INVESTIGATION OF QUANTITY AND CHEMICAL CHARACTERISTICS OF BIGHEAD CARP (Aristichthys nobilis) BY-PRODUCTS

Bighead carp (Aristichthys nobilis) successfully grow in polyculture with carp, feeding on plankton. It has good quality of meat for both consumption and industrial processing. Th e quantity of by-products obtained during primary processing of bighead carp and chemical characteristics of internal organs were investigated in this paper. Th e total average weight of by-products was 760.45 g (42.31%) in relation to live body weight, whichwas cca 1797.5 g. Th e by-product contributing to the largest quantity to total live body weight was the head with 529.39 g (29.45% of live bodyweight), followed by complete internal organs and tail and fi ns, which weighed 137.67 g (7.66%) and 68.82 g (3.83%), respectively Chemical composition of internal organs of bighead carp was mostly water (60.99%), following by crude fats and crude proteins (21.20% and 10.61%, respectively). The low collagen content (15.25% of total crude protein) indicates the high nutritional quality of protein content from internal organs. Nitrogenous complexes from the internal organs were predominantly proteins. Digestible nitrogen was approximately equal to total nitrogen (92.04%), indicating that all proteins of the internal organs had high biological value. Based on the results obtained, it can be concluded that bighead carp internal organs could be important sources of proteins and fats, and thus, could be used in Serbia as a raw material for feed and technical fat production.


INTRODUCTION
Th e aquaculture industry has grown rapidly over the last decade. Likewise, mariculture is expanding worldwide thereby increasing the demand for feed ingredients to support production (FAO, 2014). Th e rapidly growing sector directly depends on the aquafeed industry, which in turn largely depends on fi sh meal as its primary protein source.
Over the last decade, the global supply of fi sh meal has been limited, and meeting the demands of a growing industry has become challenging. In addition, fi sh meal proteins experience periodic fl uctuations in pricing and availability (Tacon et al., 2008).
Freshwater fi sh contain high levels of PUFA, which makes them very important in human nutrition (Vladau et al., 2008). Since there are a number of biochemical interactions between the n-6 and n-3 series fatty acid, a balanced ratio between these fatty acids in the food is important for the normal functioning of the body in humans, as well as in animals (Đorđević et al., 2009). Consumption of fi sh meat is increasing, due to its high content of polyunsaturated fatty acids (PUFA), amino acids and lipid soluble vitamins which are important ingredients for human health. According to the latest data from FAO (Ćirković et al., 2012) the Republic of Serbia is a country where the average consumption of fi sh is 5-10 kg per capita per year, which is signifi cantly below the European and global consumption (Ćirković et al., 2011).
Common carp is economically the most signifi cant farmed fi sh species on the fi sh farms in Serbia (FAO, 2012), and the cyprinids are the most common species in the total world production of freshwater fi shes (71.9%, 24.2 million tons in 2010) (Ćirković et al., 2012). Bighead carp (as well as grass carp) was imported in our country as a regulator of hydro vegetation. It feeds on higher underwater plants and its meat is of good quality (Vujković et al., 1993).
Manufacturing and development of fi sh products could increase the off er and contribute to better sale of fi sh, not only in traditional fi sh markets, but also in retail stores and supermarkets. Technological processes, preservation and storage of fi sh meat diff er from those characteristic for mammalian meat (Okanović et al., 2015). For proper manufacturing of fi sh products, knowledge about chemical composition and characteristics of raw fi sh meat is of highest importance in order to apply the most appropriate technology procedures adjusted to individual fi sh species.
Fish processing and development of new fi sh products can provide novel sale of fi sh, not only in traditional fi sh markets, but also in all other consumer goods stores . Th e demands of modern markets are increas-ingly directed towards processed fi sh, especially fi llets. Larger quantities of edible and non-edible by-products are obtained in industrial conditions of primary fi sh processing (Ristić et al., 2002).
Fish yield, expressed as the ratio of the weight of the carcass without the head, scales, fi ns and internal organs and whole fi sh mass, are essential parameters for all technological operations related to fi sh processing, since the economy of production is directly dependent on it .
On the basis of some previous research, it is well-established that byproducts of bighead carp processing contain valuable nutrients, which may be sources for the food, pharmaceutical and feed industry (Ristić et al., 1992). In order to obtain more complete perception of the quality of animal by-product, it is necessary, in addition to knowledge of basic chemical composition, to obtain complete information on the quality of the most important nutritional components -proteins. However, the high crude protein content of some raw materials does not guarantee its high usability, ie. protein digestibility (Ristić et al., 2011).
Inedible by-products obtained during bighead carp slaughter belonging to the third category of by-products (Regulation EC, 2009) are important sources of proteins and fats that represent convenient raw materials for processing into proteinaceous feeds for swine and pets.
Due to the increasing industrial grass carp processing and need for complex utilization of obtained by-products, the aim of this research was to investigate the quantity of by-products and nutritive value of internal organs.

