Elemental Requirements of Rearing Seawater for Unfed Larvae of the Japanese Eel ( Anguilla japonica Temminck and Schlegel)

This study assessed the influence of salinity and element composition of rearing seawater on unfed Japanese eel ( Anguilla japonica ) larvae at 5 days after hatching (DAH). First, no significant differences in larval survival were found between natural and artificial seawater across various container materials and sizes (50mL–20 L). Subsequently, 10 to 15 larvae were housed in 100m L polypropylene (PP) bottles with seawater of different elemental compositions. Analyses of mean lethal DAH, survival activity index (SAI), and survival rate on the mean lethal DAH demonstrated that Na, Mg, K, and Ca are essential, while S and Cl also appear highly required. Next, optimal salinity (1–34 psu) was investigated by rearing individual larvae in 48‐well microplates, revealing that SAI peaked at 13–16 psu. Formulated seawater containing these six key elements at 13 psu significantly enhanced larval survival. These findings confirm that specific salinity and elemental composition are conducive to Japanese eel larval survival and offer insights for optimizing hatchery protocols.