Analysis of the early development in first and backcross generations between paralichthys olivaceus and paralichthys dentatus

This study investigated the performance difference of reciprocal hybrids and backcrosses between Paralichthys olivaceus and Paralichthys dentatus. The fertilization and hatching rates, combined fitness measure, early developmental characteristics and chromosome number were analyzed. The crosses of P. olivaceus female x P. dentatus male (F1), F1 female x P. olivaceus male and F1 female x P. dentatus male could normally fertilize (the fertilization rate: 93.2 to 97.7%), hatch (the hatching rate: 84.4 to 93.1%) and develop during pre-larvae stage. However, the fertilization rate (41.7%) and combined fitness measure (0.327) of P. dentatus female x P. olivaceus male was significantly reduced compared with other crosses. And the embryos of P. dentatus female x P. olivaceus male hatched out with flexural spine and poor vitality and died within 3 days post hatching. In addition, the result of cytogenetics analysis showed two chromosomes were missing in P. dentatus female x P. olivaceus male, which provided evidence of postzygotic barriers in the two species. The results would be useful for better understanding the genetic phenomena of the distant hybridization in fish species.