Hatchery-reared Japanese eel Anguilla japonica larvae ingest various organic matter formed as part of marine snow

Abstract

We observed the feeding incidence of Japanese eel Anguilla japonica larvae of 5-28 days post-hatch (dph) using various organic matter formed as part of marine snow. Food organisms such as microalgae (Rhodomonas sp., Isochrysis galbana, Cyclotella sp., and Chaetoceros calcitrans) and appendicularian Oikopleura dioica were raised as the primary food source of marine snow. In algal feeding trials, 10-28 day-old eel larvae ingested algal cells and transparent exopolymer particles (TEP) produced during the exponential growth phase. Furthermore, the feeding incidence of the larvae showed an increasing trend within the range of 40-100% with larval age (dph) and algal cell concentration. In appendicularian feeding trials, 9-day-old eel larvae ingested a larval tadpole body and abandoned house wreckage. The aforementioned gel-like particles were excreted smoothly out of the end of the mid-hind gut during observation. These results indicate that hatchery-reared Japanese eel larvae ingest organic matter formed as part of marine snow as well as natural eel larvae. The gelatinous substances from microalgae and appendicularian may be available as initial food sources for Japanese eel larvae because of their physical properties (buoyancy, suspensibility, absorption, aggregability, and foexibility) in seawater.