Effect of stocking density and protein/fat ratio of the diet on the growth of Dover sole (Solea solea) Giovanni Piccolo 1 , Stefania Marono 1 , Fulvia Bovera 1 , Ra¡aella Tudisco 1 , Gaetano Caricato 2 & Antonino Nizza 1 1 Department of Scienze Zootecniche e Ispezione degli Alimenti, University of Napoli Federico II,Via F. Delpino, Napoli, Italy 2 Department of Scienze delle Produzioni Animali, University of Basilicata, Campus di Macchia Romana, Potenza, Italy Correspondence: G Piccolo, Department of Scienze Zootecniche e Ispezione degli Alimenti, University of Napoli Federico II,Via F. Delpino, 1-80137 Napoli, Italy. E-mail: giovanni.piccolo@unina.it Abstract Two hundred and ¢fty soles (30 g initial weight) were randomly stocked in 12 tanks (recirculation system) at two di¡erent stocking densities (2.3 and 1.3 kg m  2 ) and fed on two di¡erent diets (50% and 54% of crude protein and 21% and18% of total lipid, respectively, for diets A and B) with triplicate tanks for treatment. The trial lasted for 300 days. Fish stocked at low density showed a signi¢cantly higher weight gain than the ¢sh reared at 2.3 kg m  2 density (94.1  7.4 vs. 78.9  8.2 g, Po0.01) with a speci¢c growth rate (SGR) of 0.46  0.11 and 0.43  0.16 ( Po0.01) respectively. Feed conversion ratio (FCR) was more favourable for lower density groups (2.50 vs. 2.64, Po0.01). Diet B led to a higher ¢nal weight (124.1 vs. 110.2 g, Po0.01) and a better feed utilization (FCR: 2.49 vs. 2.65, Po0.01). Except for the lipid content, which was higher in the low-density group (2.6% vs. 2.3%, Po0.05), proximate composition of sole’s muscle was not in£uenced by treat- ments. Dover sole reared at low stocking density showed higher monounsaturated fatty acid (35.27% vs. 34.40%, Po0.01) and lower saturated fatty acid (24.36 vs. 26.13%, Po0.01) contents, and lower atherogenic (0.67 vs. 0.75, Po0.01) and thrombogenic (0.28 vs. 0.32, Po0.01) indexes. Keywords: Dover sole, stocking density, protein/ fat ratio, growth performance, muscle composition Introduction Mediterranean marine aquaculture is mainly centred on two ¢sh species: European sea bass ( Dicentrarchus labrax ) and gilthead sea bream ( Sparus aurata ). The high increase in the production and the subsequent decline in the prices of these species during the last decade has brought about the need to ¢nd new ¢sh species suitable for farming. A number of studies indicate that Dover sole ( Solea solea ) is an interesting new species for marine aquaculture in Europe, as it is a highly valued species with a large market (Howell 1997; Bertotto, Francescon, Libertini, Poltronieri & Barbaro 2001; Tibaldi, Salvatori & Cenedese 2001; Zannella, Palazzi, Richard, Bozzato, Marangon & Salvano 2004; Lanari & D’Agaro 2005; Schram, Van der Heul, Kamstra & Verdegem 2006; Tibaldi, Salvatori, Cardinaletti, Mosconi & Calligaris 2007). Nevertheless, Dover sole is a relatively slow-growing species and requires a low stocking density, which may represent a problem for intensive aquaculture. Howell (1998) reported decreasing growth and increas- ing size variation for Dover sole when the stocking den- sity increased from 5% to 131% bottom coverage. Also, Schram et al . (2006) observed decreased weight gain with increasing stocking density for 40^74 g Dover sole stocked at increasing densities from 8% up to 195% bot- tom coverage. In this study, the optimal density corre- sponding to the highest productivity was 7.4 kg m  2 . Moreover, the nutritional requirements of this species are still not completely known. The aim of this study was to investigate the e¡ect of stocking density and di¡erent protein/energy ratio of the diet on the growth performance and quality char- acteristics of muscle of Dover sole. Material and methods Experimental conditions and ¢sh The trial was carried out at the Department of ‘Scienze Zootecniche e Ispezione degli alimenti’, in an indoor partially recirculating water system (total Aquaculture Research, 2008, 39, 1697^1704 doi: 10.1111/j.1365-2109.2008.02045.x r 2008 The Authors Journal Compilation r 2008 Blackwell Publishing Ltd 1697