Seasonal variations in muscle growth dynamics and selected quality attributes in Atlantic halibut (Hippoglossus hippoglossus L.) fed dietary lipids containing soybean and/or herring oil under different rearing regimes

Atlantic halibut (Hippoglossus hippoglossus), 1630 ± 510 g at the start of the experiment were reared in tanks for 1 year and subjected to three different environmental regimes; Continuous light and Constant temperature (CC), Natural light and Constant temperature (NC) or Natural light and Ambient temperature (NA). Two diets were fed, where 50% of the dietary lipids were either herring oil or soybean oil supplemented. The fish were sampled in May, August and November the first year, and February and May the following year. The CC groups grew better than the NC and NA groups from May to November, and as a result had a significantly (p < 0.05) higher weight by the end of the experiment. This difference did however not affect muscle fibre size distribution, or the chosen muscle quality attributes texture, fat content, water or fat loss of the fillet. These quality attributes were influenced by season and body weight, whereas diet had no significant effect. The NA group had lower fat content of the fillet than the other environmental regimes in August, November and Mayend, and fat content increased with increasing fish weight. Water and fat losses were lowest in November and February. The diet influenced the fatty acid profile of the musculature; the triacylglycerol fraction reflecting the dietary treatment while the polar fraction was less influenced by diet. The hardness of the fillet was not influenced by the environmental regimes, but by season, and hardness was at its lowest in August, and increased towards the following spring. The muscle fibre distribution varied only with season, and neither treatment nor diet had any effect on the muscle growth dynamics. Recruitment of new fibres seemed mainly to occur during winter, signified by maximum occurrence of fibres < 500 μm2 by the end of the experiment in May.