Inheritance And Variation Of Major Traits In Hybrid F₁, F₂of Oreochromis Niloticus♀×Sarotherodon Melanotheron♂

In order to take advantage of brackish water resources in China and breed a goodbreed with ideal culture performance and high salinity tolerance, distant interspevifichybridization of Oreochromis niloticus and Sarotherodon melanotheron were carriedout by artificial hybridization,and O. niloticus♀×S. melanotheron♂hybridF₁wasobtained with fast growth and high salinity tolerance. Because of difficulty inhybridization and low success rate, hybridF₁can’t be directly applied for aquacultureproduction. Fortunately, hybridF₁could reproduce F₂, which inherited the heterosis andreproduced easily, F₂could be applied for aquaculture production. This study analysisthe inheritance and variation of genetic, morphology and growth traits in hybridprogenies of O. niloticus♀×S. melanotheron♂, in order to explore the stability andprovide a scientific basis for the breeding.Inheritance and segregation in the hybridsF₁, F₂of O. niloticus♀×S. melanotheron♂were preliminarily analyzed by microsatellite markers.21loci with different-sizedalleles in O. niloticus and S. melanotheron were selected from86pairs of microsatellites,59alleles were detected including22specific alleles in O. niloticus and16in S.melanotheron. The observed heterozygosity （Ho=0.998） inF₁was bigger than F₂（Ho=0.739）, while the effect number of alleles （Ne=2.48） and polymorphism information（PIC=0.497） in F₂were similar asF₁（Ne=2.45, PIC=0.489）. Heterozygous alleles wereobserved in all loci ofF₁, whereas different allelic separation were detected in F₂loci.Chi-square test showed, there were18loci followed the strict Mendelian segregation（1>P>0.05）, segregation distortion （P<0.05） existed in two loci （GM145, UNH003） andnonsegregation in locus GM276. Within the18mendelian loci, F₂possessed the sameallelic frequency of O. niloticus specific alleles were48.3%and S. melanotheron specificalleles were47.7%, genotypes frequencies ofF₁type, O. niloticus type, S. melanotherontype observed in F₂was58.2%,19.9%and21.9%, respectively. The above results showedthat hybridF₁exhibited the heterozygous genotype and inherited thoes specific allelesfrom O. niloticus and S. melanotheron respectively, there was no signififcant differencein the genetic heterozygosity between F₂andF₁. Inheritance and segregation of morphology in hybridsF₁, F₂of Oreochromis niloticus♀×Sarotherodon melanotheron♂were analyzed by ANOVA, cluster analysis,discrimination analysis and principle analysis with6countable morphological parameters,11meristic parameters and24ratio parameters. The results showed that:（1） hybridF₁, F₂were similar between O. niloticus and S. melanotheron in countable morphologicalparameters; but in meristic and ratio parameters, hybridF₁significantly improved than O.niloticus in body thick/total length, body height, body length, the head （snout length/totallength, eye diameter/total length, D1-2/total length, D1-6/total length, D2-3/total length, D2-4/total length, D3-4/total length, D4-6/total length）, the tail （caudal peduncle height/totallength, D7-10/total length） and significantly improved than S. melanotheron in the bodylength/total length, the trunk （trunk length/total length, D3-5/total length, D6-8/totallength）, the tail （tail length/total length, caudal peduncle length/total length, D5-7/totallength, D7-10/total length, D8-10/total length）. There were no significant difference betweenhybrid F₂andF₁in most morphology characters, but significant improved in the head（head length/length, eye diameter/total length, D1-3/total length, D1-6/total length）, thetrunk（D3-5/total length, D3-6/total length, D5-6/total length, D5-8/total length）, the tail（D7-8/total length, D7-10/total length, D9-10/total length）.（2） cluster analysis showed the hybridF₂andF₁were similar and both more similar with O. niloticus than S. melanotheron.（3）The discriminant accuracy of two discriminant formulations were O. niloticus and S.melanotheron> hybridF₁>hybrid F₂; most hybridF₁individuals were sentenced to O.niloticus by the discriminant formula of O. niloticus and S. melanotheron, which showsmatroclinal inheritance; Most hybrid F₂were sentenced to hybridF₁by the discriminantformula of O. niloticus, S. melanotheron and hybridF₁, few were sentenced to O. niloticusand S. melanotheron, it further proved hybrid F₂was similar as hybridF₁.（4） Principalcomponent figure showed that hybridF₁, F₂distributed between O. niloticus and S.melanotheron, but most overlapped with O. niloticus, hybrid F₂also overlapped with S.melanotheron. All above results showed that the hybridF₁showed interspecificmorphological traits and maternal inheritance, hybrid F₂were similar to hybridF₁inmorphology.The growth and morphological traits of hybrid F₂distribution were explored bycontrasting with O. niloticus, the results showed that:（1） Hybrid F₂grew more slowlythan O. niloticus in freshwater within117days; The percentage of the instantaneous growth rate, absolute growth rate and the final weight of hybrid F₂were85.6%,62%,63.6%in O. niloticus, respectively; but the grossness degrees and weight variationcoefficient of hybrid F₂increased by25.9%and37%than O. niloticus.（2） The variationcoefficient of the traditional morphological traits of hybrid F₂, such as body length, bodyheight, body thickness, increased by36%and those traits distribution curve was more flatthan O. niloticus. Some deviation in body color and stripes in tail were observed in hybridF₂. The above results showed the hybrid F₂had a certain discrete degree in growth andmorphological traits.