To provide a water tank capable of upbringing fish effectively.SOLUTION: A loop type water tank 1 has a first circular water tank part 10, a second circular water tank part 20 and a connection part 30 for connecting these water tank parts 10, 20. The connection part 30 includes a first connection flow path 31 for connecting a first end 11 of the first circular water tank part 10 to a first end 21 of the second circular water tank part 20, and a second connection flow path 32 for connecting a second end 12 of the first circular water tank part 10 to a second end 21 of the second circular water tank part 20, and the second connection flow path 32 exists under the first connection flow path 31.SELECTED DRAWING: Figure 1【課題】魚類を効果的に育成できる水槽を提供する。【解決手段】ループ型水槽１は，第１の円形状水槽部１０と，第２の円形状水槽部２０と，これらの水槽部１０，２０を接続する接続部３０とを有する。接続部３０は，第１の円形状水槽部１０の第１の端部１１と，第２の円形状水槽部２０の第１の端部２１とを接続する第１の接続流路３１と，第１の円形状水槽部１０の第２の端部１２と，第２の円形状水槽部２０の第２の端部２１とを接続する第２の接続流路３２とを含み，第１の接続流路３１の下部に第２の接続流路３２が存在している。【選択図】図１
