Age and growth of Saurenchelys (Nettastomatidae) and Dysomma (Synaphobranchidae) leptocephali in the East China Sea

Abstract

The otolith microstructures of the leptocephali of Saurenchelys stylura and Dysomma sp., collected in November and December 2000 in the East China Sea, were examined to determine their larval ages and growth rates, and the spawning times of these two species of outer shelf and slope marine eels. Leptocephali ranging in size from 8 to 48 mm total length were examined, and the nettastomatid, S. stylura, and the synaphobranchid, Dysomma sp., had estimated ages that ranged from 16 to 75 days and 17 to 66 days, respectively. The overall growth rate of S. stylura was 0·68 mm day−1(n = 21), and of Dysomma sp. was 0·44 mm day−1(n = 22). These growth rates were similar or slightly faster than those observed for anguillid leptocephali in offshore areas of the western Pacific. The backcalculated hatching dates for these two species were from September to November. The otolith increment widths of S. stylura showed an increase before 20 to 30 days that were similar to those in anguillid species, but in Dysomma sp. there were no remarkable increases.