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How do spiny dorsal fins help many perciform fishes defend themselves?

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Bluefin tuna swimming underwater in a group, with silvery bodies and streamlined shapes, near Japan. — perciform Bluefin tuna (*Thunnus thynnus orientalis*) in the waters near Japan.

Spiny dorsal fins in many perciform fishes are primarily evolved as a mechanism for defense. These spines, which typically support the first part of the dorsal fin, provide a physical deterrent against predators.1

In addition to their structural role, some perciform species have enhanced this defensive capability by associating these spines with venom glands. For example, the dorsal spines of weever fishes are grooved and connected to venom-secreting structures, which can cause significant pain to potential threats. Similarly, other species, such as dragonets and surgeonfishes, possess specialized venom-bearing structures that serve as effective protection. By combining physical sharpness with chemical defenses, these fishes are better equipped to survive encounters with predators in their environments.21