The invention is a land-based fish rearing plant comprising: a postsmolt unit (A) with the following features: - an oval flow tank (1A) for postsmolt, subdivided for postsmolt cohorts of successively increasing sizes, - at flow generator (9A) for providing a main flow (OAmain), - water outlets (7A) for a partial flow from the oval flow tank (1A) to a water treatment plant (4A) wherein said water treatment plant (4A) is arranged within the perimeter of an inner wall (lOAi) of said flow tank (1A), at least two grow-out units (B, C) for growing salmon in the stages after the postsmolt stages, each grow-out unit (B, C) comprising: - an oval flow tank (IB, 1C) for said growing salmon, subdivided into tank sections (3B1 to 3Bm, 3C1 to 3Cm) for growing salmon cohorts of successively increasing sizes, - a main flow generator (9B, 9C) for providing a main flow (OBmain, OCmain), - water outlets (7B, 7C) for a partial flow from the oval flow tank (IB, 1C) to a water treatment plant (4B, 4C) comprising and a water return inlet (8B, 8C) to said flow tank (IB, 1C), - wherein said water treatment plant (4B, 4C) is arranged within the perimeter of an inner wall (lOBi, lOCi) of said flow tank (IB, 1C) a purge-unit (12) comprising, arranged between said grow- out units (B, C), wherein the last sections (m) in said grow-out units (B, C) are connected via lock-gates (14B, 14C) to an inlet channel (15) to two or more purge chambers (13a, 13b,... 13z) for temporary holding and purging of the salmon prior to its slaughtering, wherein the purge-unit (12) comprises at least a water treatment plant (16) and an export line (171) to a fish slaughterhouse (17).
