4.1 Organic waste inputs
4.2 Fish species for culture
4.3 Water quality
4.4 Pond dynamics
4.5 Role of pond silt
4.6 Pond design
4.7 Fish disease and mortality
4.8 Fish as carriers of pathogens
4.9 Supplemental feeds
4.10 Economic modelling
The problems of research on integrated fish culture cover different disciplines concerned with crop, livestock and fish production. Obviously the Wuxi Centre cannot undertake research on all aspects. As indicated earlier the focus of studies has to be on fish culture. Since the main contributions of crop and livestock farming to fish culture are fish food and fertilizer and contribution of fish ponds to the rest of the farm is pond silt as fertilizer for crops and fodder plants, attention has to be directed toward the role of various farm products and wastes and the inter-relation between crops, livestock and fish. The Centre has to keep close liaison with relevant institutions doing research on crops and livestock and utilize the results of their studies as appropriate for both the design of experiments and interpretation of results.
4.1.1. Animal manure
4.1.2 Green manure
4.1.3 High fibre content substrates
(i) Comparative studies of the use of fresh and stored-fermented manure
There exist among fish farmers of different countries conflicting opinions as to the economic and other benefits of storing manure prior to its application to the pond. Fresh manure contains a complement of chemical and organic components with fermentation, inherent in storage, partly deletes. This loss is due to the natural inevitable production of biogas during storage. Whether or not the biogas (the main energy constituent is methane, CH4) produced during anaerobic storage and fermentation of manure is utilized, there is, during this storage-fermentation: (1) an inherent decrease of carbon; (2) an increase in ash; and (3) quite probably a loss of some volatile nitrogen compounds in the residual sludge and supernatant relative to the fresh manure. These three factors may result in lower fish yields per unit of available manure. However, benefits may accrue with fermentation. Biogas is produced; the fibres of the original manure may be partly digested and thus made more available for natural food production in the pond.
By selecting a given polyculture of fish capable of utilizing the range of natural foods believed to be abundant in manured ponds, a given moderately high stocking density, and a given type or source of manure, the production of fish in ponds receiving fresh manure and manure stored for specified periods (e.g., 15 days) will be compared. Relative yields of fish for these manuring systems will be measured. In conjunction with this, the potential value of biogas which might be obtained by fermentation will be considered in relation to the costs and labour involved in fermentation and biogas production. These data will permit an overall economic evaluation of the effectiveness and desirability of using fresh and stored manure for fish production.
The actual experiments can be performed at the Wuxi Lead Centre. Ponds of equal area and depth of approximately 400 m2, provide an adequate indication of what can be expected in larger commercial ponds. The smaller experimental ponds permit concurrent replications of selected pond treatments with considerably less investment in space and labour than would be required in larger ponds.
During these and other experiments, the full range of studies of pond dynamics, water quality, fish survival, fish disease, organic and chemical composition of the manure, etc., as discussed in later sections, will be conducted as an integral part of the programme. This multidisciplinary approach maximizes the range of data obtainable from each experiment, thus reducing cost and effort for achieving the overall goals of the Lead Centre. The interdisciplinary approach demands of scientists and technicians the utmost cooperation and consideration of each others' efforts.
(ii) Fish yield as a function of the type of manure
It may often be possible to grow a variety of animals on an integrated farm. However, the market demand and price for specific animals differs greatly from region to region. The effectiveness of various manures as substrates for growth of natural fish foods, and hence contribution to fish yield is likely not the same for all animals. The farmer on an integrated farm must select the combination of animals and fish that will give him the optimum total return on his efforts. Thus he must know what combined production of land animals and fish he can expect for a given feed input to the land animal.
To gain the necessary data to formulate this integrated animal-fish yield model, experiments in ponds will be conducted using a standardized polyculture suitable for manured ponds, with moderately high fish stocking density. Manures from pigs, cows, ducks and chickens will be used. If the number of available ponds permits, the animal manures will be tested concurrently with replications. If enough ponds are not available, the studies will be sequential with care taken to consider climatic differences during test periods. Fish and animal production will be correlated for each type of combination with total inputs of animal feed, labour and land utilization by ponds and pens. Manure production rate for each type of animal will also be measured.
