Blue catfish are round in shape with a flat belly, as they age they frequently develop a distinct hump in front of the dorsal fin. Their anal fin is long and has a straight margin and 30-35 rays of equal length. Their color tends to be shades of blue-gray, although they can take on a silvery appearance. The belly typically fades toward white at the very bottom. Their skin is smooth with no scales and generally free of markings.
Most blues are not sexually mature before reaching 24 inches. They spawn in late spring/early summer when water temperatures reach 75°F. Blues are nesters and prefer cavities in drift piles, logs, undercut banks, rocks, or other such areas. When young these cats pursue a varied diet, but as it grows it tends to eat primarily fish. Blue catfish commonly grow upwards of 40 pounds and weights over 100 pounds have been record.
Blue Catfish in Florida
The following is courtesy of Florida Fish and Wildlife Conservation Commission:
Appearance: Adults have stout bodies with prominently humped backs in front of the dorsal fin. They resemble channel catfish by having deeply forked tails, but are lack the spots and have a longer, straight-edged anal. The back and upper sides are blue to slate gray, and the belly is white.
Habitat: Originally found in the Escambia and Yellow rivers in northwest Florida, they are now also in the Apalachicola and Suwannee. Blues occur in big rivers and in the lower reaches of major tributaries. They prefer clearer, swifter water than other catfish, and are usually found over sand, gravel or rock bottoms.
Behavior: Young blues eat aquatic insects and small fish while larger blues prefer crayfish, mussels and other fish.
State Record: 61.5 lbs. Big Catch: 34 inches or 20 lbs.