Until recently compound feed was mainly used to rear common carp fry, but in the past two decades cereals in the diet of common carp grown to market size have also been substituted with compound feed. In contrast to feeding fish with cereals in the form of grains, when preparing compound feed cereal grains are ground up and enriched with proteins of plant and animal origin, by-products of the food industry, as well as with vitamins and minerals. The composition varies, depending on the region where the crops are grown. To prevent decomposition in the water, preliminarily ground up components of the mixture are bonded into pellets of various shapes and sizes, depending on the age category of the fish. The process of preparing industrial feed for aquaculture is based on pelleting and extrusion technologies.
Effect of using different feeds on common carp production
The production of common carp in a semi-intensive system depends on: characteristics of the pond biotope (depth, turbidity, area); quality and quantity of the water used to fill and refresh ponds; fish quality and stocking density; agrotechnical and preventive measures used in the process of preparing ponds for stocking and during the production cycle; climatic conditions; the quantity and development of natural food; and a type of supplemental feed. When feeding with cereal grains, structural components are mainly obtained from natural food (primarily zooplankton and the bottom fauna), while energy needs are satisfied for the most part by supplemental carbohydrates. In such production, the increase in the weight of the fish depends primarily on natural food, especially during periods of higher abundance.
Under temperate conditions at the beginning of summer, the biomass of zooplankton and the bottom fauna decreases due to their natural variability. At that point, growing fry cannot meet their increased demand for proteins. The attempt to compensate for the deficiency of protein from natural food by feeding with cereal grains results in a daily weight gain that is significantly smaller than during the spring, when natural food is well developed. This poses the question of how to ensure enough protein during the summer, when the water temperature is most favourable for common carp growth, to maintain the daily percentage increase of growth on a level similar to that achieved in spring. One way is by providing the common carp with supplemental (compound) feed with a greater percentage of protein than that contained in cereal grains.
The type and amount of feed and the time and frequency of feeding improve the growth rate of farmed common carp. Quantity of common carp that can be obtained in semi-intensive production based on cereal grains vary from 500 kg/ha to more than 1,500 kg/ha. Under conditions of good development of natural food in combination with cereal grains and frequent feeding throughout the day, the indicated level of production can be even higher (more than 2,000 kg/ha). The yields under conditions of using compound feed in a semi-intensive system vary from 1,200 to 3,000 kg/ha, depending on the aforementioned factors. Owing to the better physical and chemical properties of extruded feed, its use results in higher production than that obtained in common carp farming based on pelleted feed. Thus, use of extruded feed can give a yield that is on the upper limit of the range indicated for compound feed under conditions of optimal water temperatures during farming of common carp. In addition to the direct influence of a protein content higher than in cereal grains, use of compound feed also indirectly influences common carp growth in pond systems. Compound feed contains rapidly degrading substances that partially decompose as uneaten food but are also eliminated undigested from the fish or are excreted in the form of metabolic products, which contributes to the continual presence of small amounts of nutrients (nitrogen and phosphorus) and carbon dioxide in the water. Their presence stimulates primary and secondary production in the pond. As a result, the presence of natural food is greater when the fish are fed supplemental protein feed (compound feed) than when fed with cereal grains. Since nutrients are dissolved in small amounts and in continuity from supplemental protein feeds, the negative consequences on the oxygen balance are also reduced, as well as the possibility of development of algal blooms.
Effect of using different feeds on the quality of common carp flesh
The increasing demand and consumption of fish from aquaculture pose certain requirements regarding its quality and nutritive properties. In the past decades, studies of fish feed and improvement of feed quality have contributed to the development of aquaculture and led to an increase in the nutritive value of farmed fish. The chemical composition of fish flesh is affected by numerous factors: genetic parameters, fish size, sexual maturity and life cycle phase, microclimate, water quality, quality and amount of food and the time and frequency of feeding. Nutrition, but primarily feed quality, is one of the most important factors affecting the chemical composition of fish. The percentage of protein is higher, while percentage of lipids is smaller in flesh of common carp fed compound feed compared to common carp fed cereal grains. Fatty acid composition is of special significance for the quality of fish flesh. Producing fish with a better ratio of omega 3 and 6 fatty acids is very important for aquaculture. This is especially important considering that the resources of marine fish are limited. Comparative analysis of the influence exerted by three types of feed (cereal grains, pelleted feed and extruded feed) on the fatty acid composition of common carp flesh showed that use of extruded feed provided the best results.
Effect of using different feeds on the water quality in the pond
The use of protein supplemental feed in semi-intensive fish farming opens the question of sustainability, especially the problem of protection of water quality. Regardless of whether cereal grains or compound feeds are used, part of the feed almost always remains uneaten. The bulk of uneaten food falls to the bottom and undergoes processes of decomposition to inorganic matter. Uneaten food, undigested remains and metabolic products of digested food are retained in the water and influence the fishpond ecosystem. Additionally, these substances also enter the food chain and, in this way, exert indirect influence on the physical, chemical and biological characteristics of the water. Comparison of water quality in carp ponds under conditions of using various types of feed indicates that there are no significant differences. Although it was expected that feed with a higher percentage of proteins would cause disturbances in the aquatic ecosystem, their continual incorporation into the cycling of matter in the water contributes to maintenance of ecological equilibrium and even indirectly promotes growth of the common carp.
Effect of using different feeds on the economy in carp semi-intensive carp production
Economy in aquaculture, as in all other animal production areas, is determined by production inputs and prices of the final product. Feed is one of the most important inputs in semi-intensive production, and the choice of the supplemental feed influences profitability. However, the price of the added feed cannot be considered as the main factor for the decision. Apparently, the choice of the feed is not the universal decisive factor in attaining profitable production. Some of the factors that could be decisive are: stocking density; quantity of fish produced per hectare of the pond; duration of the production process from fertilised eggs to market size; as well as the size of the ma carp. Not to be neglected are inputs that vary from country to country such as: fees for the water used for fish farm supply, prices for fuel or electric energy, costs for manpower, the level of protection from predatory birds and mammals; and the existence or absence of compensation for such losses. In view of the above it is clear that a general conclusion which is the most profitable way between cereal grains and compound feed to culture common carp cannot be derived. Such a recommendation could be given only for a single farm, for a country or a group of countries with similar aquaculture technologies, input prices and consumable carp prices.
Comparative analysis of using cereal grains and compound feeds in semi-intensive carp pond aquaculture indicates that priority should be given to common carp farming based on the use of compound feed as opposed to feeding with cereal grains. When it comes to different processing technologies for compound feeds, due to improved physical and chemical properties, use of supplemental extruded feed results in higher production per unit area compared to the use of supplemental pelleted feed.
Acknowledgments: This text is part of the published scientific paper entitled “Comparative analysis of using cereal grains and compound feed in semi-intensive common carp pond production” in Aquaculture International (2016) 24:1699–1723. Thanks to
my colleagues Marko Stankovic, Božidar Raškovic, Božidar Raškovic, Zorka Dulic, Ivana Živic and Vesna Poleksic, who were coauthors.
Prof. Dr. Zoran Markovic Faculty of Agriculture University of Belgrade Serbia