Investigation On The Biological Characteristics Of The Hybrid Of Megalobrama Amblycephala(?)× Erythroculter Mongolicus(?)

Distant hybridization refers to crosses between two different species,genera,or higher-ranking taxa,which can break species limits,increase genetic variation,and combine the biological characteristics of existing species.Hybrids often exhibit heterosis in morphology,feeding ability,growth,reproduction and disease resistance.In this study,we carried out distant hybridization with female blunt snout bream?Megalobrama amblycephala,2n=48??namely BSB?and male mongolian culter?Erythroculter mongolicus,2n=48??namely MC?,and we successfully obtained a great number of viable hybrids.Through systematic research and comparative analysis,we found that all the hybrids were diploid individuals?2n=48?.To investigate whether the diploid hybrids?namely FBF₁?have heterobeltiosis,we conducted a comparative analysis including the morphological traits,DNA content,growth rates,chromosomal numbers,fertility,intermuscular bone numbers,pharyngeal teeth shape and intestinal characteristics between FBF₁ and their parents BSB and MC.Detailed contents and results are as follows:1.The fertilization rate,hatch rate and early survival rate of FBF₁were calculated and the results showed that FBF₁ had higher fertilization rate?80.4%?,hatching rate?63.5%?and early survival rate?88.6%?.DNA content and chromosomal numbers of FBF₁ blood cells were detected by flow cytometry and renal cell chromosome preparation techniques,respectively.The result shows that FBF₁'s DNA content is not significantly different from its parent's and contains the same number of chromosomes as the parent's?2n=48?.Therefore,these results indicate that FBF₁ is a diploid fish.2.Morphological measurements of ten-month-old FBF₁ were performed and compared with corresponding traits of their parents.In terms of measurable traits,we observed that each ratios of FBF₁ were intermediate between those of BSB and MC,and the ratio of total length/body length was significantly different?P<0.05?from those of their female parent BSB.In terms of countable traits,the number of ventral fins,anal fins,dorsal fins and lateral scales of FBF₁ was intermediate between those of BSB and MC.The number of upper lateral scales was closer to the male parent MC,and the number of lower lateral scales was closer to the parent BSB.Therefore,compared to the parent,FBF₁ showed obvious heterozygosity.3.The growth performance of FBF₁ and their parents at the ages of 1and 2 stages were measured and compared.At the 1-year-old stage,the average weight of FBF₁ was 56.18±10.26 g,which was significantly higher than that of MC?44.16±20.17 g?but had no significant difference with that of BSB?60.13±15.42 g?.At the 2-year-old stage,the average weight of FBF₁ was 1176.47±97.48 g,which was significantly higher than that of MC?568.16±156.32 g?and BSB?954.24±124.76 g?.Consequently,FBF₁ has more significant growth advantage than their parents.4.Fertility of FBF₁ was detected by using the gonadal section and sperm electron microscopy.The results showed that both female and male of FBF₁ had normal development of gonad at the 1-year-old.During the reproductive seasons,2-year-old female and male FBF₁ could produce mature eggs and sperm,respectively.After fertilization,a large number of surviving offspring of FBF₁ can be obtained.5.The numbers,morphology and distribution of intermuscular bones were measured and compared between 2-years-old FBF₁ and their parents BSB and MC.The results showed that the number of intermuscular bone of FBF₁ is 116-125??X=122?,while the female parent BSB and male parent MC were 114-124??X=120?and 133-150??X=141?,respectively.The number of intermuscular bones in FBF₁ was significantly less than that in the male parent MC?P<0.05?but was similar to that in the female parent BSB.For morphology,7 shapes of the intermuscular bones were observed in FBF₁ and their parents;besides,the intermuscular bones distribution showed relatively higher variation in trunk muscles than in the other body regions,but the number of intermuscular bones varies slightly on the left and right sides of the fish body.Therefore,compared with the male parent,FBF₁ has the advantage of less intermuscular bone.6.The morphology of the pharyngeal teeth of 2 years old FBF₁ and their parents were measured and compared.The results showed that the dentition of the pharyngeal teeth in BSB,MC and FBF₁ were 2.4.4-4.4.2,2.4.5-5.4.2 and 2.4.4-4.4.2,respectively.In the shape of the pharyngeal teeth,the types of major pharyngeal teeth in FBF₁ did not bias their parents,but the types of lateral pharyngeal teeth in FBF₁ were similar with MC.The combination types of both pharyngeal bone and pharyngeal teeth of FBF₁ were very similar with BSB.Therefore,judging from the shape of pharyngeal teeth,the feeding habits of FBF₁ were biased towards female parent with herbivorous.7.The characteristics and histological structures of the intestines of 2years old FBF₁ and their parents were measured and compared.The relative gut length?RGL?,relative gut mass?RGM?,Zihler's index?ZI?and relative gut density?RGD?of FBF₁ were significant higher than those in male parent MC?P<0.05?and were closer to female parent BSB.Besides,MC had the thickest intestinal wall,and BSB had the thinnest intestinal wall.The thickness of the intestinal wall of FBF₁ was between the parents and was closer to female parent BSB.These results further confirmed that the feeding habits of FBF₁ were biased towards their female parent BSB with herbivorous.In this study,a large number of surviving hybrid offspring were successfully obtained by intergeneric hybridization between female BSB and male MC.The hybrid offspring were all diploid individuals?2n=48?.Both female and male of FBF₁ were fertile and reached sexually maturity at the age of 2 years.The hybrids has faster growth rate than their parents,less intermuscular bones than male parent,and the feeding habits were herbivorous,indicating that they have a important application value in aquaculture.