As stated above, interdisciplinary studies will be conducted during all pond experiments. Each pond should yield data on a wide variety of aspects (pond dynamics, fish disease etc.), all of which benefit from this integrated experimental approach.
(iii) Fish yield as a function of land animal feed
The quality of a manure reflects, to some extent, the quality of the feed supplied to the animal. Since fish yield will be dependent upon the inputs to the pond, the combined fish-animal yield varies with changes in the land animal's diet. The type of feeds used differ very considerably among the climatic and economic environments of the countries served by the Wuxi Lead Centre.
To better understand the effect of feed on manure quality and potential fish production, the above described experiments using pig, cow, duck and chicken manures will be repeated using typical, animal feeds available to integrated farmers, ranging from high to low quality.
As previously mentioned, the range of dynamics of the manure-pond interactions will be studied.
(iv) Composition of manure and its relation to fish yield
Throughout the above experiments, the composition of the manure will be monitored. The parameters measured will include: manure biological oxygen demand or BOD (1 day at 30°C and also at local pond temperature), ammonia, Kjeldahl nitrogen, phosphate or phosphorous, potassium, percent dry matter (dried to constant weight at 70 to 100°C), percent volatile matter (combusted at 550°C in a muffle furnace). The volatile matter is a good indicator of the total organic substrate available for a microbial, heterotrophic food web. From time to time, measurements of lignin, crude fibre, not including lignin, and total fibre (crude fibre, lignin, hemicellulose) should be made. These measurements may be done at a feed analysis laboratory since they are not frequent.
The manure analysed in these studies will be from the yield experiments conducted at Wuxi Lead Centre. Comparison of the data describing composition of the manures with the measured fish yields from these experiments may show a correlation which will enable us to construct a model relating some features of manure composition to expected fish yield per unit quantity of the manure. This model, if it can be formulated, will permit the evaluation of a proposed integrated animal-fish or crop-animal-fish farm without the costly and time-consuming effort of actual pond experiments.
(v) Manure application and fish yields
There are differences of opinion on the most Suitable procedure for application of manure in fish ponds. It is believed that frequent applications, distributed over large areas of the pond surface, provide a uniform input of substrate for growth of natural fish foods. However, this requires special equipment and more effort than does application once in 10 days at one or only a few locations in the pond. The relative benefit of these approaches, such as saving of labour and increased fish yield must be quantitatively evaluated.
Because distribution cannot be realistically simulated in small ponds, these studies should be conducted on commercial commune ponds, preferably in the vicinity of the Lead Centre.
The distribution systems to be studied include:
(a) amount of manure/unit weight of fish biomass, e.g., kg manure (measured as dry organic matter)/kg fish
(b) frequency of manuring, e.g., once per day; once per week; once per 15 days
(c) distribution over pond, e.g., pile the manure in one or two locations; distribute by boat over most of the pond; distribute from one or two banks or through the water inlet.
(vi) Safe dosages of manure
Fish kill by anoxia, or loss of fish growth by low dissolved oxygen (DO), are two major risks in integrated farming. The oxygen demand of the manure uses pond DO. The mineral-chemical components of the manure stimulate phytoplankton growth. Phytoplankton produce oxygen during the day, but consume it during the night. Appropriate polyculture of fish can contribute to balanced growth of plankton. Changes in the DO cycle of a manured pond should be measured as a function of: manure BOD, fish polyculture, fish stocking density, pond temperature, and insolation (sunlight).
For all the above manure-fish yield experiments, the BOD of the added manure, pond temperature, and DO cycles will be monitored. From these data and the fish polyculture and fish density, correlations between the effects of given amounts of manure on pond DO, for specific pond condition (temperature, polyculture, density) will be sought. If such a relationship is found, safe amounts of manure can be recommended for given pond conditions.
Some researchers have found that BOD of fresh manure closely correlates with dry organic matter content of the manure. It this is consistent with data obtained in the Wuxi Lead Centre, then the easily measured parameter of dry matter percent may serve as an indicator of the manure BOD and hence as an indicator of the effect that the particular manure will have on a pond's DO regime.
