Genetic comparison between torafugu Takifugu rubripes and its closely related species karasu Takifugu chinensis


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Abstract:  Sequence analyses of mitochondrial (mt) and nuclear genes were performed for genetic comparison between two Takifugu pufferfish species: torafugu T. rubripes and karasu T.  chinensis. With a sequence coverage of 20% in mtDNA, 640, 308, 344, 522 and 697 bp encoding mt 16S ribosomal RNA (rRNA), adenosine triphosphatase 6 (ATPase 6), nicotinamide adenine dinucleotide dehydrogenase subunit 4 (ND4), ND5 and cytochrome b (cyt b), respectively, among 24 wild torafugu, 24 wild karasu and six hybrid-like samples, 15% of the torafugu identified by external color patterns showed nucleotide sequences consistent with karasu. Meanwhile, sequences of 60% karasu were consistent with those registered for torafugu (AJ421455). As for the hybrid-like samples, two possessed karasu-specific sequences in some base positions while torafugu-specific sequences in others. The remaining hybrid-like samples possessed torafugu-specific sequences. On the other hand, the mt control region did not show such type of consistency. Analysis of nuclear melanocortin receptor genes (MC1R, MC4R) among 54 samples showed 99–100% inter- and intraspecific sequence identity. Partial nuclear 18S rRNA, complete internal transcribed spacer 1 (ITS1), partial 5.8S rRNA and ITS2 genes showed similar levels of identity, indicating a very low level of variation in their respective gene fragments between the two Takifugu species.