Dorsal fin

argosies set sail
we’ve bounty to capture
and lands to defend!

I saw my first ocean sunfish while visiting Valencia’s Oceanogràfic and giggled. How silly that this fish’s pectoral fins look like ears. Where did this beast’s caudal fin go? Why, the anal fin is symmetrical to the dorsal fin protruding from its back!

For most fishes the dorsal fin helps stabilize the animal so it doesn’t somersault endlessly through water.

The dorsal fin of Mola mola is dual purpose; balance and boost. Without a proper caudal fin these basking beauties must rely on waving their dorsal (and anal) fin to achieve forward momentum while exploring Earth’s oceans.

Sailfish (Istiophorus spp.) dorsal fins are pretty extraordinary too. When hunger strikes sailfish erect their massive dorsal fin (which basically runs the length of their 3 m bodies) and launch at schools of small fish. Imagine how confused you would be if dozens of shower curtains charged at you from all angles. The frazzled prey fish crowd into a swirling mass called a baitball. Sailfish take turns striking at the baitball to satisfy their appetites.

How about that billowing cape on Arctic grayling (Thymallus arcticus)? Their characteristically bespeckled and multicoloured dorsal fin is rather exquisite. Both males and females raise their dorsal fin tall to threaten other grayling that may be creeping too close to home (i.e. 1 mof gravel in an Arctic stream). Males are also observed draping their dorsal fins over the backs of females during spawning; possibly keeping a female close from other suitors or perhaps an affectionate side-hug.