Production of Second Generation Progeny of Hexaploid Loach

Abstract

First generation of hexaploid loach Misgurnus anguillicaudatus, which had been produced by inhibiting the second polar body extrusion after fertilization in a natural tetraploid pair, were raised until the adult size. The sex ratio of these hexaploids did not deviate from 1:1, as predicted from the almost equal number of females and males in tetraploids as well as the all-female gynogenetic tetraploids. These observations suggested an involvement of the male heterogametic system in sex determination. Hexaploid females laid significantly larger eggs than tetraploids and diploids. Mature eggs of four mature hexaploid females (three were eu-hexaploid, while one was a hexaploid/tetraploid mosaic) were individually fertilized with spermatozoa of hexaploid (6n), tetraploid (4n), and diploid (2n) males. The progeny were viable and the majority of surviving fish from 6n female×6n male, 6n×4n, and 6n×2n crosses were hexaploid, pentaploid, and tetraploid, respectively. Fertilization of eggs of diploid and tetraploid females with spermatozoa of hexaploids (2n×6n and 4n×6n) gave viable tetraploid and pentaploid progeny, respectively. Thus, hexaploid loach formed triploid gametes (eggs and spermatozoa) and produced viable second generation progeny.