(vii) Number of animals per unit area of pond
From the above experiments, the total amount of various types of manure that can be safely added to a unit area of pond will be derived. The manure production rate of pigs, cows, ducks and chickens on varied diets will also be measured. From these data, useful guidelines on the number of animals that can supply the required quantity Of manure to a given pond area (taking temperature, seasonal cloudiness and rain, fish polyculture and stocking density, animal feed quality, into account) will be derived. This will allow the integrated farmer to plan his fish pond-animal integration accordingly.
The input of green manure, or green fodder, is of obvious benefit in integrated fish farming, utilizing polycultures of a large variety of species, but: (1) its relative value as compared to animal manure; (2) benefit derived from its direct use as food; and (3) its influence as a manure in the production of natural foods (bacteria, protozoans, plankton, benthos, etc.), are not clearly known. Studies should be made of: (1) the relative value of green manure versus animal manures; (2) the relative value of various types of green manure (grass, vegetable tops, etc.); (3) their direct utilization as food, compared to their use as a manure; and (4) their relative value when applied fresh or when applied after composting.
(i) Treatment to increase digestibility
Substrates with high fibre content are often available in fair quantities in integrated farms. These substrates include among others rice straw, wheat straw and sugar cane waste (bagasse).
The cellulose of these substrates is often lined with lignin. This greatly reduces the rate at which these fibres can be digested by bacteria. Chopping the straw and partially hydrolysing it with weak sodium hydroxide (NaOH) has been reported to more than double the digestibility of straw in a cow's rumen. Since the processes in a pond may be similar to those in a rumen, treatment of these high-fibre substances may make them more useful as organic inputs to ponds.
To investigate the usefulness of the treatment, standard digestibility tests will be performed on treated and untreated samples of rice and wheat straws and on sugar cane waste. Treatment will consist of chopping the straw to 0.5 to 1 cm long pieces and moistening with 1 percent NaOH solution for 1 to 4 days at ambient temperatures and at 25°C.
Digestibility tests will be used to determine the available energy per unit weight as a function of original lignin, cellulose and hemicellulose. These tests will be conducted in vitro.
(ii) Fish growth in ponds with treated straw substrates
The effect of treated straws on fish growth can be measured in small ponds or large out-of-door tanks. Development of microbial growth on treated and untreated straws (bacteria, protozoa, nannoplankton) should be monitored. Straw contains low amounts of nitrogen and phosphate. These must be supplemented with chemical fertilizers to raise the C:N:P to approximately 20:1:0.5, which is considered good for microbial growth.
The Chinese experience has led to the use of polycultures containing as many as 8 or 9 compatible species having diverse food habits. It is not clear, however, whether such a practice has developed because it is significantly more productive than a polyculture containing fewer species. An efficient population must contain fishes that feed in all niches and consume the available foods. It is possible, however, that: (1) similar rate of production might be achieved using a fewer number of appropriate species; and (2) that the disadvantages of producing fewer species might be outweighed by the savings in cost and labour of producing, stocking, managing, harvesting, and distributing a greater number of species. In areas where the low-cost production of protein is more important than the variety of protein foods, it might be more efficient to produce fewer species, provided no significant loss in production or consumer acceptance is caused.
It is recommended that experiments be conducted to compare the efficiencies of monoculture, polyculture of 2 to 4 species, and polyculture of 6 to 9 fish species, as practised in China. For monoculture an omnivore or a species that feeds at several trophic levels Should be used. A possible choice in Wuxi would be tilapia. In limited polyculture, the available feeding niches would seem to be filled by a combination of silver carp, bighead carp, common carp, and tilapia. The ratio of species in such experimental populations should be standardized. For example, it might contain 20 percent silver carp with the remaining 80 percent being allotted to common carp and tilapia. The multispecies Chinese polyculture could include silver carp, bighead carp, tilapia, grass carp, Chinese bream, and common carp. This multispecies approach would require testing in ponds receiving animal manure only, and a combination of animal and green manure. For all the tests a standard stocking density, e.g., about 10 000 fish/ha, would be used. In ponds receiving animal plus green manure an increased density might also be tried to take advantage of the increased organic input.
