Early Developmental And Cytogenetic Analysis Of The First Generation Hybrids And Backcrosses Of Paralichthys Olivaceu And Paralichthys Dentatus

Hybridization is the most widely and effective method in the aquaculture breeding. Based on the hybridization and backcross experiments between Japanese flounder (Paralichthys olivaceus) and summer flounder (P. dentatus), early development biology and cytogenetic were employed to characterize inheritance characterizations in these hybrid and backcross offspring. The results are as following:1. The early development of the reciprocal hybrids and two backcross between P. olivaceus)(Po) and P. dentatus(Pd) from fertilization to 64dph were studied. The reciprocal hybrids showed different viabilities. Specifically, the hybrids of P. olivaceus female and P. dentatus male were found to be viable, while the reciprocal hybrids from P. dentatus female and P. olivaceus male were completely inviable. The morphology and distribution of the melanophores of Po×Po, Pd×Po and F1×Po belonged to one pattern, while, Pd×Pd, Po×Pd and F1×Pd belonged to another, which indicated a typical paternal inheritance. Fertilization rates, hatching rates and growth tendency were calculated among the six crosses. The hybrid cross Po×Pd were significantly better compared to Pd×Po, but no significant differences were found when compared with their parent controls.2. The morphology of gametes and fertilization biology of P. olivaceus, P. dentatus and their hybridization were examined. The comparison of egg ultrastructure among Po, Pd and F1 showed the morphology of micropyle region and the distribution density of pores were species-specific. The comparison of spermatozoan ultrastructure revealed Po and Pd were closely related. Cytologically, the six crosses obeyed normal fertilization and cleavage process, and only one male pronucleus was observed in one fertilized egg. Analysis of the time distribution from fertilization to the first cleavage revealed an obvious"delay"at pronucleus fuse in the cross of Pd×Po. We speculated the"delay"might implicate to some extent the cytoplasmic-nuclear incompatibility occurred during the process of fertilization.3. The chromosome analysis, NOR banding and DAPI banding distribution were analyzed in P. olivaceus, P. dentatus and their reciprocal hybrids chromosomes. The chromosome analysis showed that Po×Pd had the same chromosome number as parents'. However, two chromosomes were missing in Pd×Po offspring indicating that the latter were aneuploids. Silver staining revealed that the number of NORs was two and located on different chromosomes in different crosses, which could be used to differentiate each cross. The pattern of DAPI banding mainly distributed at telomeric regions.4. Chromosomal localization of 18S rDNA, 5S rDNA and vertebrate telomeric sequences were analyzed in P. olivaceus, P. dentatus and their reciprocal hybrids chromosomes. 18S rDNA and 5S rDNA was assigned to two loci in P. olivaceus, P. dentatus and their reciprocal hybrids. 18S rDNA was assigned to different chromosomes in P. olivaceus, P. dentatus and their reciprocal hybrids, the locus and number were accordance with silver staining, which could also be used to differentiate each cross. Vertebrate telomeric sequences, detected by FISH, were located on both ends of each chromosome of P. olivaceus, P. dentatus and their reciprocal hybrids. Interstitial signal was observed on some chromosomes. The signal intensity varied among different chromosomes.