Comparative seawater performance and deformity prevalence in out-of-season diploid and triploid Atlantic salmon (Salmo salar) post-smolts E. Leclercq a , J.F. Taylor a , D. Fison a , P.G. Fjelldal b , M. Diez-Padrisa a , T. Hansen b , H. Migaud a, ⁎ a Institute of Aquaculture, University of Stirling, Stirling, Scotland, UK b Institute of Marine Research, Matre Research Station, Norway abstract article info Article history: Received 27 July 2010 Received in revised form 21 September 2010 Accepted 21 September 2010 Available online 29 September 2010 Keywords: Atlantic salmon Triploid Growth Deformity Vertebrae Cataract Family The use of sterile triploid stock in the Atlantic salmon (Salmo salar, L) farming industry is the only commercially available means to prevent the ecological impact of domesticated escapees. This study compared the seawater (SW) performance and deformity prevalence of diploid and triploid post-smolts from 2 full-sib families produced out-of-season. Triploids completed smoltification 4 weeks earlier and at a significantly higher body-weight. Growth and survival in SW were not significantly affected by ploidy. The incidence of external deformities, dominated by jaw malformation, was ~ 12% in triploids and below 5% in diploids. Vertebral deformities were more prevalent in the fastest growing triploid family only. Heart morphometry differed between ploidies which may relate to a higher cardiac workload in triploids. No clear alteration of the gill apparatus was detected. The most significant detrimental effect of triploidy was on the rate and severity of cataract that were observed from August onward (50% and 92% of diploids and triploids respectively affected after 1-year in SW). At that time, cataracts were diagnosed by histological examinations as irreversible with a probable osmotic origin which could arise from factors such as water quality, nutritional deficiencies or thermal variations. This study warrants further research aiming at adapting rearing practices to the needs of triploid stocks as to improve their performance and welfare. Crown Copyright © 2010 Published by Elsevier Inc. All rights reserved. 1. Introduction The increase in the global volume of farmed Atlantic salmon, Salmo salar, has given rise to increasing public and scientific awareness over the impact of farmed stocks on the integrity of wild populations (Glover et al., 2009). In the North Atlantic, an estimated two-million Atlantic salmon escape annually (McGinnity et al., 2003) and circa 1.9 million escapees were reported in Scotland alone between 2002 and 2008 with the vast majority on the west coast (Marine Scotland, 2010). Due to decades of domestication and selective breeding for economically driven traits (Gjøen and Bentsen, 1997), commercial strains of Atlantic salmon have a reduced genetic variation (Skaala et al., 2005), but are capable of survival, dispersion, homing and successful spawning upon escape (Lura and Sægrov, 1991; Webb et al., 1991, 1993; Hansen et al., 1993; Hansen, 1996; Hansen and Youngson, 2010). Interbreeding between wild and farmed strains could therefore reduce the fitness of the wild stock through genetic introgression (Crozier, 1993; McGinnity et al., 2003; Skaala et al., 2006; Castillo et al., 2008; Roberge et al., 2008). By providing genetic and reproductive containment, sterilization is the only reliable means to prevent such interbreeding and the propagation of non-native salmon (Fleming et al., 1996; Piferrer et al., 2009). Triploidization of newly fertilised eggs by hydrostatic pressure shock is an effective and well established protocol in Atlantic salmon to induce sterility (Benfey and Sutterlin, 1984; McGeachy et al., 1995; Benfey, 2001; Piferrer et al., 2009). For the on-grower, a sterile population could eliminate sexual maturation with its negative impact on growth, health, welfare and overall value of the stock (Kadri et al., 1996; St-Hilaire et al., 1998; Leclercq et al., 2010; Taranger et al., 2010). Despite the potential benefits, the sterilization of Atlantic salmon is seldom applied commer- cially unlike in other salmonids such as rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis) (Piferrer et al., 2009). Only the Australian industry has adopted this strategy (Sadler et al., 2000; Sadler et al., 2001; Lijalad and Powell, 2009). The main explanation for the lack of commercial implementation is the reduced culture performance of triploid stocks observed in previous studies and commercial trialing over the last two decades as well as consumer perception (Benfey, 2001; Oppedal et al., 2003). The reduced performance documented in triploids could result from their larger cell volume and reduced cell number suggesting a reduced cell surface area to volume ratio and a lower capacity for cellular metabolic exchange (Suresh and Sheehan, 1998; Hyndman et al., 2003; Benfey and Bennett, 2009). This could also affect the physiology and especially organ development and morphometry of triploids but evidences remain scarce to date. Variations in muscle fiber population and morphometry were documented in Comparative Biochemistry and Physiology, Part A 158 (2011) 116–125 ⁎ Corresponding author. Tel.: +44 1786 467886; fax: + 44 1768 472133. E-mail address: hm7@stir.ac.uk (H. Migaud). 1095-6433/$ – see front matter. Crown Copyright © 2010 Published by Elsevier Inc. All rights reserved. doi:10.1016/j.cbpa.2010.09.018 Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part A journal homepage: www.elsevier.com/locate/cbpa