Influence of environmental factors on the feeding behavior of reared Japanese eel Anguilla japonica preleptocephali given picocyanobacteria

Artificially reared Japanese eel Anguilla japonica preleptocephali (− 7 mm total length, 6–7 days post-hatch) were fed picocyanobacteria (Synechococcus sp., strain NIES-976), and their food intake was observed via autofluorescence intensity per area of the mid-hindgut, which was used as an index of gut fullness. Time-course observations revealed that the larvae actively fed under light and dark conditions. Food intake was significantly greater in the low-salinity group (50% seawater) than in the control group (100% seawater). Food intake did not differ significantly under photoperiods of 24-h light versus 24-h dark, indicating a light-independent feeding rhythm. A comparison of larval feeding efficiency under high and low cell densities of picocyanobacteria revealed remarkably high intake of the food material by larvae in the high-density food concentration group, indicating density-dependent food ingestion. This specific feeding ecology whereby Japanese eel larvae can efficiently ingest suspended pico-sized food particles from seawater even in complete darkness may enable them to adapt to oligotrophic environments.