Effects of dietary phytosterols and soy saponins on growth, feed utilization efficiency and intestinal integrity of gilthead sea bream (Sparus aurata) juveniles A. Couto a,b, ⁎, T.M. Kortner c , M. Penn c , A.M. Bakke c , Å. Krogdahl c , A. Oliva-Teles a,b a Departamento de Biologia, Faculdade de Ciências da Universidade do Porto, 4169-007 Porto, Portugal b CIIMAR — Centro Interdisciplinar de Investigação Marinha e Ambiental, 4050-123 Porto, Portugal c Department of Basic Sciences and Aquatic Medicine, Norwegian University of Life Sciences, P.O. Box 8146 Dep., N-0033 Oslo, Norway abstract article info Article history: Received 22 January 2014 Received in revised form 14 April 2014 Accepted 1 May 2014 Available online 20 May 2014 Keywords: Antinutrients Gilthead sea bream Saponins Phytosterols Soya The use of plant ingredients in aquafeeds for piscivorous fish species is a reality that exposes fish to a number of antinutritional factors present in plants. The present study is the first to evaluate the effect of two purified antinutrients, saponins and phytosterols, in sea bream juveniles. For that purpose, seven diets were formulated: a control diet (fishmeal and fish oil based) and six experimental diets containing low (1 g kg −1 , SapL) or high (2 g kg −1 , SapH) levels of purified soya saponins, low (5 g kg −1 , PhytL) or high (10 g kg −1 , PhytH) levels of purified phytosterols or a combination of 1 g kg −1 saponins + 5 g kg −1 phytosterols (SapPhytL) or 2 g kg −1 saponins + 10 g kg −1 phytosterols (SapPhytH). Fish were fed for 48 days in order to evaluate growth perfor- mance, feed utilization, plasma cholesterol, and gut health as assessed by histomorphological evaluation and gene expression profiling of immune and functional markers. Fish fed the diets PhytH, SapPhytL and SapPhytH showed better feed utilization and PhytH and SapPhytH showed higher protein utilization than the other groups, although this was not reflected in improved growth performance. Histomorphological analysis of the distal intes- tine revealed increased variation in supranuclear vacuole sizes after 48 days of feeding diets SapH, SapPhytL and SapPhytH and increased number of intraepithelial leukocytes in response to all dietary treatments except SapL and SapPhytL. Although juvenile sea bream growth was not affected by dietary inclusion of saponins and phytos- terols, the results indicated some disturbances of the intestinal mucosal structure that could compromise function and/or protection from potential dietary antigens or opportunistic pathogens. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The aquaculture industry strives to improve its sustainability by shifting towards lower use of finite marine-harvested resources. During the past decade, a great deal of research has focused on reducing fish meal (FM) and fish oil (FO) in aquaculture feeds by introducing plant feedstuffs, which are now commonly used by the aquafeed industry (Rust et al., 2011). As awareness towards the importance of nutrition– health relationship gains ground, pressure to develop sustainable aquafeeds capable of eliciting proper growth while maintaining fish health and welfare increases (Kiron, 2012; Oliva-Teles, 2012). Partial replacement of FM and FO by plant sources has been shown to be feasi- ble in several studies with gilthead sea bream (Sparus aurata) without affecting the zootechnical performance of the animals (Benedito-Palos et al., 2007; Benedito-Palos et al., 2008; Bonaldo et al., 2008; Dias et al., 2009; Gomez-Requeni et al., 2004; Kokou et al., 2012; Silva et al., 2010; Sitja-Bobadilla et al., 2005). Recently a study by Watson et al. (2013) reported the successful use of a 100% plant diet for sea bream without affecting growth performance; however, no information on fish intestinal physiology, histomorphology or immune parameters was provided. This may be significant because other studies with sea bream fed plant feedstuff-rich diets have demonstrated intestinal inflammation (Bonaldo et al., 2008) or impaired immune response (Kokou et al., 2012; Montero et al., 2010; Sitja-Bobadilla et al., 2005) without compromising fish growth. Most plant-derived feedstuffs contain antinutritional factors, which are defined as substances that by themselves or through their metabolic products interfere with feed intake, nutrient digestibility, intestinal physiology, metabolism, growth, and/or health of the animal (Francis et al., 2001; Gatlin et al., 2007; Krogdahl et al., 2010). The increasing use of plant feedstuffs in diets can expose fish to cumulative effects of antinutrients, which may result in a late manifestation of decreased Aquaculture 432 (2014) 295–303 ⁎ Corresponding author at: Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal. Tel.: +351 22 040 2736; fax: +351 22 040 2709. E-mail address: acouto@fc.up.pt (A. Couto). http://dx.doi.org/10.1016/j.aquaculture.2014.05.009 0044-8486/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online