There are two Dorsal fins on a perch. The anterior and posterior Dorsal fins.
Porpoises have triangular dorsal fins (as opposed to the curved dorsal fins of dolphins and whales). Some species of porpoise have small bumps on their fins, but the purpose of these bumps is unknown.
A survey documented wild males orcas have fins bent. No one is exactly sure why the dorsal fins of killer whales bend, but it may have to do with genetics, injuries, or because the fins can be taller than many humans without any hard bones or muscles for support.
Sharks have straight dorsal fins, dolphins have curved dorsal fins and whales don't have dorsal fins :)
Yes, giant cat fish do have dorsal fins.
Angelfish release gas with their fins.
Yes, shark dorsal fins are triangular and straight while dolphin dorsal fins are very curved and streamlined. A Google Image Search will clarify this even better.
dorsal fins
no
An angelfish!
By its fins
Pectoral fins, dorsal fin, and the flukes!