Age and growth of Anguilla interioris leptocephali collected in Indonesian waters

Anguilla interiorisis has been only known to be distributed in northern New Guinea, but recent sampling surveys for leptocephali and the development of species identification techniques using DNA analysis have discovered that this species also appears to occur off Sumatra in the eastern Indian Ocean, and may be present in other areas of the Indonesian Archipelago. To reveal the ages and early life histories of this species, the otolith microstructure of the leptocephali collected near the Sulawesi Island and off Sumatra of Indonesia were examined. The otolith microstructure of the A. interioris leptocephali was similar to other anguillid species and showed narrow increment widths (0.49-0.58μm) near the core that increased (1.14-1.34μm) before decreasing again until the otolith edge (0.51-0.83μm), except in the smallest specimen (12.4mm TL) collected off Sumatra, which had no peak. The range of Sr: Ca ratios in their otoliths were 8.37 to 14.01. Their ages were 19d for the smallest specimen from off Sumatra, 85d for the specimen (48.9mm TL) from Tomini Bay, and 85 to 94d for the three specimens (43.4-46.5mm TL) from the Molucca Sea. The overall growth rate of the leptocephali was 0.48mm/d, and this value was intermediate compared with the growth rates of the other anguillid species. The age of the smallest A. interioris leptocephalus collected off Sumatra and the geographic patterns of currents in the regions, suggest that it was spawned in the Indian Ocean and that it may belong to a different population than the New Guinea population

Correspondence between otolith microstructual changes and early life history events in Anguilla marmorata leptocephali and glass eels

To determine the exact correspondence between otolith characteristics and early life history events such as metamorphosis, coastal migration and recruitment to estuaries, both otolith microstructure and microchemistry analyses were applied to a sequential developmental series of samples, e. g. leptocephali, a metamorphosing larva, oceanic glass eels, and coastal glass eels. Total length and age were 10.1-50.7 mm and 22-137 d in leptocephali, 46.3 mm and 147 d in a metamorphosing larva, 47.8, 48.6 mm and 159, 160 d in oceanic glass eels, and 47.9-54.8 mm and 119-168 d in coastal glass eels. Checks at hatching and first feeding were observed in all specimens, but metamorphosis and freshwater checks were observed only in some specimens. It was confirmed that the abrupt drop in otolith Sr : Ca ratios and drastic increases of otolith increment widths in the metamorphosing larval stage correspond to the onset of metamorphosis, and the decrease after the peaks suggested the completion of metamorphosis, because the metamorphosing larva had no decrease in incremental widths. The relatively conserved Sr : Ca ratios decreased sharply in synchrony with the increasing increment widths. This study provides the first direct evidence that these drastic changes in otolith microstructure and microchemistry actually occur during metamorphosis, which has been only hypothesized

Correspondence between otolith microstructual changes and early life history events in Anguilla marmorata leptocephali and glass eels

To determine the exact correspondence between otolith characteristics and early life history events such as metamorphosis, coastal migration and recruitment to estuaries, both otolith microstructure and microchemistry analyses were applied to a sequential developmental series of samples, e. g. leptocephali, a metamorphosing larva, oceanic glass eels, and coastal glass eels. Total length and age were 10.1-50.7 mm and 22-137 d in leptocephali, 46.3 mm and 147 d in a metamorphosing larva, 47.8, 48.6 mm and 159, 160 d in oceanic glass eels, and 47.9-54.8 mm and 119-168 d in coastal glass eels. Checks at hatching and first feeding were observed in all specimens, but metamorphosis and freshwater checks were observed only in some specimens. It was confirmed that the abrupt drop in otolith Sr : Ca ratios and drastic increases of otolith increment widths in the metamorphosing larval stage correspond to the onset of metamorphosis, and the decrease after the peaks suggested the completion of metamorphosis, because the metamorphosing larva had no decrease in incremental widths. The relatively conserved Sr : Ca ratios decreased sharply in synchrony with the increasing increment widths. This study provides the first direct evidence that these drastic changes in otolith microstructure and microchemistry actually occur during metamorphosis, which has been only hypothesized

Evidence for migration of metamorphosing larvae of Anguilla japonica in the Kuroshio

