The most important freshwater culturable fishes of Pakistan are the "major Indian carps like ‘Rohu’ (Labeo rohita), ‘Thaila’ (Catla catla) and ‘Mori’ (Cirrhina mrigala) Fig. 1. (1.1 to 1.3)
Fig: 1.1 Labeo rohita
Fig: 1.2. Catla catla
Fig: 1.3. Cirrhina mrigala
Source: Qureshi, 1965.
These fish are herbivorous in nature and are very selective about their food. Major carps are the best example of a polyculture system because they do not compete with one another for food i.e. Catla get their food at the surface layer, Rohu from the midlayer and mrigal at the bottom of the pond. Some exotic species like Gulfa (Cyprinus carpio), Grass carp (Ctenopharyngodon idella), Sarotherodon mossambica and trout species (Fig. 2) (2.1 to 2.5) are also cultured in Pakistan.
Fig: 2.1. Carp (Cyprinus carpio)
Fig: 2.2. Ctenopharyngodon idella
Fig: 2.3 Sarotherodon mossambica
Fig: 2.4 Rainbow trout (Salmo gairdneri)
Fig: 2.5 Brown trout (Salmo trutta)
Source: MidGalski and Fichter, 1977.
The other important freshwater fish of Pakistan are catfish like Mullee (Wallago attu), Khagga, (Rita rita), Singhi or Lohar (Heteropneustes fossilis), Jhangur (Clarias batrachus) and Mystus Spp. (Fig.3) catfish (3.1 to 3.6).
Fig: 3.1. Wallago attu
Fig: 3.2. Rita rita
Fig: 3.3. Heteropneustes fossilis
Fig: 3.4. Clarias batrachus
Fig: 3.5. Mystus oar (Singharee)
Fig: 3.6. Mystus seenghala (Singhara)
Source: Qureshi, 1965.
Catfishes are carnivorous in nature. In Europe and certain Asian countries, these are successfully cultured in ponds, raceways, cages and aquaria by feeding animal wastes directly or indirectly, but no such success has been achieved in Pakistan.
Feeding animal wastes to fish is an old practice. The mechanism of manure fish recycling is illustrated in (Fig. 4).
Fig. 4: Production cycle of fish in fresh water. Source: Huet, 1975.
A fish is the final result of a complex biological cycle. The chain or cycle of natural fish production includes the following links: (a) mineral nutrients; (b) plant production (c) intermediate animal consumption and production leading to the final product which is the fish; and (d) reduction. The origin of this cycle lies in the mineral nutrients of water which come from soluble substances, carried to the water by exogenous detritus (animal waste) and also by rain-fall. By means of photosynthesis, the green vegetation transforms these inorganic substances into organic matter which forms vegetable tissue (higher & lower plants). Living or dead, the plants are consumed by numerous small animals. These then serve as a food for larger water animals which in turn (as well as the smallest of them and also certain type of vegetation, both living or dead; are eaten by fish.
The last stage is the reduction which is brought about by bacteria. Bacteria, by a mineralization mechanism permits the return in solution of all dead components of organic matter—vegetable and animals and their re-integration into the biological cycle.
The production of fish pond depends, in the final analysis, on the production of vegetation which in turn is dependent on the nutrients found in the pond. If it is desirable to increase the production of cultivated fish by giving them greater quantities of natural food, it is not possible to do so directly. It is first necessary to increase the vegetable growth on which the animal (microfauna) feed. The vegetable growth of the fish pond can be increased by introducing fertilizers and animal manures.
