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Use of organic residues in aquaculture

by John E. Bardach and Michael T. Santerre

The Range of Production in Aquaculture

Organic waste utilization in aquaculture can either be extensive, with wastes occurring naturally or being added, with little or no further production management (see Bardach, Ryther, McLarney, 1972), or it can be highly intensive under conditions where extraneous feeding and fertilization with inorganic plant nutrients play a major role in augmenting animal-protein yield from the system. Aquatic animal husbandry is pursued in embayments, ponds, rivers, lakes, raceways, in brackish water, fresh water, and full salinity ocean water. Many variants of extensive and intensive fish culture rely predominantly on the growing together of a few compatible species (poly-culture) to make fullest use of the various types of food present (plankton, bottom fauna) in a body of either natural or managed water.

The rationale of polyculture is obviously to divert as much as possible of the attainable biomass into channels that are useful to man, compared to those that prevail in a wholly natural food web. It should be pointed out that stocking fish in a lake does not necessarily increase the productivity of the lake, except for the productivity of harvestable (i.e., desirable) organisms. Where before the lake supported a complex food web ending in only a few harvestable fishes, and many other non-desirable (for human consumption) organisms, stocking with desirable fish fingerlings, as well as control of unwanted species, especially predators, diverts the biomass of the "non-suitable" species into production of a desirable fish biomass. It should be added, though, that monoculture, especially of molluscs in brackish water and of predatory fish, such as trout, salmon, or groupers, can furnish high annual yields that are commercially attractive in spite of substantial inputs; for these species, the food is extraneously supplied. The food webs of manured, fed, and fertilized polyculture ponds are exceedingly complex in comparison with cage monoculture systems.

A brief comparison of materials required for flow in ponds versus cage culture seems appropriate here. The principal pathways of nitrogen in ponds are illustrated in Figure 1. Possible nitrogen inputs in intensively managed polyculture ponds may be many and varied: atmospheric nitrogen; nitrogenous substances present in inflowing water; inorganic fertilizer nitrogen; organic waste nitrogen, and nitrogen present in feeds. Similar diversity is also present in losses of nitrogen from ponds. Measurement of nitrogen flow among the various nitrogen pools (e.g., dissolved nitrogen pool, bacterial nitrogen pool, etc.) is at best a difficult task, requiring sophisticated techniques. For the present, aquaculturists are utilizing information on a few such inputs, pathways, and pools, and are only very slowly evolving models allowing prediction of harvests of fish from a pond, given a specified set of conditions.

In contrast, cage culture represents a simplified ecosystem, and is the aquatic counterpart to high-density terrestrial husbandry systems, including cattle feedlots, chicken batteries, and so forth. Such production systems are fashioned to provide all of the environmental needs of the animal, and to maximize production per unit surface area. The cage system is quite simple: in it feed or food is supplied to the fish (usually monoculture, but polyculture cage culture is becoming more common), and feces, uneaten food, and waste metabolites are swept away from the cage by the continuous flow of fresh water. Cage culture, however, is generally more capital-intensive than pond culture, and requires a considerably higher degree of knowledge of the nutritional needs of the fish, as the aquaculturist often supplies the fish with their sole source of feed.

The fish-protein yield to man in natural waters of the temperate zone ranges from less than twenty to several hundred kg/ha (Figure 2). There are specific sites, often with inadvertent fertilization by run-off, where yields are much higher: a dead river arm in Hungary with a slow flow that also serves a duck farm produces 1.3 tons/ha/100 days, and a portion of Launa de Bay in the Philippines, the shallow recipient of much agricultural and domestic drainage, where the wind also concentrates the plankton, is capable of producing 3 tons or more of milkfish/ha/100 days; however, the site is now plagued with pollution from highly populated shores.

A comparable level of fish productivity prevails in the more typical fish ponds of Israel or India, albeit with more material inputs. Animal wastes are applied and often there is additional extraneous feeding; in these also, the 100-day yield reaches 3 - 4 tons/ha.

Figure 1. Principal pathways of nitrogen in a fish pond receiving organic wastes, fertilizer, and supplementary feed. The various trophic levels and relationships for animal biomass are not shown.

