The grader is put in the top of the tank and fish are crowded down toward the tail screen. Fish too large to pass through the bars remain at the bottom of the tank, where they can be moved to another tank with fish of a similar size. The smaller fish swim through the bars and remain in the same tank, although 10 percent or more usually remain behind the grader. This method works best with fish larger than 2 to 3 inches long. Grading fish smaller than this is usually not necessary and will be stressful for the fish.
Mechanized graders are available, and function by pumping the fish onto a series of grading bars.
These systems are very effective when properly sized for the fish to be graded, but are difficult to justify economically for most smaller trout farms. Inventory Fish in each tank on the farm should be sample counted at least monthlyto assure that the fish are growing asexpected and to keep track of loading rates. Feeding according to a feeding rate chart allows you to check daily ration amounts and adjust them as necessary. When sample counting, the fish should be crowded starting from two-thirds of the way down the length of the tank and moving toward the head of the tank. The smallest, weakest fish, which will linger toward the tail of the tank are not representative of the general fish population and will be left be-hind.