How to Accurately Measure Fish?

November 5, 2009

Question: Can you please describe the legal and proper way to measure a fish, particularly largemouth bass? Is it with an open mouth, closed mouth, fanned tail or pinched tail? I would appreciate some fish measuring guidelines to determine whether a catch is legal. Thank you. (Rick B.)

Answer: The first rule when measuring fish is to lay the fish flat on its side and always pinch the mouth closed. All freshwater fish, including largemouth bass, are measured to total length. This is the longest straight-line distance from the tip of the head to the end of the longest lobe of the tail (CCR Section 1.62). The most accurate method is to place the fish’s snout against a perpendicular surface and then measure along the intersecting horizontal surface to the end of the tail. Don’t measure using a flexible “tape” over the fish itself or you will be given a longer false reading. All freshwater fish with a minimum size limit are measured this way.

On the ocean side, most saltwater fish with minimum size limits are measured to total length, but there are some that are measured to fork length instead (e.g. bonito, albacore, barracuda and yellowtail). Fork length is the straight-line distance from the tip of the head to the center of the tail fin (CCR Section 1.62). So again, lay the fish flat on its side, pinch the mouth closed and take your measurement from the tip of the head to the center of the fork of the tail. These are the only two measurements that you will need to know for the purposes of the regulations when measuring whole fish.