Figure 2. Comparison of yields of animal production systems (in kilograms per hectare per 100 days) and their corresponding grow-out densities (in numbers of animals per hectare).
¹ From: Bardach, Ryther, and McLarney, 1972;
² from: Delmendo, 1973 - 74;
³ from: Moav et al., 1977;
⁴ from: Buck, Baur, and Rose, 1978;
⁵ from: Ohia and Sinha, in press;
^6,7,8 from: personal communications with various experts in field (yields are for single horizontal, i,e., not multilevel, surface only).

Sewage oxidation ponds are also good bases for aquaculture: J. Ohia (in a personal communication) established that 2.5 tons/ha/100 days of several species of carp, mainly silver carp, can be grown if 200 m3 /ha/day of primary sewage effluent is added to the water (after settling of solids). The stocking of fish in sewage oxidation ponds is beneficial not only to fish culture, but to the waste treatment processes within the oxidation pond itself. Tilapia and silver carp were stocked in an oxidation pond and compared to an oxidation pond not containing fish (see Schroeder, 1975). Bacteria levels were lower in the pond containing fish (Table 1), perhaps because the disinfection potential of waters with high pH and greater oxygen content is greater. The high pH probably results in a higher rate of loss of ammonia to the atmosphere, considered to be beneficial from the waste-treatment viewpoint, and also from the viewpoint of fish health management (ammonia is toxic to fish). However, it represents a loss of valuable fixed-nitrogen fertilizer, and hence can be a somewhat negative trade-off.

The use of raw or primary treated sewage for fish ponds has been questioned for health reasons, but it should be noted that intestinal parasites and flora of man and other warm-blooded animals are anaerobic (or nearly so). Hence, the high oxygenation of fast-flowing water, of balanced sewage ponds, or of balanced fish ponds receiving organic wastes, does not permit the survival of most such pathogens (see Allen and Hepher, 1976). Thorough cooking of the fish provides an additional safeguard.

The addition of sewage to pond or river water, and the use of fertilization by means of animal wastes in aquaculture, are well-established and economically sound practices Higher yields per unit surface area are reached with other extraneous inputs, mainly by supplementary feeding and/or by forced water circulation, or even filtering. The main secret of success in achieving up to several hundred tons/ha annual fish production (often extrapolated from smaller surface areas) lies in the use of natural fast-flowing water or artificially constructed systems in which many thousands of fish can be stocked and fed. Similarly, cage-reared fish in strong tidal flows can achieve phenomenal rates of growth and production. They are fed with compounded feed(however expensive), with trash fish, with household wastes, or with cereals, cereal wastes, or other agricultural residues. Attractive economic returns occasioned by cultural food tastes invite these practices (see Bardach, Ryther, and McLarney, 1972, Chapter 1).

TABLE 1: Measured chemical and biological parameters in waste treatment ponds
[with (+) or without (-) liquid cow manure, and with (+) or without (-) polyculture (tilapia, carp) fish]

(From: Schroeder, 1975)

The Value of Organic Wastes

In a polyculture fish farm in Israel, as one instance, the yields are reasonably high (4,1 50 kg/ha/yr) Obviously, savings could accrue if manure were used instead of inorganic fertilizer (depending, of course, on nearby production and low-cost handling of manure). Just how economic- albeit site- and condition-specific-sewage-fed aquaculture can be, is exemplified by a comparison of energy accounting of the above-mentioned Israeli operation with the Indonesian cage culture of carp in sewage-fed streams, and pond-grown carp near Munich that derive their sustenance from a mixture of Munich sewage and the water of the Isar River. In Israeli pond polyculture 65 Kcals (representing fixed and variable production inputs excluding labour) produce one gram of protein; this could be reduced to about 50 Kcal/g if the industrial fertilizer were replaced with manure. In contrast, the sewage-based carp culture in flowing water in Indonesia, as well as that in Bavaria, require only 4 - 10 Kcals/g of protein. Channel catfish and chickens are less efficient, requiring approximately twice the calorie input per gram of protein above that used in Israeli polyculture and 14 to 37 times that of pure sewage-based carp culture (see Rawitscher and Mayer, 1977). It should be noted that in polyculture nutrients are reused as they pass through the digestive tracts of the various component species.

