PROBLEM TO BE SOLVED: To provide a composition for controlling microsporidia in fish and shellfish which prevents infection of fish and shellfish muscle or organs with microsporidia and/or inhibits the proliferation of microsporidia in fish and shellfish muscle or organs and/or improves the effect of eradicating microsporidia inside fish and shellfish, as well as having excellent safety, and a method of controlling microsporidia in fish and shellfish using the same.SOLUTION: A composition for controlling microsporidia in fish and shellfish consists of one or more compounds as an active ingredient selected from: a compound represented by formula (I)； a pharmaceutically acceptable salt thereof； and a compound metabolized in the body of fish and shellfish to produce the compound represented by formula (I). (Ris an amino group, an aminocarboxylic acid ester group, a methineaminyl group, a methylsulfanyl group, etc.； Ris an amino group, an aminocarboxylic acid ester group, an alkoxy group, a thioalkyl group, an acyl group, etc.； and R, Rand Rare each independently, H, a halogen, a nitro group, a carboxyl group, an alkyl group, an aryl group, etc.)SELECTED DRAWING: None【課題】魚介類の筋肉又は臓器への微胞子虫の感染を予防及び／又は魚介類の筋肉又は臓器中での微胞子虫の増殖を抑制及／又は魚介類の体内から微胞子虫を駆除する効果が高く、安全性にも優れた魚介類の微胞子虫の防除用組成物及びそれを用いた魚介類の微胞子虫の防除方法の提供。【解決手段】式（Ｉ）で表される化合物、その薬学的に許容される塩及び魚介類の体内での代謝により式（Ｉ）で表される化合物を生成する化合物から選択される１又は複数の化合物を有効成分として含む魚介類の微胞子虫の防除用組成物。［Ｒ２はアミノ基、アミノカルボン酸エフテル基、メチンアミニル基、メチルスルファニル基、等；Ｒ５はアミノ基、アミノカルボ酸エステル基、アルコキル基、チオアルキル基、アシル基等；；Ｒ４、Ｒ６及びＲ７は各々独立にＨ、ハロゲン、ニトロ基、カルボキル基、アルキル基、アリール基等］【選択図】なし
