Muscle and flesh quality traits in wild and farmed Atlantic salmon

Muscle characteristics that are important for flesh quality traits were assessed in populations of wild and farmed Atlantic salmon (Salmo salar L.). The wild fish were obtained from a commercial fishery on the North Esk, Scotland in 2001 and 2003. The farmed fish comprised 7 families from the Stofnfiskur breeding programme (Stofnfiskur A/S, Iceland) grown in 5 m × 5 m × 5 m net pen sea cages in a dedicated trial unit on South Uist, Scotland. Total carotenoid pigment (mg kg− 1 wet mass flesh) concentrations were higher in farmed (7.68 and 8.43 for grilse and salmon, respectively) than wild fish (5.53 and 6.44 for grilse and salmon, respectively). In contrast, the average flesh colour, measured with a SalmonFan™, was similar for all groups (27.4 to 28.0), indicating a superior colour visualisation per unit pigment concentration in wild fish. The flesh lipid content was 46%-higher (grilse) and 84%-higher (salmon) in farmed than wild fish. Vitamin E concentrations per unit wet mass lipid were similar in wild and farmed salmon and in the range (208–259 mg kg− 1). Fillet firmness was measured using a shear test and instrumental texture analyser. The work done (WD) to shear standardised post-rigor muscle samples was higher in grilse than salmon and was significantly greater for the wild (710 and 811 mJ, respectively) than farmed (415 and 602 mJ, respectively) fish, indicating a firmer texture in the wild fish. The grilse and salmon sampled had stopped recruiting fast muscle fibres and both wild and farmed fish had around 650,000 fibres per trunk cross-section. Thus differences in fillet texture and colour between these populations could not be explained by the muscle cellularity which was similar between groups. Hydroxyproline (HYP) was used to estimate collagen concentration. Alkaline-insoluble HYP was 72.5% higher in wild than farmed salmon (14.0 vs. 8.1 μmol g− 1 dry mass, respectively) whereas alkaline-soluble HYP was 5.2-fold higher in farmed than wild salmon (31.0 vs. 6.0 μmol g− 1 dry mass, respectively). The alkaline-insoluble collagen fraction is thought to be enriched with reducible and non-reducible cross-linked collagen. There was a significant positive correlation between pyridinoline (PYD) crosslink concentration and WD, explaining 25% of the within population variation in firmness. However, PYD concentration (pmol g− 1 dry mass) was similar between wild (476) and farmed (445) salmon and cannot explain the differences in flesh firmness observed between populations. It was hypothesised that the higher average values of firmness in the wild than farmed salmon flesh can in part be attributed to higher concentrations of reducible immature collagen crosslinks.