Earlier in the semester we visited the Honolulu Fish Auction down by the Pier. We a handful of species there in the hundreds, laid out in endless rows. It was interesting to see individual fish, a couple hundred pounds, so still and out of their environment. One of the things that stuck out the most was the size variation of the Yellowfin and Big-Eye Tuna (Ahi). The Ahi instantly came across as extremely strong and swift swimmers. It is known that these tuna can sprint to speeds up to over twenty miles per hour. Obviously, we learned a few things that day.
Our Lab leader pointed out how fish adaptations that have evolved that allow fish to swim at great speeds. Many of these adaptations are geared to reduce pressure drag and to help maintain laminar flow around themselves while swimming. Some of the most visible adaptations include the side indentations for the fins to tuck into. Another obvious adaptation are the recognizable yellow fins on the tail-end sides of the fish. Their purpose is to reduce eddies and turbulent flow.
Perhaps the most interesting feature I learned that day was that the dorsal fin of the Ahi has it’s own pocket to slip into and completely disappear. Evolution has dictated that to reduce just a little more pressure drag from the dorsal fin instead of just tucking away and protruding out ever so slightly, this advantage warranted evolving it’s own pocket. Note that in the following video that the entire fin disappears out of view and that when retracted, one would not be able to tell where the slit begins and ends. An evolutionary adaptations that seems to be so unnecessary may be so much more advantageous to Tuna than our intuition might suggest.