Evaluation of the Dressing Percentage of 3-year-old Experimental Scaly Crossbreds of the Common Carp (Cyprinus carpio, Linnaeus 1758) in Relation to Sex

Buchtová H. , Z. Svobodová, M. Kocour , J . Vel í‰ek: Evaluation of the Dressing Percentage of 3-year-old Experimental Scaly Crossbreds of the Common Carp (Cyprinus carpio, Linnaeus 1758) in Relation to Sex. Acta Vet. Brno 2006, 75: 123-132. The aim of the present study was to compare dressing percentages, with relation to sex, of three bisexual groups of hybrid carp, i.e. Hungarian mirror carp and Northern mirror carp (M2 × M72), the hybrid line of Pfierov scaly carp and Northern mirror carp (PS × M72), the hybrid line of Pfierov scaly carp and Ropsha scaly carp (PS × ROP), and the pure line of Pfierov scaly carp (PS) in harvest size (K3). There were practically no differences in growth variables of male and female carp between the pure line PS carp and M2 × M72 and PS × ROP hybrids. Statistically significant differences in some variables between sexes were found in the scaly hybrid line PS × M72. Females in that group had significantly higher growth rates (TL and SL by 4.08% and 4.52%, respectively; p < 0.05), and their weight variables were also higher (FW, CW and FilletWabs by 11.37%, 13.70% and 14.83%, respectively; p < 0.05 and p < 0.01). The weight of gonads of male carp from all the groups studied was significantly higher (p < 0.01) than that of ovaries of female carp (or, rather, the GSI of male carp was higher). Carp, female, male, growth, weight, dressing percentage, gonadosomatic index The common carp (Cyprinus carpio L.) is an important freshwater fish raised for food in aquaculture all over the world. In the Czech Republic, carp production makes up about 85% of all freshwater fish farmed annually. Almost 50% of the carp produced is exported to the EU internal market under the Czech carp trademark (registered on 22 Oct. 2001 in the Czech Trademark Registry). In practice, high-yield carp that are the result of special breeding programmes are primarily used for commercial carp farming. A review of various technologies used in the study of different fish species has been published by Hulata (2001). Fish breeding in the Czech Republic is carried out on the facilities of the Czech Fishing Association under the supervision of the Research Institute of Fish Culture and Hydrobiology of the University of South Bohemia in âeské Budûjovice (VURHJU CB). In experiments performed on the facilities, various types of hybridization crossing (Gela and Linhart 2000; Linhart et al. 2002; Hartvich et al. 2003; Kocour et al. 2003; Gela et al. 2003; Kocour et al. 2005ab), genome manipulations (Flaj‰hans et al. 1993ab; Flaj‰hans 1997; Flaj‰hans and Linhart 2000), and, in some cases, selection methods are used to improve yield variables of fish. These methods of breeding are not generally successful in carp because their growth patterns are not affected by the additive effects of genes (Moav and Wohlfar th 1976). Neither have the genome manipulation techniques produced unequivocally positive results in carp growth rate experiments (Cherfas et al. 1994; Flaj‰hans et al. 1994). ACTA VET. BRNO 2006, 75: 123–132 Address for correspondence: MVDr. Hana Buchtová, Ph.D. University of Veterinary and Pharmaceutical Sciences Brno Department of Meat Hygiene and Technology Palackého 1-3 612 42 Brno, Czech Republic Phone: +420-541-562-742 Fax: +420-541-321-230 E-mail: [email protected] http://www.vfu.cz/acta-vet/actavet.htm Various types of hybrid (top, diallel, reproduction, combination) crossing, on the other hand, have produced some very good results, as evidenced by, e.g., growth rate tests performed regularly for newly bred hybrids of F1 generations and their parents throughout their life until they reach harvest maturity (Duda et al. 1999; Gela and Linhart 2000; Gela et al. 2003; Kocour et al. 2005a). Not even in these cases, however, heterosis will necessarily have a positive effect on the growth potential of the progeny of all the hybrids tested. In practical terms, the volume of freshwater fish production on a commercial farm will also be influenced by a number of other factors (e.g. the composition and density of fish stock, health and welfare of the fish, use of suitable feeding patterns and feeds with an optimum composition of nutrients, essential