Atsushi Tawa

Identification of aquarium-raised muraenid leptocephali, Gymnothorax minor

Leptocephalus larvae of Gymnothorax minor collected from eastern Kyushu were identified by observation of metamorphosis procedure. The leptocephali were characterized by 135–142 total myomeres (31–42 predorsal, 87–95 preanal) and the last vertical blood vessel between myomeres 77–85. Diagnostic pigments were apparent on the head, the somatic (below intestine) and splanchnic (along pronephric ducts) regions, before the dorsal fin origin, ventrally on the spinal cord, and along the dorsal and anal fin bases. Such pigments were suitable for species identification of metamorphosing larvae because of their persistence during that process.

Larval identification following metamorphosis in the slender brown moray Strophidon ui from the western North Pacific

Leptocephalus larvae collected from the western North Pacific, and characterized by yellow head pigmentation and many myomeres, were identified as the slender brown moray Strophidon ui following observations of metamorphosis in an aquarium. The leptocephali had 184–196 total myomeres (84–90 predorsal, 116–122 preanal) and 95–102 last vertical blood vessel myomeres. A horizontally elongate group of irregular melanophores before and behind the eye formed a poorly defined band. Some irregular melanophores on the iris encircled the pupil, and minute melanophores occurred ventrally on the spinal cord and along the dorsal and anal fin bases. Yellow pigments were present in anterior and posterior regions adjacent to the eye in fresh specimens. It was possible to clearly distinguish the leptocephali of S. ui from six unassigned leptocephalus types and Gymnothorax minor reported previously from the same region, owing to the lower total myomere counts (106–142) in the latter. This is the second description of specifically identified muraenid leptocephali from the western North Pacific.

Identification of leptocephalus larvae of the tiger moray Scuticaria tigrina (Anguilliformes; Muraenidae) based on morphometric and genetic evidence

Leptocephali collected from the south of Japan and assigned to the muraenid subfamily Uropterygiinae were identified as Scuticaria tigrina on the basis of morphometric and genetic evidence. Significant meristic counts included: total myomeres (TM) 166–172, last vertical blood vessel myomeres 121–126, preanal myomeres 139–145 and predorsal myomeres 157–158. Melanophores were apparent on the posteroventral surface of the brain and about the first myomere on the upper opercular region, along the ventral midline from the gallbladder to the anus, the ventral aspect of the spinal cord and the ventral midline from the anus to the origin of the anal fin, and on both dorsal and anal fin bases. The leptocephalus of S. tigrina could be easily distinguished from previously reported uropterygiine leptocephali because of the high myomere numbers (>160 TM), the unusually long gut and the pigmentation patterns.

Leptocephalus larvae of two moray eels (Anguilliformes; Muraenidae), Gymnothorax sagmacephalus and Gymnothorax albimarginatus, identified from morphometric and genetic evidence

Two forms of muraenid leptocephali, collected from the western Pacific Ocean, were identified as Gymnothorax sagmacephalus Böhlke 1997 and Gymnothorax albimarginatus (Temminck and Schlegel 1846) on the basis of morphometric and genetic analyses. The leptocephali of each species were characterized, respectively, by counts of 172–175 and 186–191 myomeres, 43–44 and 47 predorsal myomeres, 109–113 and 127–134 preanal myomeres, and 100–104 and 118–119 last vertical blood vessel myomeres. Gymnothorax sagmacephalus leptocephali had minute melanophores over much of the head and body, closely resembling the condition in Gymnothorax minor (Temminck and Schlegel 1846), whereas those of G. albimarginatus not only had minute melanophores over much of the head and body, but also a pair of melanophore groups on the posteroventral and posterodorsal aspects of the head. Such groups are here considered to represent highly specific characters. Although a previous opinion postulated that G. sagmacephalus is a juvenile of G. albimarginatus, and the adult morphologies of the two species have a lot in common, they clearly differ in both leptocephalus morphology and genetic sequence. Therefore, G. sagmacephalus was concluded as being a valid species.