Integrated fish-culture with livestock raising has been well-developed in China, Hungary, Germany, Malaysia and certain other countries (Hickling, 1960; Wolny, 1966; Ling, 1971; Tapiador, et al. 1977; Woynarovich, 1979). Little attention has been paid to the recycling of animal wastes through fish production in India and Pakistan, but cattle manure is used for fertilizing fish(nursery, rearing and stocking) ponds (Alikhuni, 1957; Sharma 1974; Jhingran 1974). In India, attempts have been made in recent years to combine livestock raising with fish culture and to standardize the number of animals required per unit of water area for adequate manuring and high fish yields in the absence of fertilizers and supplemental feed. The integration of pig and duck farming with fish culture was attempted for the first time in India in Nadia district, West Bengal (Sharma, et al. 1972a, 1979b). In Pakistan, no such work has been done on scientific lines and this practice is restricted only to certain private farms.
The manuring of fish ponds as a means of increasing fish production was known in China in the fourth and fifth centuries B.C. (Neess, 1949) but the use of chemical fertilizers for the same purpose has only recently been developed. Integration of fish culture with livestock and crop farming is an ancient practice in China. The concept of an all-round development of agriculture, animal husbandry, fisheries and other sideline occupations widely adopted in modern China has resulted in different patterns of integration throughout the country. This is probably the most impressive aspect of Chinese aquaculture and of considerable value to other countries, particularly developing countries interested in integrated rural development.
The major species used in integrated fish farming in China are herbivorous and omnivorous especially carps and tilapias. Animals raised in integrated farms are pig, (3500 kg of manure slurry/pig), 25–45 pig/hac in China) ducks, cattle, sheep and chicken. It is estimated that 20,000 ducks produce 1000 tonnes of manure/year. Experiment conducted in Alabama (USA) by Swingle and Smith, 1939) yielded considerable information on the effect of fertilizers, especially inorganic ones under temperate climatic conditions. The fish carrying capacity of ponds in Alabama is increased by 300 to 400% as a result of fertilization.
Weib, (1930) studied the effect of organic and inorganic fertilizers on the production of planktons in North America. Hogan (1933) and Meehean (1934) showed an increase in the production of fish due to fertilization. Judy and Schloemer (1938) found that both plankton abundance and fish growth rate increased after the application of fertilizers. Howell (1942) concluded that fertilization led to increase in plankton abundance and fish production. Smith and Swingle (1943) also studied the effects of both inorganic and organic fertilizers on plankton life and found an increase in plankton as well as fish production. Lackey and Sawyer (1945) studied the relationship of biological activity and inorganic nitrogen concentrations in the water and showed that plankton productivity is related to fertilization. Surber (1945) noted the effects of various fertilizers on plant growth and their probable influence on the production of small mouth Blackbass in hard-water ponds. Edmondson and Edmondson (1947) proved that fertilization with phosphate alone or phosphate and nitrate increases phytoplankton production and they also concluded that the rate of oxygen production through photosynthesis increased after fertilization by a factor of about 1.5–5.
Swingle (1947) summarised previously published fertilization data. Surber (1947) conducted experiments and noted variation in nitrogen content and fish production in smallmouth blackbass ponds.
In pond water a 4:2:1:8 ratio of N-P-K-CaCO3 (mixture of commercial fertilizer) gave a fish production of 578 lb/acre as compared to 124 lb/acre in the unfertilized control tank (Hora, 1943). Smith (1948) fertilized a natural lake with N-P-K and obtained an increase in plankton production. Ball (1949) obtained greater production of plankton, bottom organism and fish by using both organic and inorganic fertilizers in the hatchery ponds. Plankton production was increased by many times as a result of fertilization (Matida, 1955). Langford (1950) and Ball and Tanner (1951) found that both plankton and fish production are increased with the addition of fertilizers.
According to Sklower (1951), cow and pig manure are by far the most common manure used in fish pond work. These are valuable in conditioning the soil of new ponds and provide a ready made mass of organic matter, containing the necessary nutrients. Tanner (1960) studied the chemical and physical effects of inorganic N-P-K fertilizers added to natural lakes. A significant effect of fertilization and feeding of fish was seen by Shimadate (1957) who noted higher fish production due to fertilization. Hepher (1962) conducted experiments on the fertilization of fish ponds in Israel for ten years and found positive effect on the growth of fish. Prowise (1961) and Mortimer (1954) fertilized the fish ponds and saw the effect of fertilizers on the fish production. Similarly, Padlan (1960) stated that fertilization is a key to higher fish production. It has been reported by Oguyama et al. (1962) that pond productivity can be improved by fertilization.
