A submersion tank for on-board brine freezing of whole or nearly whole fish, and a method for freezing fish employing such tank. One or more pivotable screen baskets are provided in tank containing refrigerated brine. The pivotable screen baskets are provided in a normal, fish receiving position immersed in refrigerated brine. Once fish are frozen, the pivotable screen baskets are pivoted upward to a fish unloading position for delivery of frozen fish for bagging and storage.