Water quality should be monitored as a function of the various manure and polyculture treatments. Regular measurement should be made of important physico-chemical parameters.
(i) Physico-chemical parameters
Because of the importance of dissolved oxygen (DO) in manured ponds, this parameter should receive special attention. To better understand the DO regimes of the ponds, dissolved oxygen and temperature might be measured at several selected depth intervals at dawn, mid-morning and dusk several times each week. These data could be augmented by measuring over a 24-hour cycle the dissolved oxygen, temperature and pH. The following additional parameters should be measured weekly to give a more complete description of the pond chemistry: pond depth, pH, CO2, alkalinity, BOD, ammonia, nitrates, nitrites, and sodium orthophosphate.
Conductivity, hardness, suspended solids and settleable solids could be measured less frequently, possibly once each 21 or 30 days.
The seasonal cycle of pond water temperatures at just below the pond surface and at the pond bottom should be recorded in at least one large and one small pond.
Unless recorded elsewhere in the Wuxi area, continuous daily records should be kept of air temperature, cloud cover or (incidence of sunlight) wind velocity, humidity and rainfall.
At some point, an evaluation should be made of the effect of different types of aeration on water quality and fish production in waste-laden ponds.
A concerted effort should be made to identify or develop a reliable method, either chemical or biological, for indicating critical levels of dissolved oxygen. A biological method might utilize an indicator organism, such as a fish or a prawn, which would show distress at a higher level of dissolved oxygen than the cultured species. Additional possibilities might include: (1) quantities of phaeophytin as an indicator of senescence in the phytoplankton population; or (2) measures of chlorophyll-A, phytoplankton density, or level of organic nitrogen as indicators of high levels of oxygen demand.
(ii) Biological parameters
Phytoplankton and zooplankton population should be monitored in order to identify the species compositions and densities of populations occurring in ponds receiving different experimental treatments. Only limited measurements of primary production are recommended, but the phytoplankton communities should be characterized by measurements of phytoplankton densities, phytopigment concentrations, and by identifications and counts of the dominant species. It is recommended that: (1) phytoplankton study be made from no less than duplicate samples from each pond, that samples be collected at least bi-weekly or tri-weekly; and (2) that each sample contains depth-integrated water from the surface to the bottom of the euphotic zone.
The zooplankton communities should also be sampled bi-weekly or tri-weekly so that the relative densities of the major components (Cladocerans, copepods and rotifers) can be identified and related to other pond parameters. It is sometimes useful to measure species diversity of both phyto- and zooplankton as indicators of water quality. High species diversities of both types of plankton commonly reflect the good health of the community, whereas low species diversity may reflect stress, either from predation or poor water quality.
In making quantitative studies of plankton communities, pull-nets or cast-nets are of limited value since the quantity of water that passes through the net (e.g., prior to the net plugging) is uncertain. More precise is the technique of passing measured volumes of water (e.g., from a 10-litre pail) through screen nets of selected openings such as 37 microns (400 mesh) and 150 microns (100 mesh) to retain mainly phytoplankton and nauplii and zooplankton, respectively. Even with a 37 micron screen, about 90 percent of the phytoplankton pass through. Assessment of total phytoplankton requires a paper filter (Whatman No. 1 is usually adequate) and chlorophyll-A analyses.
The processes which convert manure into fish food have received considerable attention. The pond is a highly complex system. The temptation has been to measure many variables, usually with disappointing results. At the Lead Centre emphasis should be placed on rates of processes rather than measuring standing stocks of plankters and microbes. This implies attempts to decipher the energy flow within the pond.
The manure supplies chemicals for phytoplankton (autotrophs) growth and fibre substrate for a bacteria-protozoa (heterotroph) food web. Most of the past studies have concentrated on the plankton. Evidence is mounting that the bacteria-protozoa food web may be dominant in manured ponds. Rates of production of these micro-organisms and factors controlling these rates should be investigated. In addition, chemical transfer across the pond bottom-water interface should be studied. The attempt will be to identify the sites of food production in the manured pond and to learn how the pond environment can be modified to increase the number of sites or the productivity of the existing sites, so that the present limits of fish production based on manuring can be raised.
