Abstract
Atlantic salmon farming operates with high production intensities where skin integrity is recognized as a central factor and indicator for animal health and welfare. In the described trial, the skin development and its immune status in healthy Atlantic salmon reared in two different systems, a traditional open net-pen system and a semi-closed containment system, were investigated. Freshwater smolts were compared to post-smolts after 1 and 4 months in seawater. Growth performance, when adjusted for temperature, was equal between the systems. Skin analyses, including epidermis and dermis, showed that thickness and mucus cell numbers increased in pace with the growth and time post seawater transfer (PST). Gene expression changes suggested similar processes with development of connective tissue, formation of extracellular matrix and augmented cutaneous secretion, changes in mucus protein composition and overall increased immune activity related to gradually enforced protection against pathogens. Results suggest a gradual morphological development in skin with a delayed recovery of immune functions PST. It is possible that Atlantic salmon could experience increased susceptibility to infectious agents and risk of diseases during the first post-smolt period.
Highlights
Success and sustainable growth of the commercial Atlantic salmon (Salmo salar) aquaculture depend principally on fish health and welfare
Fish weight, cumulated mortality, farming and environmental parameters for semi-closed containment systems (S-CCS) and the open net-pen systems are illustrated in Supplementary Fig. S1
The mean body weight estimates (Table 1) from production data was 109 and 113 g when transferred to the open net-pen and S-CCS, respectively
Summary
Success and sustainable growth of the commercial Atlantic salmon (Salmo salar) aquaculture depend principally on fish health and welfare. Development of semi-closed containment systems (S-CCS) at sea is a promising strategy aiming at further expansion of the Atlantic salmon production in Norway[1] These systems are developed for the rearing of post-smolts during a limited period after seawater transfer. Keratocytes rapidly migrate to cover wound surfaces with the ability to internalize particular matter as part of the nonspecific immune response[11,12] Removal of this outer layer of fish skin may increase susceptibility to infections[7,9]. The goal of this study was assessment of conditions and temporal changes in salmon skin from smolt in freshwater to post-smolt in the first period after seawater transfer, and comparison between a S-CCS and conventional open sea net-pens. These results further indicate that it may be beneficial for salmon to spend the first months in a more controlled and confined environment
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