Transcriptomics reveals that NAD(P)H affects the development of the Zig-zag eel (Mastacembelus armatus ♀) × Spiny eel (Sinobdella sinensis ♂) hybrid offspring leading to low hatching rates.

Zig-zag eel (Mastacembelus armatus (2 n = 48)) and Spiny eel (Sinobdella sinensis (2 n = 48)) are two species of the Mastacembelidae family commonly found in southern China. Hybridization between the two has a very high deformity rate and a very low hatching rate. In order to investigate the reasons for this, the first hybridization between M. armatus and S. sinensis was carried out using artificial insemination, and the embryonic development of the hybrid offspring was examined using microphotography, and the malformations of the hybrid offspring were investigated by transcriptomics. The experiments showed that the average egg production was 4265.7 ± 322.94 (Mean ± SD), the average fertilization rate of hybrid offspring was 98.67 ± 0.58 % (Mean ± SD), the hatching rate was 12.06 ± 3.44 % (Mean ± SD), the deformity rate was 98.15 ± 3.21 % (Mean ± SD), and the embryonic development successively went through the five main stages of fertilized egg, egg cleavage, embryo formation, organogenesis, and exertion of membranes. Transcriptomics showed that the expression of NAD(P)H-related enzyme activity DEGs was increased, and many DEGs related to cell signaling molecule transmission and metabolic regulation are enriched in KEGG pathways, such as IL-17 signaling pathway, Osteoclast differentiation, TNF signaling pathway and MAPK signaling pathway. etc. The major types of DEGs corresponded to those coding for proteins. This study suggests that the high malformation rate in hybrid offspring may be caused by impaired synthesis of proteins during embryonic development.