Silt taken from manured pond bottoms has traditionally been used as a fertilizer for field crops. The fertility of a pond is also thought to be related to the silt content of the bottom. Because of the considerable effort expended in silt removal, it would be useful to know quantitatively what the value of silt removal is to the pond and the value of silt application to a field.
Using the investigative approaches outlined above, the following will be studied:
(i) Biological and chemical processes at the pond bottom interface when the silt is present and after it is removed.
(ii) Effects of partial and total removal of silt on fish yield.
(iii) Effectiveness of silt as a fertilizer for land crops as compared with inorganic chemical fertilizers and manure. (It is understood that extensive experiments have been carried out by Agricultural Research Stations in China. The results of their work will be collected by the Centre.).
(iv) Chemical (content of N, P, K) or organic (amount of volatile matter) indicators of the quality of the silt as a fertilizer or a pond bottom substrate.
(v) Rate of production of silt as a function of manuring rate and fish stocking of a pond.
In view of differences of opinion on the optimum depth of ponds, and because of economic considerations inherent in pond construction, it is important to determine the relative productivity of ponds having depths in the range of 1.0-1.5 m, and those as deep as 2.5 m, found in China. Deeper ponds may well be necessary and justified in polyculture of several species, but may not be necessary in monocultures. Similarly, densely stocked and waste-laden ponds would need aerators for successful operations. It is necessary to determine these through appropriate experiments and observations.
Similarly, the influence of pond area is not sufficiently known, and should be investigated.
There is the possibility that the incidence of disease, or the mortality of fish due either to disease or loss of oxygen may be related to rates of manuring of ponds. In the course of the above described experiments records will be maintained of the incidence of disease and the rates of fish mortality in ponds receiving both animal and green manure. Analysis of the data related to incidence of disease and rates of mortality can include the total fish stocking density as well as the number of species in the particular experimental pond.
There is some possibility that handling or consumption of fish raised in integrated farms may cause certain health hazards. Studies should therefore be made of the incidence of bacteria, parasites and other potential pathogens (both external and internal) on the fresh carcasses of fish raised in waste-laden ponds. It is increasingly believed that the manured pond represents a hostile environment in which many potential pathogens cannot survive. If true, time may be a factor in their reduction or elimination. It is therefore recommended that such examination be made just prior to the harvesting and marketing of fish. Pond workers are regularly exposed to the organisms of the pond environment. Selected patheno-genic organisms in the water and on the pond bottom should also be monitored at regular intervals after filling the pond and after manuring.
It is a common practice in integrated fish farming to utilize so-called fine feeds, grass, certain aquatic plants, vegetable tops, and silkworm pupae as supplemental foods for fish. Such a practice not only involves a great deal of time and labour, but may not represent the most efficient use of such foods. It is possible that such available wastes or by-products could be formulated into a pelleted feed of high nutritional value. Such a properly formulated diet may promote faster fish growth, and be simpler to distribute. It is recommended that the formulation of such feeds using ingredients raised on integrated farms be undertaken by the Regional Lead Centre.
Perhaps the main reason for integrating fish farming with land animal husbandry and crop farming is the economic consequence that such integration will have on total farm production.
The entire range of the above experiments should be so designed as to provide the necessary data to construct an economic model of an integrated farm. The model will take into account specific local social, climatic, nutritional and economic conditions, and based on relations that will have been derived relating manure type and rate to fish yield, the model will project optimum allocation of available land area and labour among fish ponds, field crops and poultry or animal husbandry.
Specifically, combinations of fish-animal-crop (pig, cow, duck, chicken, wheat, rice, vegetable) and fish-animal (pig, cow, duck, chicken) will be dealt with. In the model, the weighting of actual values of each (the nutritional value of the food itself and the market value) and the interactive values (manure to the pond; silt to the field; crop waste to the pond) will be variable to satisfy the specific conditions of the regions served by the Wuxi Lead Centre.