In GPC molecular weight analysis using a UV detector, a low molecular weight lignin having a molecular weight peak at a wavelength of 254 nm and / or a molecular weight having a molecular weight in the range of 10,000 to 40,000 at a wavelength of 254 nm An aquatic product growth promoter comprising lignin as an active ingredient. [Selection figure] NoneＵＶ検出器を用いたＧＰＣ分子量分析において、波長２５４ｎｍにおける分子量ピークを、分子量４，０００～９，５００の範囲に有する低分子リグニンおよび／または分子量１０，０００～４０，０００の範囲に有する高分子リグニンを有効成分とする、水産生物成長促進剤。【選択図】なし
