Establishment of diploid hybrid strains derived from female Larimichthys crocea × male Larimichthys polyactis and transmission of parental mtDNA in hybrid progenies

In this study, a new type of diploid hybrid fish (LCP) was obtained successfully using interspecific hybridization of female Larimichthys crocea (LC, 2n = 48) and male Larimichthys polyactis (LP, 2n = 48). The embryonic development showed that the hatching rate of the hybrid embryos was the highest at 24 degrees C, with 35.75% of embryos hatching normally. A polymerase chain reaction (PCR) with specific primers (5S-F/-R) was used to distinguish LCP from their parents (LC and LP). Results indicate that LCP was hybrids with a hybrid genome that originated from original parents. Based on the chromosome number, LCP was a diploid hybrid fish with 48 chromosomes (2n = 48). Histological observations of the gonads revealed that both female and male LCP individuals developed normally and were potentially fertile. The analysis of mitochondrial genes showed that the late elimination and transcriptional silencing of paternal mitochondrial genome (mtDNA) may occur in hybrid progenies. The paternal mitochondrial gene of cox/ was detected at the blastula and tail bud stages, diminished at the heart-beating stage, then completely disappeared. This suggests that late elimination leads to mitochondrial heteroplasmy. The transcriptional status showed that cox/ mRNA was not detected at any of the stages examined in hybrid progenies, indicating that the paternal mtDNA may have been transcriptionally silenced and the influence on phenotype during embryonic development may have been excluded. This study provides basis for the establishment of diploid hybrid fish as a new germplasm resource, which in turn, can promote the formation of a new hybrid fish line and contribute in future fish genetic breeding.