The use of manure and domestic sewage, however, represents a saving for the fish farmer only when these materials are available, and when, because of their inherent bulk, they do not have to be transported very far. Their use prevails in many parts of tropical Asia, in India, in communes in China, and in the kibbutzes of Israel, where land-animal husbandry and aquaculture are practiced conjointly (see Tapiador et al., 1977; Allen and Hepher, 1976; Yashouv, 1966). Examples of this are provided by a hog-cum-fish polyculture experiment (see Buck et al., 1978), and by a study comparing biomass harvest of an oyster-only culture system, and an oyster-cum-detritus feeder system (see Tenor, Browne, and Chesney, 1974). In the hog-cumfish system (Figure 3), overall productivity of biomass was increased by 67 per cent-with no additional feeding or fertilizer-by providing swine wastes (uneaten food, feces, urine) to a polyculture pond. Feed conversion efficiency increased from 3.8:1 in the hog-only system to 2.2:1 in the hog-cum-fish system. Conversion of feed nitrogen (our extrapolation) was 58 per cent in the hog-only system, versus 70 per cent in the hog-cum-fish system.

The addition of a detritus-feeder (a polychaete worm) to an algae-oyster culture system (Figure 4) increased biomass conversion efficiency for an oyster-cum-worm polyculture system (see Tenore, Browne, and Chesney, 1974).

Anaerobic digestion has been reported to increase manure ammonia content (manure being a preferred kind of agricultural nitrogen fertilizer), from 26 per cent in raw unprocessed manure, to 50 per cent following treatment (see Sanghi and Day, 1977). However, the extent to which anaerobically-treated sludge and supernatant can be substituted for untreated manure in a fish pond and still maintain high yields of fish has not been demonstrated. This is a very important consideration, because organic substances added to a pond can be consumed directly by heterotrophic organisms and by-pass the photosynthetic production level. Thus, production of fish using organic manures can greatly exceed levels predicted for a pond based entirely on an ecosystem starting with light-limited plants that utilize inorganic nutrients.

Certain special conditions of combined aquaculture and land-animal husbandry have been devised that reduce to a minimum the difficulties and costs of handling organic manures, and that benefit both husbandry components. Ducks are natural manure carriers, as it were, and in duck-cum-fish culture in Hungary, ducks are stocked in ponds after the fish have reached fingerling size. The presence of ducks leads to an increase in fish biomass of 0.3 to 0.4 tons/ha over conventional ponds without ducks (Mueller in a personal communication). The ducks in this case are selectively bred to reach their market size of 2.5 kg in 45 days by copious feedings with a special pellet diet. Also, sheds and runways for ducks are necessary, as is skill in poultry-keeping in addition to that in aquaculture. Furthermore, intensive use of the fish ponds by ducks can threaten the pond walls. Care must also be exercised not to overload the aquatic ecosystem with excrete and thus bring about highly anaerobic conditions in the bottom mud, which is the nursery ground of many invertebrates that serve as important food components to the fish. Despite these possible problems, mutual benefits to fish and bird-rearing are many, including: lower capital investment than that for intensive chicken culture; shortened growing time for ducks; better utilization of feeds (ducks eat organisms not ordinarily eaten by fish, for example, aquatic weeds, frogs, etc.); ducks distribute manure evenly throughout the pond; and fish-pond ducks are healthier, leaner, and have cleaner feathers than ducks raised in other, conventional production systems (see Woynarovich, 1976).

Figure 3. Efficiencies of conversion of feed, feed nitrogen (extrapolated), and feed calories (extrapolation) of a hog-only system and a hog-cum-fish polyculture system. (After: Buck, Baur, and Rose, 1978; plus our calculations.)

Figure 4. Materials flow, harvest levels, and conversion efficiencies of an experimental sewage aquaculture system. (After: Tenore, Browne, and Chesney, 1974; plus our calculations.)

