Effect of sustained exercise on white muscle structure and flesh quality in farmed cod (Gadus morhuaL.)

Growth performance and white muscle cellularity were investigated in Atlantic cod (Gadus morhua L.) (500–600 g) to determine if texture and thereby quality is affected by exercise. Three exercise regimes [low flow, 0.5 body lengths per second (BL s−1) and 1.0 BLs−1] were applied, and the experiment was run for 9 months, at which point the fish had reached around 2 kg body weight. There were no significant differences in fork length or condition factors between groups that could be attributed to the exercise treatment, but the 0.5 BL s−1 group had significantly lower body weight performance than the control group. The average specific growth rate ranged from 0.37% to 0.42% per day. Muscle fibre diameter was positively correlated with fish weight. However, there was no difference in the distribution of muscle fibre diameters between treatment groups. A texture analyser, model TA-XT2, equipped with a Warner–Bratzler shear blade was used to measure the texture of the fillet. No correlation was found between the shear force required to cut through the sample and the muscle fibre diameter, but the shear force decreased with increasing growth rate. A tristimulus colorimeter was used to measure the colour composition of the fillet instrumentally. Red/green chromaticity (a*) was positively correlated with the shear force. It was concluded that the exercise regimes tested were insufficient to influence either growth performance or muscle growth patterns. Individual variations in fibre diameter did not influence the colour or texture of the fillet.