For grading in vats or tanks, floating grader boxes or baskets work well. Fish are dipped into the graders and are retained or pass into other graders or the tank. A simple method to grade fingerlings uses a series of two, three or four grading boxes that nest inside each other. There should be enough space be-tween boxes to accumulate 10 to 30 pounds of fish of a similar size. The nested boxes are put in the tank, and ungraded fish are dipped or poured into the inner box.
Fish pass through the different meshes until they can no longer pass.
The smallest sized fish may be collected outside the outer box. Splashing inside the grader box speeds grading time. Minnows grade faster when thumping sounds are made on the water surface by snapping the fingers. The loading rate of fish in a grader box should not exceed 5 pounds per cubic foot of water. When using a sorting table, a thin sheet of water should be kept on the surface for easy movement of fish.