Hora (1943) states that animal life in a pond depends to a large extent on the phytoplankton for its supply of organic food. It would thus seem obvious that the bulk of animals is roughly proportional to the bulk of vegetation on which they directly or indirectly graze.
It is a common knowledge among pisciculturists of Europe, America, Japan and China that a pond receiving a considerable influx of animal and human excrement shows 3 to 10 times more rapid growth of carps than a pond without such an influx. Washings of the farmyard and wine are usually drained directly into fishery ponds. These, being rich in nitrogenous substances, help in the growth of phytoplankton. Cowdung or pig faeces are also eaten by certain fish in the raw condition.
Reich, (1950) noted that phosphorus disappears rapidly within two days after fertilization. This rapid decline in phosphorus concentration after fertilization was also noted by Nisbet (1951) and Zeller (1952).
Schroeder (1977) carried out experiments on the intensive use of organic animal wastes (fluid cowdung) for the culture of micro-organisms in fish ponds to replace part or all of the additional food requirements.
In all cases, the use of such organic wastes resulted in large increases in the yield of fish per unit area of the pond and sharp decrease in the food like valuable grains and fishmeal which had to be added in the pond to produce one kg of fish.
Different countries have obtained more than satisfactory production. Staggering yields of 3,600 to 17,800 kg/ha were reported from Bangkhen farm in Thailand (Pohgsuwana, 1957) by the application of fertilizers. Hurvitz, (1960) records individual yields of 4,300 kg/ha from ponds in Heftsibah area of Israel.
Ahmed (1979), Yasmeen (1979) and Najeeb (1980) prepared different kinds of artificial feeds and applied them successfully for gaining a satisfactory growth rate of fish even under controlled conditions.
Bajwa (1981) tested the effect of cowdung on the growth of fish (Cyprinus carpio) and concluded that the application of cowdung in fish ponds increases the fish production.
Krishnamoorthi and Abdulappa (1977) reported that fish ponds fertilized with sewage and sewage effluents have shown encouraging results of fish growth and harvest. He also mentioned that the growth of carps (i.e. Labeo rohita and Cyprinus carpio) was faster as compared to the air-breathers (i.e. Heteropneustes fossilis, Clarias batrachus (cat fish) and Channa marulius but the air-breathers are most suited from the point of view of nocturnal depletion of dissolved oxygen.
Cattle-fish farming is practised in Israel where cattle manure is collected from stalls and stored in tanks near the ponds for later application. Schroeder (1978) reported that using organic manure as the sole nutrient in fish ponds gave 75% of the yields attained by using supplemental grain feeds and 60% of the yields attained by using protein enriched pellets. Manure applied at the rate of 200 to 1,000 kg/ha/day increased fish yields from less than 500 to more than 4,000 kg/ha representing fish growth of 20–40 kg/ha/day without supplemental feeding. Intensive use of manure in conventionally fed fish ponds doubled the fish yields with half the normal supplemental feed requirements. Sufficient growth of zooplankton and phytoplankton can be ensured by application of fresh or semi-dried cowdung at the rate of 11,200 kg/ha/annum (Hora and Pillay (1962). In Israel, it is considered safe to use 75–100 kg/ha/day DOM (dry organic matter) of manure. The cowdung is placed at the corner of the pond in such a way that it gradually diffuses into the pond to promote the growth of plankton. If, thereby, pollution is apprehended, a separate small pond can be exclusively used for the production of plankton.
