| Mandarin fish is one of the traditional and precious fishes in China.The main cultured species are Siniperca chuatsi and S.scherzeri,which are carnivorous fishes.However,their appearance,growth,and feed coefficient are distinctly different.At present,a new hybrid "S.scherzeri ? × S.chuatsi ?(GS 02-005-2014)" has been obtained using hybridization breeding method.In view of the obvious results of crossbreeding between the mandrain fishes,the backcross progenies,S.scherzeri ? ×(S.scherzeri ? × S.chuatsi ?)were obtained.Firstly,the thesis compared the appearance(body spot and body shape),growth and feeding characteristics among the backcross progeny,S.scherzeri and hybrid at the early stage.Secondly,the body shape characteristics of backcross and parental progeny were compared using multiple comparisons and hybrid indices,and the morphological analysis was carried out using principal component analysis and discriminant analysis,and preliminary statistical analysis of body spot of backcross progeny was investigated.Thirdly,backcross and parental progeny were genetically distinguished by microsatellite markers and their genetic characteristics were compared.(1)Early morphology,growth and feeding characteristics of the backcross progeny of mandarin fish.The results showed that at 45 days age,the backcrossing progeny was similar to S.scherzeri with linear and regularly spot,while they were sparse and disorderly arranged in the hybrid.The head angle of the backcrossing progeny,S.scherzeri and the hybrid was(25.48 ± 0.85)°,(24.52 ± 0.65)°,(29.44 ± 1.34)°,and the body height / body length was 0.26 ± 0.03,0.25 ± 0.09,0.32 ± 0.05,respectively.Body shape of the backcrossing progeny resembled to S.scherzeri.On the 45 days age,the average total length was 78.52 ± 1.55 mm,55.51 ± 0.71 mm,83.81 ± 1.22 mm,average daily intake was 0.217 ± 0.02g/d,0.153 ± 0.01g/d,0.220 ± 0.04g/d,the feed coefficient was 2.99 ± 0.16,4.40 ± 0.22,and 2.76 ± 0.13,respectively.The feed coefficient of the backcrossing progeny and the hybrid was significantly lower than that of S.scherzeri(P < 0.05).All in all,it showed that the backcrossing progeny was similar to S.scherzeri in body spots and body shape,while the growth,average daily intake and feed coefficient were similar to the hybrid.(2)Comparison on morphology and body spots characteristics between the backcross progeny and their parents of mandarin fish.The results showed that the average hybrid index of the backcross is 38.73,the morphometric difference analysis and hybrid index show that the backcross progeny are biased toward S.scherzeri.Principal component analysis and discriminant analysis indicate that the main differences are in head angle,body height/body length,head height/head length,and C/body length between the backcross progeny and parents.The three-dimensional spatial distribution of the backcross,S.scherzeri and the hybrid on the first three principal components do not overlap and are distinguished from each other.Discriminant analysis can clearly classify three groups in two-dimensionals.The body spots of the backcross include back saddle spots,and trunk spots,4 types different combinations are classified,and 45.5% of the individuals have back saddle spots,and 72.8% have hollow spots.(3)Molecular identification and genetic characterization analysis between the backcross progeny and their parents of mandarin fish.15 interspecific microsatellite markers of S.chuatsi and S.scherzeri were obtained by screening.The backcross progeny can be distinguished from S.chuatsi by the SS236,CB179,and W19517 loci,and can be distinguished from S.scherzeri by the T075 loci.The average number of observed alleles(Na),the average number of effective alleles(Ne),the average Shannon information index(I*),the average observed heterozygosity(Ho),and the average expected heterozygosity(He)were the highest in the backcross progeny population,respectively 4.9091,3.4731,1.2421,0.6718,and 0.6288.Population of S.chuatsi had the lowest parameters,which were 1.9091,1.6442,0.4408,0.5424,and 0.2973,respectively,and the populations of S.scherzeri and hybrids were slightly changed.The genetic differentiation coefficient(Fst)and gene flow(Nm)showed that the genetic characteristics of backcross progeny was biased towards S.scherzeri(0.1384 and 1.5564).In summary,backcross progeny can be effectively distinguished from S.chuatsi and S.scherzeri by molecular markers;the genetic characteristics of backcross progeny are biased towards the recurrent parent S.scherzeri,and the genetic heterozygosity is the highest.The results can provide reference for molecular identification and genetic characteristics of the backcross of mandarin fish. |
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