SPINY-RAYED DORSAL FINS This is one of the most important pages in the key, used to separate out two major groups of fish – those that have a spiny-rayed dorsal fin, and those that don’t. Spiny-rayed fishes often keep their spiny dorsal folded down unless they are disturbed. This can make it hard to see. Smallmouth and largemouth bass, silversides, and bluefish are among the species that do this. Also, the spiny dorsal fin might be very small, as it is on the oyster toadfish.
Examine the fish especially closely if the dorsal fin on your fish is set well back towards the tail; there may be a spiny dorsal fin in front of it. It may require a bit of gentle poking and handling to get the fish to display its spiny dorsal, which may pop up for just a second or two. Be patient and careful in your examination.