Best results are obtained when cowdung and superphosphate are applied in the ratio of 3:1 (Hora and Pillay (1962). 100 kg organic manure (cowdung, duck and chicken droppings) contain 8 kg carbon which can produce 15–16 kg algae and 3–4 kg fish. Therefore, by applying 12,500 kg cowdung per ha per annum, we obtain 500 kg fish from one ha pond, worth Rs. 10,000.
Both Israel and China demonstrated that it is possible to utilize aeration, supplementary feeding, multiple stocking and cropping and other intensive methods to achieve experimental production rates as high as 18,000 kg/ha/year, but average rates of sustained production throughout most of the world are probably in the range of 300–500 kg/hectare.
Many farmers report that despite all the improvements, including the use of aerators, production through manuring alone reaches a plateau after a certain stage where further increase is possible only through supplementary feeding. This indicates the need for formulating and preparing suitable supplementary feeds, preferably based on ingredients produced on the farm.
Since the organisms that develop in the pond through indirect feeding are rich in protein (50–60% dry weight) simple, carbohydrate-rich crop wastes can be used as direct feed for fish. Thus, the natural protein-rich organisms developed as a result of indirect feeding can be supplemented with nutritionally poor wastes such as rice bran to increase fish production in the pond. The combination of direct and indirect feeding allows utilization of both animal manures and some agricultural residues to give high yields of fish. Jhingran and Khan (1979) reported from India that an initial application of 10,000 to 15,000 kg/ha of cowdung is the best and cheapest manure for fish ponds. Spaced manuring with an initial dose of 10,000 kg of cowdung/ha, 15 days before the anticipated date of releasing fry in the nurseries and 5,000 kg/ha 7 days after stocking is said to promote a sustained production of zooplankton. Experiments have shown that the addition of manganese (as MnSO4, H2O) at the rate of 1 kg/ha, after a basal dose of 20 kg P2O5/ha, markedly increased the plankton production in ponds. When superphosphate mixed with cattledung, is used for fertilizing nursery ponds, an average survival rate of 45% from the larval to fry stage is obtained with a stocking density of 6 million carp larvae/ha.
The initial dose of fertilizer, on the day preceding stocking, consists of 150 kg of superphosphate of lime, 50 kg of triple phosphate of lime + 700 kg cowdung or any dung + 700 kg of oilcake. All these four types of manure are mixed together thoroughly by adding sufficient water to make a thick paste and then broadcast throughout the nursery. The nursery is then inoculated with 30–50 ml of Daphnia and Moina. On the second day of stocking, oilcake and cattle-dung are applied at the rate of 350 kg and 87.5 kg/ha, respectively. In parts of Bangladesh, a 3:1 mixture of cowdung and superphosphate is used at 555 kg/ha/year. (Bardach et al. 1972).
At the pond Culture Division of the Central Inland Fisheries Research Institute, Barrakpore, the rearing ponds were manured with cowdung at the rate of: 11,230 kg per ha, 10 days before stocking, ammonium sulphate + single super phosphate + Calcium ammonium nitrate (11-5-1) at the rate of 690 kg/ha two months after stocking with fry.
For production ponds one recommended does is 1000 kg or more of cattle dung, 560 to 1200 kg of poultry manure and 5,000 kg of green compost per hactare. For the use of inorganic fertilizers, the standard combination of N:P:K at 18:8:4 is generally recommended.
At the pond Culture Division of the Central Inland Fisheries Research Institute, a mixture of organic manure (Cowdung @ 20,000–25,000 kg/ha/year in 7–11 instalments) and inorganic fertilizers (ammonium sulphate + single superphosphate + Calcium nitrate in the ratio of 11:5:1 @ 1380–1725 kg/ha/year in 4–10 instalments) has given encouraging results.