Another pattern for land and water animal rearing presents itself in the placing of pigsties partially over the ponds, in such fashion that wastes from the pig platform can be sloshed down into the ponds. This technique has been pioneered in Malaysia, where water hyacinths grown on part of the pond surface are incorporated into the pigfeed and where fertile pond water is also used to water market garden crops (see Ho, 1961; Figure 5). Such integrated farming systems that can amortize themselves and bear profit after three years depend, of course, on year-round availability of water and on a suitably sloped terrain.

Direct Feeding

Feeding types among fishes range from predatory gulpers to sifters of organic materials in mud, to zooplankton feeders, and to herbivores that eat algae or even leafy plants. As already intimated, the rationale of polyculture is the selection of compatible species with different feeding habits. In addition, as fish learn to feed on almost anything, it is relatively easy to develop pelleted foods for fish culture, dietary quality considerations aside. At the same time, such catholic feeding habits permit the use of plant materials, especially cheap or nearly valueless crop residues (bran, etc.). Table 2 (from Bardach, 1978) illustrates this, as does the practice of building very wide pond margins around the fish ponds in China for cultivating grasses where leafy-plant-feeding grass carp (Ctenophryagodon idella) comprise about 20 per cent of the stock in the pond (see Tapiador et al., 1977).

All sorts of other wastes, even sludge, are fed to fish (see Kerns and Roelofs, 1977; Viola, 1977; Bayne et al., 1976) with very low conversion efficiencies, to be sure, but presumably favouring cheap production costs nonetheless (Table 3).

Carnivores make up a certain proportion of polyculture components; in fact various traditional aquaculture schemes incorporate a few voracious predators, albeit under intensively supervised management conditions, for example, pike in common carp ponds and wels (Silurus glanis) in poly-culture carp ponds (see Bardach, Ryther, and McLarney, 1972; Rutka in a personal communication). Sometimes pure carnivore culture is practiced with reliance on the availability of so-called trash fish, that is, species too small to be eaten directly, or unacceptable as table fare. The culture of groupers in various parts of the Pacific and of yellowtail in the Inland Sea of Japan is based on the availability of this kind of high-protein feed; it is mentioned here because one sometimes hears the argument that such practices are ecologically unsound. They may appear so at first glance, but these comments usually do not take into consideration that aquaculture is pursued to gain a livelihood.

Figure 5. Integrated aqua-agricultural system used in Singapore. {After: Ho, 1961).

TABLE 2 Proximate composition of feedstuffs used in fish culture

(From: Bardach, 1978)

TABLE 3: Yields of fish for various residues used in China

(Based on information given to members of a study mission; after: Tapiador et al., 1977; conversion efficiencies are our estimates.)

The future prospects for the increased use of organic wastes in aquaculture (especially as fertilizers) are clearly influenced by the cost of chemical fertilizers. As the price of fertilizer increases as fossil fuel costs rise, one can anticipate greatly increased use of organic wastes in aquaculture even without vigorous promotion. Certain key research needs to be undertaken to make such use as beneficial as possible. These investigations should relate to the big-economics of combined agro-aquacultural systems with a view to establishing trade-off values between the use of manure in aquaculture against other agricultural/domestic purposes. The organic value of various wastes, and the cost of handling and treating them under various levels of intensity of operation and development need to be established. Health problems related to the use of sewage also need attention, especially as they relate to cost trade-offs and permissible risks under various treatment and handling conditions. Questions of the environment need to be addressed vigorously; as the pressure on water supplies increases overall, fish ponds may be used increasingly for human water supply. Multiple-use oxidation ponds that supply animal protein and furnish domestic water will also increase, and problems of eutrophication and contamination of ground and surface waters need to be addressed. The need for interdisciplinary research is obvious if one wishes to make the best use of the trade-offs among the several possible goals of fish-pond use described here.

