Dietary supplementation with chitin hydrolysates for Anguilla japonica leptocephali

This study assessed the effects of diets supplemented with different types of chitin hydrolysate on larval growth of the Japanese eel Anguilla japonica . Larvae were reared for 26 days on artificial diets containing 2% of purified monomeric N -acetylglucosamine (NAG1), a mixture of mono-, di- and trimers (NAG3), a mixture of mono-, di-, tri-, tetra-, penta- and hexamers (NAG6), or a control diet. The larvae fed NAG3 and NAG6 grew significantly more rapidly than the control larvae ( p < 0.05). However, the survival rate of the NAG6-fed larvae was low (8%) for unknown reasons, whereas the survival rates of the NAG1 and NAG3-fed larvae were similar to that of control larvae, about 46% ( p > 0.9). These results indicate that NAG3 is the most effective supplement for eel larvae. A dose–response analysis showed that the optimal level of NAG3 in the diet was around 1%. Although the biological activity of chitin hydrolysates in eel larvae remains unclear, part of these hydrolysates are likely utilized by eel larvae as components of glycosaminoglycan, a major constituent of their bodies. Alternatively, the hydrolysates may act as a bioactive substance, influencing fish health, or in the effective utilization of energy in eel larvae, enhancing their growth.