The effects of diet, feeding regime and catch-up growth on flesh quality attributes of large (1Â + sea winter) Atlantic salmon, Salmo salar

A 122-day sea trial was undertaken in the summer/autumn of 2001 to evaluate the effects of diet, feeding regime and catch-up growth on the flesh quality of 1 + sea winter Atlantic salmon. Two diets, extremely high- or medium-energy (XE ∼ 39% and ME ∼ 33% oil, respectively), were fed to satiation or restrictively (80% of recommended ration) to salmon in 24 seawater pens. Feeding intensities were reversed mid-way through the trial for half the replicates, creating 8 feed/feeding combinations. The fish grew from approximately 3.8 kg to between 6.5 and 7.6 kg, with specific growth rates (SGR) ranging from 0.44 to 0.58% day− 1. Growth depended on the combined effects of dietary energy level and feeding intensity (dietary treatment). Fish fed the XE diet grew faster than ME-fed counterparts and feeding to satiation produced higher growth rates than restrictive feeding. Catch-up, or compensatory growth was observed amongst salmon fed to satiation after initial restrictive feeding. These fish had significantly higher SGRs than all other treatment groups during the catch-up growth phase (P < 0.0001) and grew to a size equal to that of their unrestricted conspecifics. Condition factor and carcass yield increased throughout the trial irrespective of diet type or feeding intensity. Visually assessed colour, using the Roche SalmoFan™, was unaffected by diet or feeding intensity however instrumental readings for chroma and hue° increased irrespective of diet type or feeding intensity. At harvest, fat content was influenced by the combined effects of diet and feeding intensity, but when fish size was taken into consideration these influences were lost (P = 0.5192). No relationship between fillet fat content and texture was found irrespective of treatment (r2 = 0.0006, P = 0.7819) and instrumentally measured texture was unaffected by diet, feeding intensity and growth rate. The extent of free oil (flesh oiliness) increased throughout the trial, but was similar amongst fish from all treatment groups. Feed type and feeding level significantly affected growth, but had little impact on the assessed quality attributes or incidence of free oil. These same attributes were unaffected by catch-up growth.