MATERIALS AND METHODS
Th e quantity of by-products and quality of internal organs were monitored during fi sh harvesting and processing of bighead carp from fi sh ponds in Vojvodina in industrial conditions. Bighead carp from fi sh ponds Ečka were delivered live from fi sh farm to a manufacturing plant where they were immediately sacrifi ced. Mean values of bighead carp mass were approximately 1800 g. Scales, gills and viscera, heads (fl at transverse incision just behind the gill arch) and the fi ns were removed with a knife (Photograph 1). Th e following values were measured: weight of fi sh before the cutting, meat head, mass of the tail and fi ns and mass of total internal organs. Th e total internal organs are not separated because in industrial conditions it is standard procedure. To the purpose of appropriate interpretation of the obtained data they were statistically evaluated (Stat Offi ce RS, 2014) using calculations of arithmetic mean (X̄), standard deviation (SD) and coeffi cient of variation (CV).

RESULTS AND DISCUSSION
Th e quantities of by-products obtained from bighead carp processing are presented in Table 1. Aft er cutting-off the head, tail and fi ns and removal of complete internal organs, average carcass weight was 1013.55 g (56.39%) of total live body weight. Routine removal of skin, bones, spinal and rib carcass produced an average fi llet weight of 817.29 g (45.47%) and the bones with the remains of the corresponding meat. Total average weight of by-products was 760.45 g (42.31%) in relation to livebody weight which was cca 1797.5 g. Th e by-product with the largest proportion of total live body weight was the head with 529.39 g (29.45%), followed by the whole internal organs and the tails and fi ns which had weight 137.67 g (7.66%) and 68.82 g (3.83%), respectively.
Th e head weight largely depends on the processing method (straight or round cut behind the gills). In the research of Tumbas and Petrović (1978), the head obtained with a circular cut was 11% of the live body weight. Th e weight of tail and fi ns 99.15 g (5.11%) was smaller than the weight of heads. Total internal organs weighed 143.77 g (12.22%). According to Ristić et al. (1992) bighead carp by-products percentages ranged from head 19.79%, tail and fi ns 3.09% and total internal organs 9.47%. Results of the chemical composition of the internal organs are shown in Table 2.
Basic chemical composition showed that this raw material, apart from water (60.99%), contained mostly crude fat (21.20%) and then crude proteins (10.61%). Th e low proportion of collagen (15.25%) in the total crude protein indicates the high nutritional quality of the protein.
In the research of Ljubojević et al. (2013), the fat content in the bighead carp ranged from 2.3 to 16.8%, while the protein content was less variable and generally was in the range from 14 to 18% As seen in Table 2, nitrogen complex of bighead carp internal organs was composed mostly of protein. Th e high digestibility of the protein (92.04%) indicates the high biological value of proteins of the internal organs. In the research of Ristić et al. (2002) it has been shown that a set of internal organs of bighead carp contained a higher share of fat (21.20%) as well as protein with good digestibility (92.04%).

CONCLUSIONS
Based on the results obtained in this study it is possible to conclude the following: -Aft er cutting-off the head, tail and fi ns and removal of complete internal organs the average carcass weight was 1013.55 g (56.39%) of the live weight. -Th e total average weight of by-products was 760.45 g or 42.31% in relation to live body weight (cca 1797.5 g). -Th e head had the largest proportion of weight in relation to live weight, being 529.39 g (29.45%) of live weight. Weights of tail and fi ns were much smaller, being 68.82 g (3.83%). Th e total internal organs weighed 137.67 g (7.66%). -Chemical analyses revealed that the internal organs, apart from water, contained signifi cant amounts of crude fat (21.20%) and protein (10.61) making them suitable for feed processing. -Th e amount of digestible nitrogen in the internal organs was approximately equal to total nitrogen (92.04%), indicating that all proteins from the internal organs have high biological value. -Inedible internal organs obtained during bighead carp slaughtering could be an important source of nutritive components and could be used as raw material for processing into feeds for use in animal nutrition.