1318 degeneration (Hayes et al. 1975; Sturman 1988). In ﬁsh, the ability to biosynthesise taurine varies inter-speciﬁcally and throughout ontogenesis (Goto et al. 2001, 2003; Yokoyama et al. 2001; Kim et al. 2003, 2008), indicating that taurine may be essential for various ﬁsh species during some developmental stages. This seems to be the case for Japa- nese ﬂounder (Paralichthys olivaceus), which has been shown to have a low capacity for taurine biosynthesis, requiring dietary taurine for normal growth, development and feeding behaviour (Kim et al. 2005, 2008). Based on this, dietary taurine supplementation is recommended on a general basis for ﬂatﬁsh during ontogeny (Takeuchi 2001). Dietary taurine deﬁciencies may be particularly critical for ﬂatﬁsh during the larval stage. On one hand, taurine levels remain stable during the yolk-sac and mouth opening stages of ﬂatﬁsh development, suggesting that taurine is incorpo- rated into the free AA pool of the egg before spawning (Rønnestad and Fyhn 1993; Rønnestad et al. 1993). Like in the mammalian embryo, these ﬁndings suggest that taurine may have a signiﬁcant physiological importance for the development of ﬁsh embryo (Sturman 1993). Furthermore, the prey of ﬂatﬁsh larvae in the natural environment (e.g. copepods) contain high taurine levels (Conceic¸a˜o et al. 1997; van der Meeren et al. 2008), and high taurine levels in live food were suggested to result in higher growth rates of turbot (Scophthalmus maximus) larvae (Conceic¸a˜o et al. 1997). Nevertheless, although dietary taurine supplementation is likely to be beneﬁcial for ﬂatﬁsh larvae, there is no infor- mation available on the mechanisms involved in taurine absorption in the digestive tract and the bioavailability of dietary taurine in the early developmental stages. The research on intestinal taurine transport in vertebrates mainly targets the high-afﬁnity, low-capacity sodium/ chloride-dependent taurine transporter (TauT; SLC6A6) (O´ Flaherty et al. 1997). This transporter functions as an active transport system that carries taurine against a con- centration gradient, driven by transmembrane sodium and chloride gradients and membrane potentials. TauT has been cloned and characterised in a range of species and tissues, including Madin–Darby canine kidney cells (Uchida et al. 1992), porcine renal proximal tubule cells (Jones et al. 1995), mouse (Liu et al. 1992) and human (Jhiang et al. 1993; Ramamoorthy et al. 1994). In ﬁsh, only a few studies have aimed to characterise TauT (Takeuchi et al. 2000; Zarate and Bradley 2007; Kozlowski et al. 2008; Chow et al. 2009), and to our knowledge no work has analysed TauT expression in ﬂatﬁsh species or during ﬁsh larval stages. In fact, up to now few works have been done on the molecular characterisation of transporters in teleosts in general (e.g. Verri et al. 2003) and in larvae (Amberg et al. 2008). In mammals, several AA transporters appear at dif- ferent times during ontogenesis (Buddington and Diamond 1989). Although the ontogeny of ﬁsh larvae is not 123 W. Pinto et al. comparable to foetal mammals, it remains to be explored if this also holds true for teleosts. It has been shown that ﬁsh larvae do not have a fully developed digestive system at the onset of exogenous feeding and the digestive/absorption capacities increase along with development (Conceic¸a˜o et al. 2007; Rønnestad et al. 2007). Therefore, since ﬂatﬁsh may require dietary taurine supplementation during the early developmental stages, it is important to determine the functionality of TauT during ontogenesis. This work aimed to characterise TauT expression during the ontogeny of Senegalese sole (Solea senegalensis), a ﬂatﬁsh species with increasing importance for the South- Eastern European aquaculture (Imsland et al. 2003; Con- ceic¸a˜o et al. 2007) and that seems to require dietary taurine supplementation during the early life stages (Pinto et al. 2010). For this purpose, TauT was cloned from Senegalese sole cDNA and its expression was determined by real time quantitative PCR (qPCR) from ﬁrst feeding larvae until juvenile stages of development. Materials and methods Fish rearing Senegalese sole (S. senegalensis) larvae were reared at UAlg (Faro, Portugal) according to standard procedures until 30 days after hatching (DAH) (Dinis et al. 1999). Larvae were initially reared in 100 L conical cylindrical sand- coloured tanks at a density of 80 larvae L-1. At 16 DAH, benthonic Senegalese sole were transferred to 21 L sand- coloured ﬁbreglass raceways (0.21 m2; 10 cm water depth; initial larval density of 3,000 individuals m-2). Light/dark cycles of 12:12 h were used throughout the experiment. Water temperature (21.0 ± 1.5 C; mean ± SD), oxygen saturation level (96.1 ± 4.6%) and salinity (33.8 ± 2.6 g L-1) were measured on a daily basis. The Senegalese sole larvae were fed rotifers and Artemia enriched with commercial products according to standard rearing proce- dures (Dinis et al. 1999). Juvenile Senegalese sole were obtained from a different batch of larvae reared at CCMAR (Faro, Portugal) facilities in a ﬂat-bottom sand-coloured ﬁbreglass tank (2.40 m length; 1 m width; 30 cm depth) at a density of 8 kg m-2. Water supply was provided by a partial-recirculated water system (temperature 21 ± 1 C; salinity 36 g L-1). Fish were fed to satiety with a commercial diet (Dourasoja Balance, Sorgal, S.A.) and fasted for 24 h before sampling. Fish sampling Senegalese sole larvae were sampled for total length (TL), dry weight (DW) and metamorphosis pattern analysis at