Study On Induction Under Hydrostatic Pressure,muscle Quality And Microsatellite Genetic Characteristics Of Triploid Megalobrama Amblycephala

At present,the decline of germplasm resources in breeding population of Megalobrama amblycephala leads to the phenomenon of sexual precocity.Due to the shortage of good varieties and the long period of traditional breeding,we attempted to study on triploidy induction of blunt snot bream.The induced method by hydrostatic pressure was applied to breeding of this species for the first time.Under the condition that the control duration is 3 min,and the water temperature is 20℃,the induction effect of pressures and starting treatment time with different gradient have been preliminary explored.Studies have shown that the best induction conditions for triploidy are 3 min after fertilization,maintaining 45 MPa pressure.Under this treatment,hatching rate of fish egg is 76.43%,survival rate of fry is 72.85%.Induced rate of the triploid fish is 53.21%.We contrasted the growth performance among the diploid and triploid population,results showed that the average weight and absolute weight gain rate of triploidy were significantly higher than diploidy at 18 months(p<0.05),showing obvious growth performance.Gonadal development in triploid blunt snot bream at the breeding season was retarded compared to the diploid.Gonado-somatic indices(GSI)of triploid males and females were significantly smaller than diploidy.The value of diploid males and females were 4.8% and 21.7%.But the GSI also measured 1.9% and 1.3% for males and females of triploidy,respectively.In order to understand the muscle quality of female breams among different ploidy during the breeding period,the indicators related to the muscle sensory quality were studied.Muscle cellularity was different between both groups,such that muscle fibre density was higher for diploid specimens(p<0.05)and muscle fibres diameters were higher for the triploid(p<0.05).Several physico-chemical parameters(moisture,ash,protein,total fat,fatty acids)were analysed.The results showed that significant differences in moisture and protein content(p>0.05).Triploid flesh contained the highest(p<0.05)percentages of protein and moisture.Fat and ash content did not significantly(p>0.05)affected by inducing treatment of blunt snot bream.Ploidy did not affect pattern of fatty acid.In this experiment,the number of fatty acids that was tested from fishes is 19.There were 6 kinds of saturated fatty acids(SFA),4 kinds of monounsaturated fatty acids(MUFA),9 kinds of polyunsaturated fatty acids(PUFA).The saturated fatty acids of triploids was significantly higher than that of diploids(p<0.05),and the polyunsaturated fatty acids was significantly lower than that of diploids(p < 0.05).The monounsaturated fatty acids did not show significant differences between different groups(p>0.05).Compared with diploids,triploid blunt snot bream was closer to the appropriate n-6/n-3 ratio.The analysis results of the electronic tongue showed that the muscles of fishes from different populations had significantly different taste profiles.In terms of nucleotide composition,the inosinic acid and hypoxanthine of the triploid are significantly higher than those of the diploid.In summary,there are obvious differences in the sensory quality of the dorsal muscles that were obtained from the two types of ploidy female fish during the breeding period.In order to guide the breeding of triploid blunt snot bream,we compared the extent of genetic diversity of the triploid with diploid by using the microsatellite.The genetic variations of triploid and diploid stocks were assessed based on the selected20 microsatellite locis.The PCR products were isolated by polyacrylamide gel,and the microsatellite alleles were artificially identified and analyzed.The mean number of alleles for triploid and diploid breams were 2.75 and 3.05,the mean values of expected heterozygosity were 0.5061 and 0.5412,and the average of polymorphic information content were 0.4249 and 0.4783,respectively.Most of the locis were deviated from Hardy-Weinberg equilibrium,and the genetic deviation index of most loci showed excessive heterozygosity.By randomly selecting individuals in the two populations,the locis TTF1 and Mam-Est110 were able to identify triploids.Results of this research provided some reference for studying the genetic structure of the triploid,triploid determination and the breeding of triploid fish.