Slide thicknesses for different types of fish scales

0.50 mm (0.020”) = Trout, salmon, tullibee
0.76 mm (0.030”) = Young fish – many species
1.00 mm (0.040”) = Bass, walleye, perch, sucker, sunfish
1.50 mm (0.060”) = Carp

Tips for taking scale samples:
Age determination of fish is easy if you are consistent. Take scale samples from a specific part of each fish. (a) On spiny-rayed fish, just below the lateral line and below the middle of the spiny dorsal fin. (b) For most soft-rayed fishes, the area between the lateral line and dorsal fin. (c) For trout, the area directly below the lateral line beneath the posterior end of the dorsal fin is best.