| 37 Schizothorax waltoni,38 Schizothorax o’connori and 37 their natural hybrids were collected from the Shigatse-Lhasa section of the Yarlung Zangbo River from June to July2021.In order to explore the classification status of their natural hybrids,establish the identification methods of the three fishes and explore their development potential in aquaculture and breeding varieties,the Cyt b(Cytochrome b)gene sequence of their mitochondrial DNA,external morphology and muscle nutrients were studied,the result as follows:1.The total length of Cyt b gene sequence of S.waltoni,S.o’connori and their natural hybrids is 1141 bp,and the base composition is similar.The phylogenetic relationship of six species of Schizothorax in the middle reaches of Yarlung Zangbo River is consistent with the phylogenetic relationship of external morphology and skeletal system,Cyt b gene has good adaptability in species identification of Schizothorax.The genetic relationship between 13 natural hybrids and S.waltoni is relatively close,and the genetic distance is0.004.The genetic relationship between 24 natural hybrids and S.o’connori is relatively close,and the genetic distance is 0.003.The genetic distance between the natural hybrid and its female parent is much smaller than that between the natural hybrid and S.macropogon,Ptychobarbus dipogon,S.younghusbandi,Oxygymnocypris stewarti(0.027～ 0.202),which maintains the genetic distance above the species level.S.waltoni and S.o’connori can be parents of each other and cross under specific natural environmental conditions.2.The external morphological characters of S.waltoni,S.o’connori and their natural hybrids were measured by traditional morphological measurement method and multivariable morphological measurement method.There were 40 proportional value of body length of each fishes to morphological characters were studied and analyzed by analysis of variance,principal component analysis and discriminant analysis.The analysis of variance showed that there were extremely significant differences in seven morphological traits among S.waltoni,S.o’connori and their natural hybrids(P<0.01).Seven principal components were extracted from principal component analysis,which mainly reflected the morphological changes of head,chest and body height.The discriminant function of the three external morphological traits was established,and the discriminant accuracy was 99.1%.According to the analysis results of Cyt b gene sequence,the natural hybrids were divided into natural hybrids with different female parents,and the discriminant functions of external morphological characters of the four were established.The discriminant accuracy of 8 personality entry functions was 91.8%.The discriminant accuracy of natural hybrids with S.waltoni as female parent was only 61.5%,and that of natural hybrids with S.o’connori as female parent was 87.5%.Based on the above results,the external morphological differences of the three are mainly concentrated in the head and chest.The three fishes can be effectively identified through the traits and discriminant functions with extremely significant differences,but the natural hybrids of different female parents cannot be accurately classified.3.The muscle nutrients of S.waltoni,S.o’connori and different female parent natural hybrids were detected with reference to the national standards for muscle nutrition testing implemented in 2017.The content of crude protein in muscle of S.waltoni was significantly higher than that of others,the content of crude fat in muscle of natural hybrids was significantly higher than that of their parents(P<0.05).The∑TAA(total amino acids),∑DAA(total delicious amino acids),∑EAA(total essential amino acids)of natural hybrids were higher than those of their parents(P>0.05).In terms of the relative content of fatty acids,the EPA + DHA in muscle of S.waltoni was the highest compared with the other three groups,the ∑SFA was lower than that of the other three groups,the ∑MUFA and∑PUFA were higher than that of the other three groups(P<0.05).The results show that S.waltoni is more in line with the nutritional characteristics of "high protein and low fat",rich in amino acids,reasonable fatty acid composition and higher nutritional value. |
