Growing to the size of myths and legends, catfish are known to live for over 20 years and reach weights of over 100 lbs. Named for the tactile organs resembling cat whiskers that protrude from the sides their face, more than 40 species of catfish range across North America. As catfish age their fins grow in proportion to the rest of their bodies, with the majority of growth occurring during periods when the fish feed most actively. These growth spurts are used to determine the age of a catfish.
Items you will need
Gloves
Pliers
Micro-tooth saw
Lighted microscope
Wear gloves to protect your hands from the sharp points at the ends of the dorsal fins.
Lay the catfish on its stomach. Grasp the end of one of the catfish's pectoral fins with the pliers. Gently rotate the top of the pectoral fin inward toward the fish with the pliers. Pull back on the fin with slow steady pressure while twisting until the fin detaches from the fish's body.
Return the catfish to the water, if you do not want to keep the fish. Catfish will survive with only one pectoral fin.
Cut the detached fin in half lengthwise with a micro-tooth saw. Move the saw along the fin a few millimeters from the first cut and cut through the fin second time, removing a thin slice of the fin.
Place the slice of fin under a lighted microscope. Adjust the magnification on the scope until you can clearly see the alternating dark growth rings between the white spaces on the piece of fin.
Count the growth rings on the slice of fin, from the center outward. The number of dark rings indicates the number of years the fish has lived. For example, 10 dark rings would indicate the fish has lived for 10 years.