Induction of high triploid rate blunt snout bream (Megalobrama amblycephala) by hydrostatic pressure and analysis of gonadal sterility mechanism

Abstract

At present, only cold shock method was used to induce the triploid of M. amblycephala, and because the triploid rate is not high enough, the triploid fish has not been applied in aquaculture on a large scale. This study aimed to obtain the best induction conditions of triploid by hydrostatic pressure, reveal the reproductive characteristics and mechanism of gonadal sterility of triploid M. amblycephala, provide an insights into the meiotic patterns of triploid fish. We successfully induced triploid in M. amblycephala using the hydrostatic pressure method. The highest triploid rate reached 85.92% at 55 MPa for 3 min after 3 min of fertilization. The relative DNA content of the triploid fish was 1.5 times of that of the diploid fish, and their chromosome karyotype was 3n = 72 = 27 m + 39sm + 6st. Both female and male triploids had dysplastic gonads, the testis of triploid males was able to produce 1.5n sperm without fertility because all the hybrid embryos of 2n♀ × 3n♂ died; however, the ovaries of triploid females belonged to complete sterility. The verification of gene expression patterns and interaction suggested that the hypothalamus-pituitary-gonad (HPG) axis process was disturbed and unsynapsed chromosome (UC) axis was blocked may jointly caused the complete sterility without egg production of female triploids. However, triploid males belonged to uncompletely sterility, which can produce a small number of sperm and complete fertilization, but the offspring cannot survive, may caused by the not completely blocked UC axis with low expression of hormad1 and iho1.