Comparison of the proximate composition, amino acid composition and growth-related muscle gene expression in diploid and triploid rainbow trout (Oncorhynchus mykiss) muscles

The aim of the present study was to identify differences in the proximate composition, amino acid composition and expression of the muscle growth-related genes myogenic determining factor (MyoD) and myostatin (MSTN) in muscle between diploid and triploid female rainbow trout (Oncorhynchus mykiss) that were reared under the same conditions. The research included two different ages (12- and 16-month) of diploid and triploid rainbow trout. The lipid and protein contents of the triploid fish were significantly higher while their moisture content was significantly lower than those of the diploid fish. The amino acid compositions of the proteins of both diploid and triploid rainbow trout were well balanced. The percentages of total amino acids (WTAA), essential amino acids (WEAA), non-essential amino acids (WNEAA) and delicious amino acids were similar between the triploid and diploid fish. The WEAA to WTAA and WEAA to WNEAA indices were comparable to the reference values of nearly 40% and above 60%, respectively, recommended by the FAO/WHO. According to the amino acid scores, phenylalanine can be described as the first limiting amino acid, and the sum of methionine and cysteine represented the highest protein score in both diploid and triploid rainbow trout. MyoD1 mRNA expression was higher in triploid fish, while MSTN2 mRNA expression was higher in diploid fish. The growth potential was greater in triploid fish than in diploid fish. This study shows that both diploid and triploid rainbow trout are good protein sources; triploid rainbow trout is under further investigation due to presenting higher, balanced nutritional quality and better growth than the diploid fish.