Trollers, this is your section.
Families: Scombridae (Mackerels and Tunas), Xiphiidae (Swordfishes), Istiophoridae (Marlins)
Common Examples: Blue Marlin, White Marlin, Yellowfin Tuna, Bluefin Tuna, Spanish Mackerel, Kingfish
Ecological Description: BUILT FOR SPEED! These thin, crescent-shaped caudal fins allow for great speed over long distances and are most often seen on fishes that live in open water. The thin fin allows less drag at the posterior end of the fish, which allows for fast-paced, long-distance swimming. Most fish that possess a lunate caudal fin are highly migratory species. These lunate caudal fins do not allow for high maneuverability, and thus, these fishes are almost exclusively piscivorous (fish eating). I should note that the prey items sought by these fishes also possess lunate caudal fins, and are equally as ill equipped at tight maneuvering, so you can imagine an arrow-straight pursuit of predator and prey during a feeding scenario. That’s why straight trolling is such an effective technique for catching these species. That’s a pretty neat example of an evolutionary arms race. Speed kills…literally.
There are always exceptions to the rule, and when it comes to caudal fins there some interesting deviation from these general classifications and their respective ecological descriptions. For instance, permit have a forked-lunate caudal fin, however, their primary prey sources are bottom-dwelling crustaceans. This is contrary to other forked caudal fin species listed, as they primarily feed in open water. These hybrid caudal fins, and those species that deviate from the general rule are truly the most interesting. Can you think of any examples of fishes that deviate from their classification? Can you think of any hybrid caudal fin types?
A final thought. I referred to the term ‘evolutionary arms race’ while discussing the fact that prey items of fishes possessing lunate caudal fins most always have the same caudal fin themselves. The evolutionary arms race plays out most notably in pelagic fishes, but, to some degree, you can see this evolutionary arms race playing out in every group that we have discussed. For instance, many schooling fishes that Tarpon prey upon also have a forked caudal fin. Can you think of anywhere else that this evolutionary arms race might play out?
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Taylor – Founder of Boca Chica Baits