Varghese, et al. (1980) demonstrated a polyculture system of silver carp (Hypophthalamichthys molitrix), grass carp, (Ctenopharyngodon idella), Common carp (Cyprinus carpio), Rohu (Labeo rohita) and mrigal (Cirrhina mrigala) for ponds of India. The pond of 0.12 ha was fertilized with cattle faeces - 800 kg, Superphosphate-5 kg and urea - 5 kg twenty days before being stocked with fish. The pond was again fertilized with cattle faeces (400 kg) superphosphate (6 kg) and urea (4 kg) fourty five days after stocking and every month after that. The fish were fed 6 days a week with rice bran: oil cake (1:1) at 2% of body weight. The grass carp got Hydrilla 2 kg daily in the 1st month, 3 kg in the 2nd and 3rd months and 5 kg in last 3 months with hybrid napier occasionally. The profit obtained was calculated as Rs. 1025.40, above 137% of the operating cost or 57.8% of gross income while the cost of production was Rs. 2.33/kg fish. In Karnataka, India, Singit et al. (1980) also developed a composit fish culture system of mrigal (Cirrhina mrigala), Common carp, milk fish (Chanos chanos), Catla (Catla catla), rohu (Labeo rohita), grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalamichthys molitrix) by manuring ponds with cattle faeces, superphosphate and urea. Fish were also fed with rice bran and oil-cake as a supplementary food. The profit was first calculated as Rs. 1427 or 71% of operating cost and 41.5% of gross income. The cost of production was Rs. 2.76/kg of fish.
Sinha (1979) developed a successful system of polyculture of three main Indian carps, Catla catla, Labeo rohita and Cirrhina mrigala with the Chinese carp Hypophthalamichthys molitrix (Silver carp), Ctenopharyngodon idella (grass carp) and Cyprinus carpio (Common carp) by manuring ponds with inorganic and organic fertilizer. Rice bran or wheat bran and oil cake were used as supplementary feed. Grass carp was fed with aquatic weeds. In research centres, yields from 2569 kg/ha (in six months) to 5162 kg/ha (in six and a half months) have been obtained. Ordinary ponds give 200–500 kg/ha of fish a year. Trials show yields of 1053 kg/ha/annum without using supplementary feed or fertilizer, 1398–2303 kg/ha/annum with fertilizer, 3314–4005 kg/ha/year with supplementary feed and 4244–5506 kg/ha/year with fertilizer and feed.
Meyers (1977) through intensive aquaculture in Israel, fed cattle manure into fish ponds at daily rates of 250–400 litre/tonne of fish biomass, increasing fish production ten times (from 0.5 tonne to 5 tonnes per ha). Other experiments of Meyers involving the use of cattle manure supplemented with chemical fertilizers are summarised in the table-1
The yields of Common Carp and Tilapia indicate that the potential of livestock manure in this production is of great magnitude.
Table 1: Growth of fish in manured ponds1(110 days)
|Parameter||Unit||Common carp||Tilapia||Silver carp|
|Initial size of fish||(g)||20||50||30|
|Size of fish at harvest||(g)||500||300||800|
|Total amount of harvest||(kg/ha)||2,500||1,500||400|
|Calculated harvest per year||(kg/ha)||8,295||4,977||1,327|
1 Manure added five times per week, supplemented with superphosphate (20% P) and ammonium (20% N) at 60 kg/ha/2 weeks.
Source: Meyers, 1977.
According to Pullin and Shehadeh (1980), organic matter of Cow manure should be added to the pond at a daily rate of 3–4% of the standing fish biomass. Chicken manuring rates may be lower, 2.5–4.0%. At this manuring rate, with a polyculture of 9,000 fish/ha, the fish yields are 20 to 30 kg/ha/d. It is interesting that supplemental feeding tables call for daily feeding rates of grains and pellets also at about 2 to 4% of the fish biomass, depending upon fish size and species.
In Israel, Schroeder (1979) has developed semiquantitative guidelines for the use of various manures. According to him, cow manure measured as DOM (dry organic matter) content should be added daily at a rate of 3–4% of the fish biomass of that day. On the same basis, chick manure at the rate of 2.5% and duck manure at the rate of 2%. From daily rates of manure production animal stocking rates can be calculated to provide (but not excede) 75–100 kg DOM/ha/day.
