Three types of mackerel, Scomber species, the typical spotted, non-spotted and their intermediate types collected from three locations in the adjacent waters of Japan were analyzed by starch gel electrophoresis and examined for some morphometric and meristic characters. Clear genetic differences between the typical spotted and non-spotted were observed at six loci, i.e. αGpd-B, Idh-A, Ldh-A, Sod, Hem-1 and Hem-2, out of the 23 loci examined. The intermediate individuals genetically belong to either the spotted or non-spotted type and a genetical hybrid possessing both kinds of allele from the two typical types was not observed at all. These three types could be divided into two groups. Average genetic distances for intra- or inter groups were estimated as 0.006 and 0.414, respectively. Two morphological characters, the length of separated anal spine and the number of interneurai spines associated with the first dorsal fin spine, were found to be significant character separating the two groups. From the above results, the two groups of mackerel were clearly divided into two separate species, Scomber australasicus and S. japonicus.
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