Body composition and sensory assessment of three weight groups of Atlantic halibut (Hippoglossus hippoglossus) fed three pellet sizes and three dietary fat levels

In the present investigation, we tested the effects of varying initial fish weight (0.8 to 1.8 kg), pellet size (12-27 mm phi), dietary fat level (10-39% of dry matter) and their cross-terms upon the fat content in a standardized fillet cut of farmed Atlantic halibut (1.3-2.7 kg) after 6 months. A factorial design (FD, 2(3)) plus four centre points was applied. The fish were individually tagged and reared at a mean temperature of 8.2 degree C. Lipid content in the fillet was modelled with the aid of PLS (partial least squares) regression on size and sex subgroups. A sensory panel consisting of 11 trained assessors tested the effects of final fish weight and dietary fat contents on multiple sensory parameters. These data were analysed by ANOVA and principal component analysis (PCA). Wide intra- and interindividual variation in fat content were observed. A standard Atlantic halibut fillet quality cut (A) is suggested for future work on fillet quality, together with measurements of fat along the dorsal and the ventral fin base. The PLS models of lipid deposition in the fillets showed a positive influence from increased initial fish weight and increased dietary fat content. Pellet size showed a minor positive contribution to the fat deposition in the fillet. The sensory test showed that larger halibut (2.1-2.7 kg) fed diets containing 20 or 39% fat were characterized by a fresher and more acidic flavour and a more juicy consistency, compared to smaller fish (1.4 kg), irrespective of the small fish groups' dietary regime. The smaller fish were characterized by rancid flavour and off-flavour. In addition to the sensory data, the evaluation of the feed from a feed production viewpoint showed that it is more economical to utilize herring filleting offal to produce a high fat feed (39%) that ensures the same fillet quality in the Atlantic halibut as the medium fat feed does. We, thus, conclude that the fat content in the feed for Atlantic halibut should be optimized at a level near 40% in due time before the slaughtering period, and that the fish preferably should pass 2.0 kg before being slaughtered.