Genetic Variation Of Crossbred Progeny Of Heckel×Turquoise Discus And Marlboro Discus×Ruby Red Discus

Fish hybrid breeding is the most common and basic method in fish breeding,which includes distant hybridization and relative hybridization.Morphological difference analysis and ribosomal 5S gene sequence analysis are two common methods for fish hybrid identification.two pairs of discus fishes were selected for hybridization pairing,and the traditional morphological characteristics,frame parameters and 5SrDNA sequences of parents and F1 generation were analyzed in this study,There are few studies on crossbreeding of discus fishes currently,because of the difficulty in matching them.After successful pairing of Heckel discus(Symphysodon discus Heckel)and Turquoise discus(S.discus Turquoise),Marlboro discus(S.aequifasciatus aequifasciatus.sp)and Ruby red discus(S.aequifasciatus aequifasciatus.sp),their offspring were studied in this paper.Based on morphological analysis and ribosomal 5S gene sequence analysis,the genetic variation of hybrid progeny was investigated in order to be helpful to hybrid breeding and breeding of the improved species of discus fish.The main contents of this paper are as follows:1.After a male Heckel discus and a female Turquoise discus were crossbred,a total of 162 offspring(divided into color pattern group and black pattern group)were successfully obtained.The color pattern group had similar patterns and black longitudinal stripes to both parents,while the black pattern group had only black longitudinal stripes,but no patterns.At the time,a male Marlboro discus and a female Ruby red discus also were crossbred,then a total of 236 offspring(divided into black pattern group and no pattern group)were successfully obtained.The black pattern group showed the black yarn which was not found in the parents,and the black longitudinal stripe was not obvious.The no pattern group was similar to the parent group,and there was no pattern and black longitudinal stripe,and the body color was close to that of the parent group.2.The traditional morphological parameters and frame parameters of F1 generation aged 6 months were measured,and 7 items of traditional quantifiable characters and 18 items of frame parameters were selected for T test.,principal component analysis and cluster analysis.The results of T test showed that Heckel discus was similar to color pattern group in head,body height and caudal stalk,and to black pattern group in head,body length and caudal stalk in the cross between Heckel discus and Turquoise;The Turquoise was similar to the color pattern in the head and caudal stalk,and to the black pattern at the tip of the tail and the end of the kiss to the starting point of the pectoral fin.While in the hybrid experiment of Marlboro and Ruby red,Marlboro was similar to black pattern group,and similar in body length,body height,head and tail stalk to no pattern group;The Ruby red was similar to the black pattern group in head,body length and kiss end to pectoral fin starting point,and similar to no pattern group in tail stalk,body length,body height and kiss end to pectoral fin starting point.The results obtained by principal component analysis were as follows: in the hybrid experiment of Heckel and Turquoise,the main parameters of heavy load were the characteristics of the rostral to the starting point of the abdominal fin,the gluteal fin and the head,while in the hybrid experiment of Marlboro and Ruby red,the characteristics of body length and gluteal fin were the main parameters of heavy load.The results of cluster analysis showed that the Euclidean distance between color pattern group and black pattern group was the smallest in the hybrid of Heckel and Turquoise,it was 0.114,0.487 with Heckel,1.203 with Turquoise;The Euclidean distance between black pattern group and Heckel group was 0.553 and 1.244 with Turquoise,whose Euclidean distance is the largest one.The morphology of the two hybrid F1 generations is the closest to that of Heckel and the difference is small.While in the hybrid of Marlboro and Ruby red,the Euclidean distance between the no pattern group and the black pattern group was the smallest,with the distance of 0.284,and between the no pattern group and the Ruby red group was 1.374.In the hybrid of Marlboro and Ruby red,the Euclidean distance between the pattern group and the black pattern group was the smallest(0.284).The Euclidean distance between Ruby red group and no pattern group was 1.374,and that of Marlboro was 0.603.The distance between Marlboro and no pattern was 1.109,which was the closest between parents and offspring.The shape of offspring was closer to Marlboro.3.After 5S rDNA sequencing of the parents and their F1 generations,the structure and variation were analyzed and a phylogenetic tree was constructed.It was found that Heckel had 210 bp and 300 bp 5S rDNA structural units in the hybridization experiments of Heckel and Matsushita,and that the Matsushita and daughter generation only had a 210 bp 5S rDNA structural unit.The CG content in the coding area of the color pattern group was 55.0%,the CG content in the Heckel coding area was 58.33%,and the CG content in the coding area of the Turquoise and the black pattern group were 57.5%.The 5S rDNA coding region sequence of the two parents differed by several bases,and the progeny had a certain degree of variation in the coding region sequence compared to the parent.Phylogenetic tree analysis showed that the genetic relationship between Heckel and color pattern groups was closer,and the relationship between Turquoise and black pattern groups was closer.While,in the hybridization experiments between Marlboro and Ruby red,the ratio of CG base pairs in the coding region of the Marlboro,Ruby red,and no pattern groups was 57.5%,and that of the black pattern group was 59.66%,and their sequence of the 5S rDNA(deoxyribonucleic acid,DNA)coding region is also somewhat different.According to the phylogenetic tree analysis,the genetic relationship between the red glutinous group and the non-patterned group was the closest,and that of the red peony group was the farthest relative to the black patterned group.In summary,all measured 5S rDNA sequences consisted of a 21 bp(Base Pair)3’ end coding region,a complete NTS region,and a 99 bp 5’ end coding region.By comparing their 5S rDNA sequences,their coding regions are more conserved than in the coding regions.The proportion of GC bases in all measured sequences is relatively high.In the 5Sr DNA coding region of all discus fish,there are internal control regions(ICR,transcription promoter)elements,including Box A,Box C,and IE elements.By comparing their 5S rDNA sequence,their gene sequence of coding region was relatively conserved,while that of non-coding region was significantly different.The proportion of GC bases in all measured sequence was relatively high.In the 5Sr DNA coding region of all discus fish,there were internal control regions(ICR,transcription promoter)elements,including Box A,Box C,and IE elements.