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There is an increasing interest in defining optimal conditions to rear salmon to market size in recirculating aquaculture systems (RAS). Salinity however, as a parameter that can be potentially manipulated, has been poorly studied. To address this knowledge gap, we reared coho (Oncorhynchus kisutch Walbaum, 1792) and Atlantic (Salmo salar Linnaeus, 1758) salmon from smolt to market size over ~460 days at five different salinities (0, 5, 10, 20 and 30 ppt) and examined their growth performance. We found that both species reared at intermediate salinities (5-10 ppt) started to show significantly larger body mass than fish reared either in freshwater or full-strength seawater at around day 250-300. These growth-enhancing effects were maintained until day 460. The higher growth in Atlantic salmon at intermediate salinities was associated with reduced economic feed conversion ratio, but this was not observed in coho salmon. The all-female coho salmon showed no incidence of sexual maturation and negligible cataract formation, while the mixed-sex Atlantic salmon showed high levels of sexual maturation (up to 50%) and presence of cataracts (up to 60%). Our results indicate that all-female coho salmon may be better suited to RAS than Atlantic salmon in some aspects. However, in both species, long-term rearing at intermediate salinities improves growth in RAS.

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