Ingestion by Japanese Eel Anguilla japonica Larvae on Various Minute Zooplanktons

Abstract

We observed the feeding incidence of Japanese eel Anguilla japonica larvae of 6, 7, 8 and 14 days after hatching (DAH) using various minute zooplanktons such as roti- fer (Proales similis, Synchaeta sp., Keratella sp., Brachionus rotundiformis, B. angularis) and nauplii of copepod Paracyclopina nana, and compared those results to slurry type diets (i.e., shark eggs for control) to evaluate the usability of these planktons as primary food source for the mass culture of eel larvae. Feeding incidence of the larvae on 6, 7 and 8 DAH was 26.7-100% for slurry type diet, 20-46.7% for Proales similis and 0-6.7% for Synchaeta sp. At 14 DAH, feeding incidence of the larvae on slurry type diet and Proales similis reached to 100%, followed by B. rotundiformis (53.3%), Synchaeta sp. (20%), Keratella sp. (13.3%), and B. angularis (6.7%). On this day, slurry type diet (68.9%), Proales similis (37.2%) and Synchaeta sp. (1.0%) were detected in mid-hindgut while the other ingested rotifers remained in foregut of the larvae. These results suggested the possibility of minute illoricate rotifer Proales similis as an initial food source for Japanese eel larvae among the employed zooplanktons.