Abstract: An apparatus for grading crayfish is provided, comprising a tank having a bottom and sides forming a cavity which will hold water; and a grate assembly having multiple, vertically separated tiers to form spaces between adjacent tiers of sufficient size to accommodate a pre-determined amount of crayfish of pre-determined size. Each tier comprises multiple, horizontally separated round bars, the spacing between the bars in each succeeding lower tier being less than the spacing in the upper tiers. A process for grading crayfish of multiple sizes is also provided, comprising the steps of loading crayfish onto a top tier of a grate assembly of the type described above positioned in a water-filled tank, lifting the grate assembly from the tank after a period sufficient in time to allow all crayfish to seek the lowest level tier achievable in accordance with their size, and removing all crayfish located between one set of adjacent tiers separately from crayfish located between any other set of adjacent tiers.