Mechanical properties of the vertebral column and ribs of farmed fish with emphasis on Atlantic Salmon

The main aim of the thesis was to characterize mechanical properties of the vertebral column and ribs of Atlantic salmon and to recommend a method for measurements of mechanical properties of vertebrae and ribs. Every fourth vertebrae and every second rib was analyzed within the same weight class (4 kg) of salmon. Additionally, variation in MP mechanical properties among 4 kg, 5 kg and 6 kg salmon vertebrae and ribs, between salmon, rainbow trout and common carp, and the effect of frozen storage were analyzed. The instrument used was TA-XT2 Texture Analyzer. Samples collected from three different section in vertebral column of salmon and trout were chemically analysed for fat content, dry matter and ash. The results showed significant variation in mechanical properties along the vertebral column, between weight classes, between the fish species, and between fresh and frozen vertebrae. There was not a consistent relationship between thickness and the mechanical properties. The mechanical strength of the ribs decreased in the posterior direction, with the highest strength closest to the vertebral column. The fat content of the salmon vertebrae (17-22%) was higher compared with trout (11-15%), while the ash content was higher of trout (21-23%) compared with salmon (17-18%). Vertebrae which had been frozen also proved useful for mechanical measurements. Based on results from this study, the recommended method for analyzing mechanical properties of salmon is to analyse vertebrae 12 to 28 (counting from tail) because of the stable mechanical properties within this range, and hence low risk to conclude wrongly due to mistaken counting. The total work (N*sec) required to compress the vertebrae to 70% of total thickness was the most representative parameter for data analyses. The method was also applicable on Rainbow trout. The rib located nearest the head, measured at a position close to the vertebral column, proved the best option for detecting representative variation of mechanical properties of salmon ribs.