Composition Analysis of Farmed and Wild Yadong Trout (Salmo trutta fario)

Abstract

Yadong trout (Salmo trutta fario), the only salmonid fish in the Tibetan Plateau, is a national agricultural product with geographical indications in Yadong. The development of Yadong trout aquaculture has significant implications for local farmers. However, no study has yet investigated the nutrient requirements of this fish. This study aimed to analyze the proximate amino acid, and fatty acid composition of various tissues of wild and farmed Yadong trout, in order to provide a reference for the evaluation of fish fillets and the formulation of optimal feed. Ten wild fish captured in the Yadong River, and 10 fish farmed with formulated feed in Yadong Industry Park were used in this study. The farmed fish were F1 generation wild broodstock captured in the Yadong River and fed formulated feeds throughout their lifetime. The body length of wild Yadong trout was in the range of 13.4~28.7 cm, and the body weight was in the range of 38.48~346.85 g. The body length and body weight of farmed Yadong trout were in the range of 16.4~24.5 cm and 78.39~275.29 g, respectively. Frozen samples were transported to the laboratory by flight. The proximate composition of whole fish, muscle, and liver; fatty acid composition of whole fish and various tissues including muscle, liver, intestine, brain, and eye; as well as amino acid composition of whole fish, muscle, and liver were analyzed. The fatty acid composition (expressed as % total fatty acids) and amino acid composition (expressed as % dry matter basis) were assayed using gas chromatography and an automatic amino acid analyzer, respectively. In addition, t-tests were performed for independent samples; results are expressed as the mean ± standard deviation. The results showed that wild fish had lower condition factors but higher moisture and ash content than farmed fish. Wild fish muscle had lower crude lipid content but higher moisture content than farmed fish. The whole-body protein and lipid contents, as well as the proximate composition of the liver, were not significantly different between wild and farmed fish (P > 0.05). The contents of saturated fatty acids (mainly C16:0 and C18:0) and n-3 polyunsaturated fatty acid (PUFA) in whole fish, muscle, and liver were significantly higher (P 0.05) was observed in other amino acids. These results indicate that wild Yadong trout were leaner than farmed trout in terms of muscle lipid content. For trout, which are mainly consumed fresh, this trait may make farmed Yadong trout more acceptable than wild trout. However, in terms of fatty acid composition and amino acids, the wild Yadong trout seemed to be more acceptable than farmed trout. In particular, n-3 PUFA content is an important nutritional trait in fish fillets. The wild Yadong trout had higher n-3 PUFA contents than the farmed trout. Thus, the fish oil in the feeds of Yadong trout should not be omitted, considering that fish chemical composition generally reflects that of their diets. In addition, the price of alternative oils such as soybean oil is no longer low; the use of lipid sources in the diets of Yadong trout should be reviewed. Similarly, the essential amino acid content in wild Yadong trout was higher than that in the farmed trout, suggesting that the protein sources should be reviewed, and a certain level of fish meal should be guaranteed. In conclusion, the results of this study indicate that the formulated feeds of Yadong trout need to be further optimized.

Keywords

• salmo trutta fario
• wild
• farmed
• nutrient composition
• amino acid
• fatty acid