Net Mesh Size Selection

Mesh size is the distance between opposite knots or the bar length in knotless netting, chosen so water flows freely through the cage while retaining the fish at their current size. Grow-out Atlantic salmon typically start at 30 mm mesh and step up to 40 to 48 mm or larger as fish pass roughly 1 to 2 kg; a common rule is that mesh perimeter should exceed maximum girth by a safety margin, and escape-tested netting is certified to standards such as NS 9415. The operational consequences are direct: an undersized mesh chokes water exchange, lowers dissolved oxygen inside the pen, accelerates biofouling drag, and increases deformity risk when fish push against the net; an oversized mesh wastes feed through loss, allows predators to reach in, and permits escapes of smaller fish. Mesh selection interacts with grading schedules, because graded fish of uniform size allow a coarser, freer-flowing net. Related concepts include net cleaning frequency, predator netting, and stocking density, all of which shift the effective water exchange the mesh must support.