| Yadong trout (Salmo trutta fario) is an important and characteristic aquaculture fish species in Yadong, Xizang, China. At present, the farmed Yadong trout have been produced on a large scale. Two different-colored eggs (yellow and orange) are usually produced during the Yadong trout farming, and these eggs performed differentially in reproductive performance. There has been very little information about the nutrient composition of eggs with different colors. Relevant results have been reported only on rainbow trout. The present study was aimed at analyzing the nutrient compositions in Yadong trout eggs with different colors, in order to elucidate the factors responsible for the different reproductive performances of the two egg types. This experimental samples were collected from Yadong Industry Park, where the broodstock were reared with artificial compound feeds. Each type of egg was analyzed in 3 replicates. Yellow eggs were produced by broodstock of 2-3 years old, and orange eggs were produced from broodstock of 3-5 years old. After spawning, the eggs were cryopreserved and transported to the laboratory by plane. The samples were lyophilized and used for the determination of proximate composition, fatty acids, amino acids, and other reproduction-related nutrients. The crude protein and crude lipid content was analyzed with the Kjeldahl method and Soxhlet extraction method, respectively. The fatty acid composition (expressed as % total fatty acids) and amino acid composition (expressed as % dry matter) were assayed with gas chromatography and automatic amino acid analyzer, respectively. The protein carbonyl and malondialdehyde concentration was assayed with commercial kits supplied by Nanjing Jiancheng Bioengineering Institute. The α-vitamin E and astaxanthin were assayed with national standard methods, and the α-vitamin E was measured with wet samples. The statistics of proximate composition, fatty acids and amino acids data used T test for independent samples. The results were expressed as mean ± standard error. The results showed that yellow eggs had lower contents of crude protein and ash contents, but higher contents of crude lipid and moisture than orange eggs. There was no significant difference in carbohydrate and energy content between yellow and orange eggs. The saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (n-3PUFA) and DHA contents of yellow eggs were significantly lower than those of orange eggs, while the n-6 polyunsaturated fatty acids (n-6 PUFA) and EPA contents were not significantly different between the two egg types. The C16:0 and C20:0 contents of yellow eggs were significantly lower than those of orange eggs, while the contents of monounsaturated fatty acids (MUFA), including C16:1n-7, C18:1n-9, C20:1n-9, and C22:1n-9, of yellow eggs was significantly higher than those of the orange eggs. The contents of essential amino acids (EAA), non-essential amino acids (NEAA) and total amino acids (TAA) were slightly lower in yellow eggs compared to orange eggs. Among the essential amino acids, the contents of valine, methionine, leucine, lysine and histidine in yellow eggs were significantly lower than those in orange eggs. Among the non-essential amino acids, except for glycine and alanine, of which the contents were significantly lower in yellow eggs than in orange eggs, the contents of other amino acids were not statistically significant between the two egg types. The contents of protein carbonyl and malondialdehyde in yellow eggs were higher than those in orange eggs, while the contents of α-vitamin E and astaxanthin in yellow eggs were lower than those in orange eggs. In conclusion, orange eggs had higher contents of protein, some essential amino acids, DHA, α-vitamin E, and astaxanthin, but lower contents of MUFA, crude lipid, as well as peroxidation products, namely, protein carbonyl and malondialdehyde, than yellow eggs. These differences in nutrient composition may contribute to the superior reproductive performance of orange eggs to yellow eggs. |
