Leptocephalus larvae collected from the western North Pacific Ocean were identified as Gymnothorax buroensis (Bleeker, 1857), Gymnothorax meleagris (Show, 1795), Gymnothorax eurostus (Abbott, 1860), and Gymnothorax pseudothyrsoideus (Bleeker, 1853) on the
basis of morphometric and mitochondrial DNA sequence analyses. The larvae were characterized respectively by counts of 110–115, 125–128, 124–128, and 128–134 total myomeres; 63–67, 77–78, 64–67, and 80–83 preanal myomeres, and 56–60, 67–68,
59–66, and 73–74 last vertical blood vessel myomeres. The first three species share a common melanophore pattern of a horizontally elongate group of relatively large and/or small irregular melanophores before and behind the eye, with the larvae of G. buroensis also having
similar melanophores on the dorsal surface of the head and brain. Unlike the other species, larvae of G. pseudothyrsoideus had minute melanophores distributed over much of the head and body. Diagnostic morphological characters of the leptocephalus larvae were described for the four
Gymnothorax species; these characters may enable species level identifications without DNA analysis.
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