To provide an aquarium for aquarium fish having high heat retention property which does not give stress due to frequent change of water temperature to ornamental fish to be reared. In an aquarium made of transparent glass or transparent acrylic resin, A heat insulating wall 3 formed by sequentially laminating a heat insulating paint layer 31, a foamed urethane foam layer 33 and a foamed polypropylene sheet layer 35 from the water tank surface side is provided on three side walls and the bottom surface excluding the window portion, and the upper opening of the water tank main body 11 Since the lid 2 having the heat insulating structure fitted to the surface is provided, the heat retaining effect is extremely high, the change of the water temperature becomes gentle, and the stress due to the change of the water temperature against the small fish is reduced. (FIG.【課題】飼育する観賞魚に頻繁な水温の変化によるストレスを与えない保温性の高い観賞魚用水槽を提供する【解決手段】透明ガラス製又は透明アクリル樹脂製水槽において、水槽の前面の観賞用窓部を除く三方の側壁と底面に、水槽面側から断熱塗料層31、発泡ウレタンフォーム層33および発泡ポリプロピレンシート層35を順次積層してなる断熱壁3を設けると共に、水槽本体11の上部開放面に嵌合する断熱構造を有する蓋2を設けているので、保温効果が極めて高く、水温の変化が緩やかになり、小型魚に対する水温の変化によるストレスを低減する。【選択図】図3
