Genetic Differences Analysis Of Monkey Flowerhorn,Classical Flowerhorn And Their Hybrid F₁

Flowerhorn（Cichlasoma spp,）,originating in Malaysia,also known as color snapper,etc.Through cross breeding,it is a brand-new ornamental fish species obtained by combining the excellent characteristics of several species of South American cichlids.The hybrid breeding of Cichlasoma has always been regarded as a highly commercial secret by flowerhorn farms.There are few reports about the hybrid breeding of flowerhorn fish.In order to further understand the morphological genetic relationship between the hybrid offspring and their parents,this study is investigate the appearance morphology and internal enzyme activity changes of monkey flowerhorn,classical flowerhorn and their hybrid F₁（classical♀×monkey♂,namely as GM）.The morphological research analyzed the morphological genetic relationship between the hybrid F₁ and its parents.The experiment of differential analysis of intrinsic enzyme activity was carried out.By comparing the enzyme activities of liver and gill of hybrid GM and its parents under normal feeding conditions and acute temperature stress,the effects of low temperature were analyzed.The purpose of this paper is to provide first-hand information and scientific guidance for the hybrid collocation,body improvement,variety selection and feeding management of cichlids.（1）Although both flowerhorns belong to different varieties,there are obvious differences in appearance between them,and the differences are mainly in the head,three fins and body color.Due to the continuous self-crossing,the genetic diversity of the species is reduced and the disease resistance is poor.The countable characteristics of them were basically the same in dorsal fin,pectoral fin,ventral fin,gluteal fin,lateral line scale,lateral line scales,lateral line scale,and so on,but there was no difference,so they could not be counted by countable characters.Based on the measurable shape,through statistical analysis,it was found that the hybrid offspring combined their parents’respective traits,and the hybrid GM was more inclined to classical flowerhorn in terms of three fins and fish body color,and the plant point and head traits on the body surface were more inclined to the male parent,which integrated the advantages of the monkey flowerhorn from the beginning and the female parent’s big three fins,showing excellent heterosis.By sorting out the obtained morphological data,eight morphological proportion parameters of classical flowerhorn（G）,monkey flowerhorn（M）and their F₁hybrids（Z）were compared by variance analysis,and it was found that Z had five proportions（body length/total length,body width/total length,tail stalk length/body length,tail stalk height/body length,and so on）.The ratio of Eye diameter/eye spacing was not significantly different from those of their parents,and one ratio（body height/body length）was comprehensive and significantly different from their parents（P<0.05）.In terms of hybrid index,7 items were biased towards G and 2 items were biased towards M.From the point of view of hybridization,the hybrid offspring combined their parents’respective traits,and most of the traits of hybrid offspring were biased towards G,only a few traits were biased towards M or between the parents.In general,the apparent morphological indexes of Z were greatly influenced by the G population.（2）Using GBS（Genotyping-by-sequencing）technology,the single nucleotide polymorphism（SNP）loci of 6 monkey flowerhorns,6 classical flowerhorns and 6hybrid F1（classical♀×monkey♂）were screened to construct the sequencing library.The results showed that the constructed reference genome contained 4481280 sequences in 18 samples.The average sequencing depth of all samples was.9.47.A total of 224064SNP loci were obtained by mutation site detection and filtration.According to the results of phylogenetic tree,the genetic relationship of hybrid fish is closer to that of the female parent,classical flowerhorn.In the analysis of population genetic structure,the minimum Cross Validation Error value was obtained when the ancestor value K=2,which proved that the theoretical ancestors of hybrid fish came from classical flowerhorn and Mawei flowerhorn.In terms of genetic diversity parameters,the population reached genetic balance,and the Fst values of group G,group Z and group M were 0.5706,0.8774 and 0.6004 respectively.The genetic distances（DR）were2.0988,0.4348 and 0.4514,all of which were>0.25,indicating that the offspring of the three groups were highly differentiated.The experiment of differential analysis of internal enzyme activity was carried out,and the antioxidant and MDA contents of MM group,GG group and their hybrid GM were analyzed.Under the same temperature conditions,the immune enzyme activity of the three groups of test fish,GG in acute cooling stress,the tissue cells were most severely attacked by free radicals,followed by MM,and the least attacked was GM.The temperature rose T5,the activity value of catalase（CAT）and malondialdehyde（MDA）content of liver were significantly different from MM and GG,the GM content of MDA was less than MM and less than GG,and the activity value of CAT was small and GG was less than MM.Glutathione peroxidase（GSH-PX）activity in liver tissues differed significantly between GM and MM and GG,and GM was significantly smaller than that of GG.Under warming stress,taking the change of MDA value in liver tissues as a reference,in the GG group,histiocytes were most severely attacked by free radicals in acute cooling stress,followed by MM and finally GM.Taking the activity value of GSH-PX in liver tissue as a reference,the antioxidant capacity of liver tissue,GM is less than MM and less than GG during the temperature drop process.Taking the activity value of GSH-PX in liver tissue as a reference,the antioxidant capacity of liver tissue during the temperature drop was anastomosed with the cooling to T3（16℃）,and the GM was less than that of MM and less than that of GG.In GM,liver and gill tissue antioxidant enzyme activity between maternal GG and paternal MM manifested as hybrid comprehensive inheritance.