Response of juvenile tench (Tinca tinca L.) fed practical diets with different protein contents and substitution levels of fish meal by soybean meal Vanesa Garc  ıa, Jes  us Domingo Celada, Roc  ıo Gonz alez, Jos e Manuel Carral, Mar  ıa S aez-Royuela &  Alvaro Gonz alez Departamento de Producci on Animal, Facultad de Veterinaria, Universidad de Le on, Campus de Vegazana s/n, Le on 24071, Spain Correspondence: V Garc  ıa, Departamento de Producci on Animal, Facultad de Veterinaria, Universidad de Le on, Campus de Vegaz- ana s/n, 24071 Le on, Spain. E-mail: vgarm@unileon.es Abstract A basal practical diet for juvenile tench (Tinca tinca) was formulated and elaborated to test sev- eral protein contents and substitution possibilities of fish meal (FM) by soybean meal (SBM) in a 90- day trial with 5-month-old juveniles (30.54 mm TL, 0.30 g W). A factorial design included nine feeding treatments: three protein contents (50%, 40% or 30%) and three levels of replacement (0%, 25% or 45%) of FM protein by SBM protein. In addition, a commercial carp feed was used as reference. Final survival ranged from 98.2% to 99.4%. The 50% dietary protein with 0% or 25% replacement and 40% dietary protein with 25% replacement diets enabled higher growth (P < 0.05) and lower FCR (P < 0.05) than the rest of practical diets. Fish fed 50% dietary protein had similar growth than those fed carp feed (63.8% protein). Deformed fish averaged 1% for the practi- cal diets and 87.6% for the carp feed. The basal practical diet has showed to be feasible and levels of 40–50% dietary protein with 25% replacement of FM protein by SBM protein can be recom- mended for juvenile tench aged 5–8 months. Keywords: Tinca tinca, juveniles, practical diet, dietary protein, fish meal, soybean meal Introduction Tench (Tinca tinca L. 1758), a freshwater fish belonging to the family Cyprinidae, has a great potential for aquaculture (Steffens 1995; Kamler, Myszkowsky, Kami  nski, Korwin-Kossakowski & Wolnicki 2006; Wang, Min, Guan, Gong, Ren, Huang, Zheng, Zhang, Liu & Han 2006; Wolnicki, Myszkowski, Korwin-Kossakowski, Kami  nski & Stanny 2006). Originally occurring in the waters of Europe and Siberia, today tench occurs in the inland waters of all the continents (Freyhof & Kottelat 2008). In Europe, tench has a history of pond culture since the Middle Ages. However, the intensification of culture techniques has recently started. At present, tench is considered a promis- ing new species for intensive culture, which has drawn much attention from researchers and farmers. In natural habitats, tench are carnivorous, and very small amounts of plant material found in the alimentary tract have been swallowed incidentally along with live preys (Kennedy & Fitzmaurice 1970). Gut content analyses show that juveniles fed zooplankton and other small invertebrates (Pyka 1996, 1997). At present, juveniles are usually cultured in extensive or semi-extensive systems in earthen ponds, where control and man- agement of fish are difficult. Moreover, productions are unpredictable, recording frequently high mortality or slow growth. As consequence, the major obstacle for the increase of tench production is a deficit of young fish for stocking outdoor ponds or open waters (Wolnicki et al. 2006; Celada, Aguilera, Garc  ıa, Carral, S aez-Royuela, Gonz alez & Gonz alez 2009; Garc  ıa, Celada, Carral, S aez-Royuela, Gonz alez & Gonz alez 2010). For these reasons, special attention is being paid to find effective techniques for rearing juvenile tench © 2013 John Wiley & Sons Ltd 28 Aquaculture Research 2015, 46, 28–38 doi: 10.1111/are.12154