Metabolism of hyaluronic acid during early development of the Japanese eel, Anguilla japonica.

Hyaluronic acids (hyaluronans, HAs) are glycosaminoglycans produced in the bodies of Anguilliforme and Elopiforme leptocephali, and HA is thought to serve as a metabolic energy source during planktonic life-stages. To examine this hypothesis, we investigated the dynamics of HA during early growth of the Japanese eel (Anguilla japonica), including during metamorphosis. From histochemical observations in the fully grown leptocephalus, HA occupied approximately 40-50% of the cross-sectional area and muscle tissue occupied less than 20%. However, the HA and water content are at a maximum during leptocephalus, decreasing during metamorphosis. We found that during leptocephalus, HA is actively accumulated in the body and plays a role in specific density adjustment, facilitating planktonic life. It was thought that after metamorphosis the role of HA in facilitating floating would end, and it would be metabolized to glucose and/or triglyceride.