Two sampling surveys of the R/V Tansei Maru were conducted in the Kuroshio region south of Kyushu Island of Japan and to the south in the western North Pacific, to study the distribution patterns of the larval stages of the Japanese eel Anguilla japonica as they approach their recruitment areas in East Asia. Nine fully-grown premetamorphic leptocephali (49.5-58.3mm TL) were collected during November 1996 to the east of Taiwan. During November and December 2000, nine early stage glass eels (51.3-57.0mm TL, pigmentation stage II-IV) that were still in the late metamorphosis stages were collected in the Kuroshio. These findings suggest that metamorphosing Japanese eel leptocephali that recruit to the northern part of their species range migrate in the Kuroshio. They may detrain from the Kuroshio at the pigmentation stage IV-VA and begin their coastal migration

Age and growth of Anguilla interioris leptocephali collected in Indonesian waters

Anguilla interiorisis has been only known to be distributed in northern New Guinea, but recent sampling surveys for leptocephali and the development of species identification techniques using DNA analysis have discovered that this species also appears to occur off Sumatra in the eastern Indian Ocean, and may be present in other areas of the Indonesian Archipelago. To reveal the ages and early life histories of this species, the otolith microstructure of the leptocephali collected near the Sulawesi Island and off Sumatra of Indonesia were examined. The otolith microstructure of the A. interioris leptocephali was similar to other anguillid species and showed narrow increment widths (0.49-0.58μm) near the core that increased (1.14-1.34μm) before decreasing again until the otolith edge (0.51-0.83μm), except in the smallest specimen (12.4mm TL) collected off Sumatra, which had no peak. The range of Sr: Ca ratios in their otoliths were 8.37 to 14.01. Their ages were 19d for the smallest specimen from off Sumatra, 85d for the specimen (48.9mm TL) from Tomini Bay, and 85 to 94d for the three specimens (43.4-46.5mm TL) from the Molucca Sea. The overall growth rate of the leptocephali was 0.48mm/d, and this value was intermediate compared with the growth rates of the other anguillid species. The age of the smallest A. interioris leptocephalus collected off Sumatra and the geographic patterns of currents in the regions, suggest that it was spawned in the Indian Ocean and that it may belong to a different population than the New Guinea population

Genetic identification of two types of Ariosoma leptocephali

Comparisons of genetic sequences of the mitochondrial DNA 16S rRNA gene were used to match two species of congrid eels of the genus Ariosoma to two established Ariosoma-types of leptocephali. 18 Ariosoma sp. 7 leptocephali (40-151mmTL) were matched with an A. major adult (333mmTL) collected from Tosa Bay of eastern Japan with 0.2-0.7% sequence differences, and 1 Ariosoma sp. 8 leptocephalus (330mmTL) was matched with two A. shiroanago adults (317 and 320mmTL) also from Tosa Bay with no sequence difference. Ariosoma sp. 7 leptocephali have been collected in many regions of the western North Pacific (WNP), and the leptocephali from both the East China Sea and the WNP were matched with A. major, suggesting that the leptocephali of this species are widely distributed in the region. The leptocephali of Ariosoma sp. 8 appear to be much less common in most areas that have been sampled recently

Correspondence between otolith microstructual changes and early life history events in Anguilla marmorata leptocephali and glass eels

To determine the exact correspondence between otolith characteristics and early life history events such as metamorphosis, coastal migration and recruitment to estuaries, both otolith microstructure and microchemistry analyses were applied to a sequential developmental series of samples, e. g. leptocephali, a metamorphosing larva, oceanic glass eels, and coastal glass eels. Total length and age were 10.1-50.7 mm and 22-137 d in leptocephali, 46.3 mm and 147 d in a metamorphosing larva, 47.8, 48.6 mm and 159, 160 d in oceanic glass eels, and 47.9-54.8 mm and 119-168 d in coastal glass eels. Checks at hatching and first feeding were observed in all specimens, but metamorphosis and freshwater checks were observed only in some specimens. It was confirmed that the abrupt drop in otolith Sr : Ca ratios and drastic increases of otolith increment widths in the metamorphosing larval stage correspond to the onset of metamorphosis, and the decrease after the peaks suggested the completion of metamorphosis, because the metamorphosing larva had no decrease in incremental widths. The relatively conserved Sr : Ca ratios decreased sharply in synchrony with the increasing increment widths. This study provides the first direct evidence that these drastic changes in otolith microstructure and microchemistry actually occur during metamorphosis, which has been only hypothesized