Seasonal variations in growth, feed utilisation and product quality of farmed Atlantic salmon (Salmo salar) transferred to seawater as 0 + smolts or 1 + smolts

Seasonal variations in growth, feed utilisation, condition factor (CF), fillet fat content, colour, texture and gaping were studied in farmed Atlantic salmon transferred to seawater after 9 (0 + salmon) or 16 months (1 + salmon) in freshwater. The fish were weighed in bulk and sampled for quality assessment every second month over a 1-year period (July-July), and feed consumption was recorded daily. During the experiment, body weight increased from 0.20 to 3.37 kg in 1 + salmon and from 0.43 to 5.10 kg in 0 + salmon. The specific growth rate (SGR) decreased and feed conversion ratio (FCR) increased during late autumn and winter for both salmon groups, but the seasonal variations in SGR and FCR were largest in 1 + salmon. The initial CF was 1.1 for both salmon groups. The CF of the 0 + salmon stabilised at approximately 1.5 in November, whereas the CF of the 1 + salmon averaged 1.5 in May. The fillet fat content increased from 3-4% to 17-19% during the experiment, and the most pronounced fat increase occurred from July-November (12-13% units) in both 0 + and 1 + salmon. From November to July, the Roche Colour Card (RCC) score increased from 14.3 to 15.3 in 1 + salmon and 15.6 in 0 + salmon. Hardness, measured as breaking strength, was highest during the winter period. Breaking strength correlated negatively to SGR in both salmon groups, indicating that fast growth can promote flesh softening in salmon. The degree of fillet gaping was highest during spring and summer. To conclude, seasonal variations were observed in production efficiency and product quality in both salmon groups, but neither growth performance, feed utilisation nor product quality characteristics differed significantly between 0 + salmon and 1 + salmon when the data were corrected for weight differences.