The Bureau of Commercial Fisheries recommends the feed at the rate of 3% of body weight/day, 6 or 7 days a week. According to the fish farming experiment station, Stuttgart, feeding should be done at the following rates at different temperatures:
|Rate of feeding||Temperature|
|% of body weight/day||°C or °F|
|3% of body weight/day||21°C–29°C (70° – 85°F)|
|2% " " "||15.5°C–21°C (60°–70°F)|
|1% " " "||7°C–15.5°C (45°–60°F)|
|No feed should be given||below 7°C (45°F)|
The chemical composition of excreta of different farm animals is shown in Table 2.
Table 2 : Chemical composition of excreta of different farm animals (%)
|Wastes||Dry matter||Ether extract||Crude protein||Crude fibre||Ash||Volatile organic matter|
Source: Sharma, Paul and Zariwala (1980).
China has a long history of intensive use of animal and domestic wastes for agriculture and a total annual organic fertilizer use (mainly from pigs) of about 1,689 million tonnes, equivalent to 8,320,000 tonne of nitrogen (N), 5,092,000 tonne of phosphorus (P) and 9,671,000 tonnes of potassium (K). Estimates of the annual tonnage of manure production/animal are as follows: Cow, 6.0; pig, 3.0; goat or sheep, 0.8 and Poultry, 0.05.
The amount of wastes excreted daily by an animal is directly proportional to its total live weight. Taiganides (1978) calculate the quantity of wastes produced by different animals given in Table 3.
Table 3 : Farm animal waste output and waste composition: TLW represents total live weight
|Parameter||Abbreviation||As a % of||Pork pigs||Laying hens||Feedlot beef||Feedlot sheep||Dairy cattle|
|Total wet wastes (feces and urine)||TWW||TLW/d||5.1||6.6||4.6||3.6||9.4|
|Total organic volatile solids||TVS||TS||82.4||72.8||82.8||84.7||80.3|
|Biochemical oxygen demand||BOD||TS||31.8||21.4||16.2||8.8||20.4|
|Chemical to biochemical oxygen demand ratio||COD:BOD||TVS||38.6||29.4||19.6||10.4||25.4|
Source: Taiganides, 1978.
Taiganides (1978) reported that animal manure contains the major inorganic nutrient components (N,P,K), in addition to such trace elements as Ca, Cu, Zn, Fe and Mg. The major nutrients come from the feeds fed to animals, of which 72 to 79% N, 61–87% P, and 82 to 92% K are recovered from the excreta. Urine comprising only about 40% by weight of the total daily waste excretion has higher N and K levels than faeces. Phosphorus is contained mainly in the faeces except for pigs which have high urine levels.
NPK Fertilizer use in aquaculture is well-known but the application rates vary with pond soil type and water quality; the quantity and fertilizer quality of animal wastes also vary according to species, size and age, feed and water intake, and environmental factors. Their availability is also influenced by the type of waste management practices. (Taiganides, 1978).
Nitrogen in animal wastes may be in the form of NH3, NH4, NO2, the levels of which vary considerably. Gaseous NH3 can easily be lost to the atmosphere, and handling can affect other losses of the various forms of N. In solid waste handling, losses of N may vary from 20% in deep pits to 55% in open feedlots, whereas in liquid handling N losses range from 25% for anaerobic systems to 80% under aerobic conditions (Taiganides, 1978).
In general, pig and poultry wastes contain higher P levels than cow manure. Phosphorus is bound to solids in most animal wastes and therefore handling losses are minimal.
Animals fed with high roughage rations will excrete more K than those fed on high concentrate rations. The vegetative parts of plant contain higher K levels than grains (Taiganides, 1978).