One more caveat seems necessary about aquaculture in general, but more specifically about the seemingly simple but really complex subject matter of the use of organic residues in aquatic animal husbandry. This warning is also a challenge embodied in the quotation (from Matsuda, 1978) that stresses, by implication, the need for multiple-level research, with strong emphasis on pilot installations and culture-oriented extension: "Aquaculture is not solely a matter of growing a product; it is also a part of rural development, including marketing, distribution of food and income, employment and living conditions. Thus aquaculture should not be recommended indiscriminately to people who are not ready for it."

References

1. Allen, G.H., and Hepher, B., "Recycling of Wastes through Aquaculture and Constraints to Wider Application," FAO Technical Conference on Aquaculture, Kyoto, Japan, 26 May-2 June 1976, FIR: AQ/Conf/76/R. 19.

2. Bardach, J.E., in CRC Handbook, Energy in Aquaculture, D. Pimentel, ea., CRC Press, West Palm Beach, Florida, in press.

3. Bardach, J.E., in Ecology of Freshwater Fish Production, S.D. Gerking, ed. Oxford, England: Blackwell Scientific Publications, 1978.

4. Bardach, J.E., Ryther, J.H., and McLarney, W.O., Aquaculture: the Farming and Husbandry of Freshwater and Marine Organisms, New York: John Wiley & Sons, 1972.

5. Bayne, D. R., Dunseth, D., and Ramirios, C.G., "Supplemental Feeds Containing Coffee Pulp for Rearing Tilapia in Central America," Aquaculture 7, pp. 133 - 46, 1976.

6. Buck, H.D., Baur, R.J., and Rose, C.R., "Utilization of Swine Manure in a polyculture of Asian and North American Fishes," Trans. Am. Fish. Sco., 107(1), pp. 216 - 22, 1978.

7. Delmendo, M.M., "The Plankton of Laguna de Bay, the Primary Basis of Milkfish Farming in Enclosures in the Areas," Philippine Agriculturist 57 (7-8), pp. 335 - 42, 1973 - 74.

8. Ho, R., "Mixed Farming and Multiple Cropping in Malaya," Proceedings of the Symposium on Land Use and Mineral Deposits in Hong Kong, Southern China, and Southeast Asia, Paper No. 11, pp. 88 - 104, 1961.

9. Kerns, C.L., and Roelofs, E.W., "Poultry Wastes in the Diet of Israeli Carp," Bamidgeh 29 (4), pp. 125 - 35, 1977.

10. Matsuda, Y., "The Growth of Aquaculture in Developing Countries: Potentials, Patterns, and Pitfalls," Fisheries 3 (4), pp. 2 - 6, 1978.

11. Moav, R., Wohlfarth, G., Schroeder, G. L., Hulata, G., and Barash, H., "Intensive polyculture of Fish in Freshwater Ponds. I. Substitution of Expensive Feeds by Liquid Cow Manure," Aquaculture 10, pp. 25 43, 1977,

12. Ohla, J. and Sinha, R., in press.

13. Rawitscher, M. and Mayer, J., "Nutritional Outputs and Energy Inputs in Seafood," Science 198, pp. 261 - 64,1977.

14. Sanghi, A.K. and Day, D., in Agriculture and Energy, W. Lockeretz, ea., New York: Academic Press, 1977.

15. Schroeder, G.L., "Some Effects of Stocking Fish in Waste Treatment Ponds," Water Res. 9, pp. 591 - 93, 1975.

16. Tenore, K.R., Browne, M.G., and Chesney, E.J. Jr., "Polyspecies Aquaculture Systems: the Detrital Trophic Level," J. Mar. Res. 32 (3), pp. 425-32, 1974.

17. Viola, S., "Energy Value of Feedstuffs for Carp," Bamidgeh 29 (1), pp. 29-30, 1977.

18. Woynarovich, E., "The Feasibility of Combining Animal Husbandry with Fish Farming, with Special Reference to Duck and Pig Production," FAO Technical Conference on Aquaculture, Kyoto, Japan, 26 May-2 June 1976, FIR: AQ/Conf/76/ R. 6, 11 p.

19. Yashouv, A., "Mixed Fish Culture-an Ecological Approach to Increase Pond Productivity," FAO World Symposium on Warm Water Pond Fish Culture, Rome, 18 - 25 May 1966, FR: V/R-2.

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