INDUCTION OF GYNOGENESIS IN GOLDFISH USING SPERMATOZOA OF BLUNT SNOUT BREAM

Abstract

Our previous studies reported that a new triploid fish was produced by crossing the females of goldfish(Carassius auratus Goldfish) with the males of allotetraploid hybrids of red crucian carp(♀) × common carp(♂).Compared this new triploid fish with Xiangyun crucian carp(Japanese crucian carp(♀) × allotetraploid hybrids(♂)),the new type of triploid crucian carp not only presented some advantages which the Xiangyun crucian carp had,such as faster growth rate,wider adaptability,sterility and stronger anti-disease ability,but also got some new good performances like the high ratio of the width to the length of the body and sweet flesh.Goldfish is a kind of the most important species of ornamental fish in China that has centuries-old feeding history,but it has poor capacity of disease resistance and adaptability and so on.As the female parent of the new type triploid hybrids,goldfish was highly expected to be genetically improved.In order to reach the aims,we used sperm from blunt snout bream(Megalobrama amblycephala) which were genetically inactivated by an appropriate UV dosage to activate the development of the egg of goldfish to artificial gynogenesis.In this paper,gynogenetic diploid was induced in goldfish eggs to gynogenesis using UV-irradiated spermatozoa from blunt snout bream,then the maternal DNA was duplicated with cold shock in the 0—4℃ cold water for 51—58 min to retain the second polar body.The experiment could obtain survivable individuals,and the fertilization rate,hatching rate and survival at the first feeding were(62.7±2.7)%,(30.1±4.3)% and(6.2±1.1)%,respectively.In this paper,we checked the individuals by morphological characteristics,chromosome number and the degree of gonadal development.Because blunt snout bream and goldfish belong to different subfamilies in zootaxy,using UV-irradiated spermatozoa of blunt snout bream not only can make the evaluation of gynogenetic status more easily,but also more easily to distinguish gynogenetic goldfish from the control hybrids just according to the chromosome number,the morphological characteristics and the degree of gonadal development.The successful gynogenetic goldfish generated offspring with 100 chromosomes,all of which were female that had double tails,looked like the goldfish and had normal gonadal.However,the individuals with 124 chromosomes were generated by hybrids of goldfish × blunt snout bream.They had single tail looked like the crucian,and the gonadal development was delayed.In the present study,it suggested that the spermatozoa of blunt snout bream were an effective activation source for inducing gynogenesis in crucian carp,and we could avoid exploring the genetic markers at the biochemic or molecular levels.This research obtained gynogenetic goldfish that no male was found in all gynogenetic goldfish examined randomly,and the presence of all female gynogenetic diploids matured at one year old provided cell genetics evidence to the goldfish's sex determination mode-XX/XY.Furthermore,the gynogenetic individuals had two types of offspring which had two kinds of color that were different from their female parent,and it might be conduced by allele homologizing or by allogynogenesis.