nutrients, minerals and vitamins, geographical location and quality of the environment). An increase in production can be achieved by purposefully farming only one of the sexes, which is particularly true about fish species characterized by a large degree of sexual dimorphism (Tinca tinca) (Flaj‰hans et al. 1993ab; Buchtová et al. 2003ab). In other fish species, the farming of only one of the sexes can be recommended only after a very thorough research (Goudie et al. 1994; Pongthana et al. 1999; Dan and Li t t le 2000; Nam et al. 2001; Kocour et al. 2005b). The aim of the present study was to compare dressing yields in four groups of carp: (1) Hungarian mirror carp and Northern mirror carp (M2 × M72), (2) pure line of Pfierov scaly carp (PS), (3) hybrid line of Pfierov scaly carp and Northern mirror carp (PS × M72), and (4) a hybrid line of Pfierov scaly carp and Ropsha scaly carp (PS × ROP) in harvest size (K3) and in relation to sex. The study is a part of a project of comprehensive assessment of carp hybrids where, besides production variables, also quality variables (basic chemical composition, spectrum of amino acids, spectrum of fatty acids) of edible parts (muscle tissue, hard and soft roe, hepatopancreas) will be investigated. Materials and Methods The performance test of scaly types of the common carp started in 2001 by the fish farming company Rybníkáfiství Pohofielice. In the experiments, the Pfierov scaly carp (PS) were used at the maternal position. These were crossed with male carp of other breeds (top crossing) namely the Pfierov scaly carp (PS) for the production of a pure line, and the Ropsha scaly carp (ROP) and the Northern mirror carp (M72). The mirror carp hybrid of the Hungarian and the Northern mirror carp (M2 × M72) were used as controls. The establishment of test populations and the test protocol were designed according to Linhart et al. (2002) and Kocour et al. (2005). In the first test year, fry was introduced to 6 fishponds (0.06 ha), and the stocking density was 20 000 fish per 0.06 ha. At an advanced fry stage (after 6 weeks), the carp were fished out, checked for weight and the stocking density was reduced to 1 600 fish/0.06 ha. Because natural diet was abundant, the fry were fed limited amounts of sieved wheat meal and, exceptionally, carp feed mixture pellets (KP1). The next growth and survival check was made at the end of the vegetation period before the carp were transferred to special wintering tanks (2001). From 2002 onward, the fish were kept in three ponds, namely the Antonín (2 700 carp/1.27 ha), Bohumír (3 400 carp/1.60 ha) and Jaroslav ponds (2 400 carp/1.13 ha). These ponds are supplied with water from the Nesyt pond. No fertilizers were used in the fishponds, and two-year old grass carp were introduced there (150 grass carp per pond) to control macrophytes. For additional feeding of the fish tested, uncrushed whole wheat was used. Checks of fish weight and survival checks were always made before and after wintering period. The performance assessment was made at the end of the 2003 vegetation period for K3 from all three fishponds (258 carp in total). A total of 15, 14 and 35 carp of each group were randomly selected from fishponds Antonín, Bohumír and Jaromír, respectively. The fish were processed in a standard manner (Gela and Linhart 2000) in the Mu‰ov Freshwater Fish Processing Plant of the Rybníkáfiství Pohofielice Comp. The dressing out was performed manually. The fish were scaled, gutted and filleted. Gonads were separated from the viscera. The head was cut off from the skeleton by a circular cut in front of the pectoral fin girdle so that the fin girdle remained at the body (Gela and Linhart 2000). Fillets were made with skin separating the flesh from spine and rib bones. In relation to sex (female vs. male carp), attention was paid to variables important from the breeding and the yield points of view. They include biometric variables, i.e. total length (TL), standard length (SL), carcass length (CL), head length (HL), body height (BH) and body width (BW), as well as weight variables, i.e. fish weight (FW), carcass weight (CW), fillets weight, remnant weight (spine and rib bones after filleting), head weight, fins weight, gonad weight (GW), viscera weight (including hepatopancreas without gonads), hepatopancreas weight, and waste 124