Reproductive ability of second generation ornamental (koi) carp ( Cyprinus carpio L.) × goldfish ( Carassius auratus L.) hybrids and characteristics of their offspring

Abstract

The purpose of this study was to investigate the reproductive ability of second generation (F2) koi (Cyprinus carpio L.) × goldfish (Carassius auratus L.) hybrids. Only diploid F2 males and females were fertile and used in crosses. A significant increase was recorded in male fertility in F2 versus F1. In contrast with an earlier study in which only one fertile F1 male was found, about 20% of F2 males produced sperm. The observed reproductive ability of F2 hybrids was similar to that demonstrated by the only fertile F1 male and F1 females. F2 males produced diploid spermatozoa and generated triploids when crossed with koi females. All triploid fish in these progenies were males indicating that F2 males had a sex chromosome constitution of XY. F2 females produced diploid eggs and generated mostly triploids when crossed with koi males. In progenies obtained by crosses of F2 males with F1 and F2 females, most of the surviving juveniles (63%–100%) were diploid; a minority of juveniles were aneuploid (ploidy ranged from 2.1n to 3.6n). Diploid fish in these progenies were presumably the result of spontaneous androgenesis and gynogenesis, by the same mechanisms observed earlier in progenies obtained by crossing the F1 male with F1 females.