Vertical distribution and initial food during the planktonic period of larval Isaza goby Gymnogobius isaza

Abstract

　The stock of the Isaza goby Gymnogobius isaza is known to fluctuate greatly. Because initial recruitment is considered to have a high impact on stock fluctuations, it is important to understand the spatial distribution patterns of Isaza larvae. We conducted towing net surveys at variable depths to clarify the vertical distribution of the larvae. Preflexion Isaza larvae were distributed in the lower water temperature range (10-15℃) regardless of depth, whereas flexion larvae thereafter were distributed under the thermocline. Polyarthra spp. were confirmed as the initial food source of the larvae, in addition to copepod nauplii (previously reported). Flexion (and thereafter) larvae preyed mainly on Eodiaptomus japonicus. The study suggested that Isaza larvae change their feeding preference, associated with habitat change and ontogenetic development in feeding functions.