Graders have been used on fish farms for decades. Separating smaller fish from larger fish can increase feeding efficiency, thereby decreasing production costs. Grading can also limit cannibalism in species where that is common. Intensive grading may occur when the intended market demands a particular size.
The following chart can be used to build inexpensive graders for trout farms. The bars can be constructed from plastic or metal pipe with the frame of the grader made of wood. If plastic pipe is used, a stabilizing bar in the middle may be required to prevent the bars from bending and allowing larger fish to pass through.
| Bar Width | Fish Size | Sample Count | Fish Length in Inches | ||
|---|---|---|---|---|---|
| (inches) | ozs | grams | (#/lb) | C=.0004 | C=.00045 |
| 3/16 | .05 | 1.5 | 312 | 2.0 | 1.9 |
| 1/4 | .10 | 2.8 | 160 | 2.5 | 2.4 |
| 3/8 | .17 | 4.9 | 93.0 | 3.0 | 2.9 |
| 1/2 | 1.0 | 28.4 | 16.0 | 5.4 | 5.2 |
| 9/16 | 1.5 | 42.6 | 10.7 | 6.2 | 5.9 |
| 5/8 | 2.0 | 56.8 | 8.00 | 6.8 | 6.5 |
| 3/4 | 4.0 | 113.5 | 4.00 | 8.5 | 8.2 |
| 7/8 | 8.0 | 227.0 | 2.00 | 10.8 | 10.4 |
| 1 | 10 | 283.8 | 1.60 | 11.6 | 11.2 |
| 1 1/16 | 12 | 340.5 | 1.33 | 12.3 | 11.9 |
| 1 3/32 | 13 | 368.9 | 1.23 | 12.7 | 12.2 |
| 1 1/8 | 14 | 397.3 | 1.14 | 13.0 | 12.5 |
| 1 3/16 | 16 | 454.0 | 1.00 | 13.6 | 13.0 |
| 1 1/4 | 18 | 510.8 | .89 | 14.1 | 13.6 |
| 1 3/8 | 24 | 681.0 | .67 | 15.5 | 14.9 |
| 1 7/16 | 28 | 794.5 | .57 | 16.4 | 15.7 |
