Dietary impacts of sulphuric acid extracted fish bone compounds on astaxanthin utilization and muscle quality in Atlantic salmon (Salmo salar)

The aim of this study was to evaluate how a fish bone hydrolysate (FBH) from blue whiting (Micromesistius poutassou) fish bones may improve muscle astaxanthin (Ax) deposition in Atlantic salmon (Salmo salar). Fish (1.7 kg) were reared in 12 net-pens and fed with one of four practical formulated diets for 78 days. All diets (D) were balanced to meet dietary phosphorus (P) requirement (8 g kg−1 P): the control diet (D1) and diet D4 were added CaPO4 as P source, diets D2 and D3 were added P from a spray dried FBH ingredient at 2.1 and 4.2%, respectively, and D2 was further balanced with CaPO4. Diet D4 was added K2SO4 to study potential impacts of sulfate in H2SO4 used for mineral hydrolysis. An in vitro cell culture trial with hepatocytes (600 g salmon) was performed to study the effects of FBH on Ax uptake and transport. The soluble fish bone compounds significantly increased specific muscle Ax retention (mg kg−1 weight gain) by 35% (P < 0.05) in fish fed D3, possibly explained by improved Ax digestibility (ns) followed by increased circulating Ax and a tendency towards increased tissue Ax deposition (ns). Reduced metabolic turnover of Ax was indicated, with about 10% more of absorbed Ax retained in muscle of fish fed D3. The in vitro trial showed no direct impact of FBH on hepatic Ax uptake. However, the FBH ingredient altered the muscle connective tissue by stimulating the production of proteoglycans and their sulfated glycosaminoglycans (GAGs) significantly. This study suggests that hydrolysed compounds from fish bones may improve Ax utilization in salmon, and that they may have an impact on the functional properties of the muscle.