Based on the data in table(3), 2,500 laying hens (TLW 5,000 kg) will excrete 33,000 kg wastes/day comprising 495 kg N, 170 kg P and 145 kg K.
The animal manure is applied either fresh/untreated or after composting it in pits for some time. The application of fresh, untreated animal wastes to fish ponds is common in Asia and this practice has given high yields but excessive amounts can cause fish kills due to oxygen depletion in the water. Animal wastes delivered to fish ponds undergo decomposition through bacterial action and this process uses dissolved oxygen (DO), creating a Biochemical Oxygen Demand (BOD) which is often the greatest single factor determining the pond water DO. Schroeder and Hepher (1979) reported that such oxygen depletion could be predicted from BOD measurements in manured ponds. The BOD can also be estimated from the % dry matter content of manures. Manure is applied to ponds at daily rates of more than 1.5 t/ha under Israeli conditions. The 24-hr BOD at 30°C for various organic fertilizers and feeds used in Israeli ponds are given in table 4.
Table 4: The 24-hr Biochemical Oxygen Demand (BOD) for various fish foods and manures used for pond fertilization
|Material||% Dry matter||BODg-O2/kg/24 hr at 30°C|
|Pellets (25% protein, 10% fish meal)||90||140|
|Milled wheat and sorghum mixture (1:1)||90||96|
|Chicken manure||95||20 to 40|
|Field dried manure||36||10|
|Liquid cowshed manure||12.5||7|
|Liquid calf manure||9||5|
Levels of animal waste application to ponds as fertilizer.
Source: Schroeder, 1975.
These observations may be a usefull guideline for the management of manured ponds in the tropics to avoid dangerously low DO, particularly at night when no photosynthetic activity takes place. Poultry manure has higher biochemical oxygen demand (BOD), as compared to ruminant manure and reflects the higher food value both of the food eaten and manure produced. A high BOD implies rapid digestion and conversion to microorganisms upon introduction to the pond (Pullin and Shehadeh (1980).
The effectiveness of cow, chicken and pig manure as a direct fish feed has been tested in a variety of fish: Common Carp (Cyprinus carpio), (Shiloh and Viola (1973), Compos and Sampaio (1976), Kerns and Roelofs (1977), Tilapias (Sarotherodon mossambica)
(Stickney and Simmons 1977), channel catfish (Ictalurus punctatus), (Fowler and Lock 1974, Lu and Kevern 1975) and gold fish (Carassius auratus), (Lu and Kevern 1975). The usual approach in these experiments was to incorporate the dried manure into a standard feed pellet as a replacement for higher quality components in this manner, the first exposure of the fish to the manure was by direct consumption of the pellet. Experiments conducted in tanks or cages (the fish not having access to either the decay products of the un-eaten pellets or to fish faeces) showed that manures are poor substitutes for the components normally included in fish feed pellets. Consistently, with each increase in manure concentration in the pellet, there was a decrease in fish growth rates. Experiments conducted in open ponds, however, (the fish having access to the feed pellet decay products) gave results such that feeds containing as high as a 30% manure produced fish growth equal to the growth obtained with conventional fish feed pellets.
Metabolizable energy in cow and chicken manure is reported to range from 600–800 and from 900 to 1200 Kcal/kg for conventional feed pellets (Shiloh and Viola 1973) and 3,000 to 4,000 Kcal/kg for zooplankton (Yurkowski and Tabachnek, 1979).
In the United States, tilapia in manured ponds grew at 16.0 kg/ha/day compared to 25.8 kg/ha/day for ponds fed with commercial pellets. No significant difference was found between fish from the manured and pellet fed ponds. Although the yields from manured ponds are significantly lower than pellet-fed ponds, yet their profitability is higher where manure is available at a nominal cost. The cost of Tilapia production in pellet - fed ponds was $ 0.41/kg compared to a range of $ 0.02 to 0.21/kg for manured ponds (Collis and Smitherman 1978).