Fertility and gamete ploidy of allopentaploid offspring of tetraploid dojo loach Misgurnus anguillicaudatus females and large-scale loach Paramisgurnus dabryanus males

Abstract

Artificial interspecific hybrids (3n) of tetraploid dojo loach Misgurnus anguillicaudatus (TTTT) and diploid large-scale loach Paramisgurnus dabryanus (PP) were viable. Allopentaploid loaches (TTTTP) were produced by cold-shocking the fertilized eggs of TTTT females fertilized with sperm of PP males. The TTTTP were viable and well developed. As there are currently no reports on the fertility and gamete ploidy of TTTTP, artificial propagation and ploidy analyses were conducted to determine them. The ovaries of TTTTP were well developed with primary oocytes and secondary oocytes; the testes were sterile with low-density sperm-like cells. By backcrossing with mature TTTT, TTTTP were found to be female fertile and male sterile. The fertility of female TTTTP was low; they produced few viable diploid eggs and a few inviable triploid and aneuploid eggs. Ploidy analysis of cold-shock-induced progenies of TTTTP × TTTT indicated that TTTTP could generate viable diploid eggs, along with diploid second polar bodies. The results of this study are helpful for further understanding of loach polyploidization and should encourage more investigations on hybridization and gamete formation in loaches.