Fast growth was not associated with an increased incidence of soft flesh and gaping in two strains of Atlantic salmon (Salmo salar) grown under different environmental conditions

We tested the hypothesis that fast growth prior to harvest increased the incidence of soft flesh and gaping in Atlantic salmon (Salmo solar L.) fillets. Growth trials were conducted at Salar, South Uist Westem Isles, Scotland and at the Gildeskal Research Station-Gifas, Northern Norway in duplicate 5 m x 5 m x 5 m net pen sea cages, and feeding commercial diets. Individual growth rate was measured as the thermal growth coefficient (TGC) and a range of flesh quality attributes were measured including fillet firmness using an instrumental t.-xture analyser. The Uist trial comprised the offspring of seven families from the Stofhfiskur breeding programme (Stofnfiskur A/S, Iceland). Salmon from the Uist trial harvested in October 2003 had an average TGC of 2.1 (range 1.4 to 3.6) and showed a very minor but significant positive relationship between the work done (WD) (mJ) to shear a standardised fillet slab and TGC (R 2 =0.041; degrees of freedom 160; P=0.01). In the Gifas trial 1200 PIT-tagged 03 input Sl smolt of the NLA strain were tightly graded and stocked into 4 net pens in June 2004 at a mean weight of 1447 g (16% coefficient of variation). In order to gain salmon with a wide spectrum of growth rates of comparable harvest weight the fish were fed in duplicate cages either to satiation or restricted ration to target a lower growth rate whilst maintaining the same feed conversion rate. In September 2004 104 fish were harvested, selected for high growth rates (TGC = 3.7 +/- 0.06, mean SE; range 2.6 to 5.0) and 106 lower growth rate fish' (TGC=2.7 +/- 0.04, mean:LSE; range 1.7 to 3.6) were harvested in November 2004. For the September harvest there was no relationship between TGC and WD whereas for the November harvest there was a very minor but significant negative correlation between TGC and WD (R-2 = 0.046; degrees of freedom 102; P = 0.04). There was no relationship between TGC and the incidence of gaping 3d post-rigor as measured by the length (cm) gapes m(-2) fillet cross-sectional area (Uist trial) or gaping score (0=no gaping to 4=:severe gaping) (Gifas trial). In practical terms it was concluded that there was no evidence that fast growing fish had a materially higher incidence of soft flesh and gaping than slow growing fish for the stocks and sites studied. (c) 2007 Elsevier B.V All rights reserved.