Survival potential and chromosomes of progeny of triploid and pentaploid females in the loach, Misgurnus anguillicaudatus

Abstract

Triploids resulting from reciprocal hybridizations between natural tetraploid and diploid loach laid two types of eggs: large and small. Triploid males had no functional spermatozoa. Pentaploid fish were induced by inhibiting the second polar body release after crossing tetraploid female and diploid male. Pentaploid females also produced eggs, but their eggs were intermediate in size between the large and small eggs of the triploids. The eggs of triploids and pentaploids fertilized with haploid normal spermatozoa produced viable progeny. Viable offspring were also obtained from the eggs fertilized normally and then subjected to hydrostatic pressure to inhibit polar body release. A small number of gynogenetic progeny of triploids, induced with ultraviolet-irradiated spermatozoa, survived. Chromosomal characterization of these progeny demonstrated that triploid females formed tetraploid (3n egg and 1n polar body), pentaploid (3n egg and 2n polar body), and hexaploid (3n egg and 3n polar body) mature ova of large size as well as diploid (1n egg and 1n polar body) ova of small size. Pentaploid females laid only tetraploid (2n egg and 2n polar body) ova. Oogenic mechanisms are discussed to account for the formation of these various types of ova in triploids and pentaploids derived from natural tetraploid loach.