feeds.
(iii) Use of treated and untreated straw as substrates.
(iv) Dynamics of silt-water interface.
In all investigations, particularly the experiments in the Centre and commune ponds, determination of costs (both direct and indirect) should form an integral element. This will enable evaluations and comparisons of the economic efficiencies of different procedures and systems of integration. Such data will be required for the construction of economic models of selected types of integrations that could be recommended for different countries or regions.
