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MARES, J., JIRASEK, J., BARANEK, V., FIALA, J., KOPP, R.: Production effect of various feeds on two size classes of juvenile tench (Tinca tinca) under the conditions of intensive rearing. Acta univ. agric. et silvic. Mendel. Brun., 2007, LV, No. 1, pp. 111–116 The experimental rearing of tench (Tinca tinca) juveniles of two size classes with initial individual weight of 0.8 and 1.2 g was performed into fl ow-through aquaria connected to recirculation system during a period of 63 days. Three feeds (KARPICO Supreme 7 Ex, ASTA 2, L05/CH) with nutrient content of 37/8, 42/7 and 35/7 (% proteins/ fat) were used in the experiment. Achieved values of production indicators – feed conversion ratio (FCR) and specifi c growth rate (SGR) ranged from 1.84 to 4.15 and from 0.70 to 1.49 %.d–1, respectively in relationship to the size class and feed used. More favourable values were achieved with the bigger size class regardless to the diet used (FCR 1.84–3.53 and SGR 0.83–1.49 %.d–1) and the best results were achieved when using ASTA 2 feed (2.05 and 1.84 or more precisely 1.36 and 1.49%.d–1). juvenile tench, growth, feed conversion, specifi c growth rate, condition The increased requirements of European market cannot be satisfi ed by tench production in ponds and thus, possibilities for non-traditional breeding approaches to rearing of early and juvenile stages under controlled conditions of intensive aquaculture are searched for. Using a proper feeding strategy, the rearing of tench larval stages can be carried out successfully in recirculation facilities (WOLNICKI and KORWIN-KOSSAKOWSKI, 1993; WOLNICKI and GORNY, 1995; WOLNICKI et al., 2003). MARES et al. (2005) gained 97% survival rate when nursing the tench larvae till the age of 21 days upon commercial starter feeds under controlled conditions, which was found to be comparable to results gained with the live food. Results of the studies performed up-to-date showed a possibility to perform the intensive rearing of postlarval and juvenile stages of tench based on commercial feeding mixtures (QUIROS and ALVARIŇO, 1998; WOLNICKI and MYSZKOWSKI, 1998; RENNERT et al., 2003; WOLNICKI et al., 2003). When compared to juvenile stages of other cyprinids, the growth of tench fed with commercial feeds is extremely slow, even in case of addition of natural food (QUIROS and ALVARIŇO, 1998; MYSZKOWSKI et al., 2001; WOLNICKI et al., 2003, MARES et al., 2006; WOLNICKI et al., 2006). Another problem accompanying the intensive culture of juvenile tench utilizing commercial feeds is a frequent occurrence of morphological malformations, which might be associated with the quality of the diet used (KORWIN-KOSSAKOWSKI et al., 2004; WOLNICKI et al., 2006), with high feeding intensity (KAMLER et al., 2006) or with different growth performance (RENNERT et al., 2003). The absence of an appropriate feed is a factor limiting the nursing of larval and juvenile stages of tench under controlled conditions (QUIROS et al., 2003). The development and production of tench feed 112 J. Mares, J. Jirasek, V. Baranek, J. Fiala, R. Kopp prerequisits gaining knowledge on nutritional requirements of this species (JIRASEK and MARES, 2005). The goal of the experiment performed was to test the production effect of various feeds in juvenile tench of different size classes. MATERIAL AND METHODS The feeding test with tench juveniles of two size classes (0.83 g and 1.19 g) was performed from January 31 to April 4, 2005. The experiment was carried out in the experimental facility of the Department of Fishery and Hydrobiology of the Mendel University of Agriculture and Forestry in Brno, Czech Republic. Tench juveniles originated from artifi cial propagation (June 15, 2004) at Pohořelice Pond Aquaculture Co. and they were reared in the experimental facility under controlled conditions till the beginning of the test. The experimental goal was to test the production effi ciency of the following three feeds used for the size classes of tench under study: commercial extruded feed KARPICO Supreme 7 Ex (fa. Coppens, The Netherlands), produced commercially for common carp fry, feed ASTA 2 (Poland), a pilot-produced feed tested on various species and age classes of fi sh, and an experimental diet L05/CH of our own production with 0.5% Chlorella addition, based upon plant proteins and tested on other fi sh species as well. Results of chemical analyses of the diets used are given in Tab. I. The experiment was carried out in 6 fl ow-through aquaria (30 l volume with 15 cm height of water column) integrated into a recirculation system. Water temperature, pH and oxygen saturation of water (%) were measured daily. Mean water temperature during the experiment was 22.7 ± 1.3 °C, pH was 8.53 ± 0.05 and oxygen saturation was 104.7 ± 6.15 %. Content of N-NH4 + was lower than 0.1 mg.l–1 during the whole period and the content of N-NO2 – was less than 0.05 mg.l–1. I: Nutrient and energy content in the diets used (own analyses) Diet Dry matter (%) Protein (%) Fat (%) Ash (%) NFE (%) BE (kJ.kg–1) DE (kJ.kg–1) KARPICO 96.20 36.03 7.03 8.15 45.0