DORSAL FIN(S)
the unpaired fin(s) on the midline of the back. Also called the notopterygium. In Pleuronectiformes it is on the opposite side to the anus. In Centriscidae the hind end of the fish has been rotated under the fish so the dorsal fin is on the under surface. Abbreviated as D, D1, D2, or D3 respectively for the only, first, second or third dorsal fins (or their rays and spines). It functions to prevent rolling