On the beach the other day I found a dead fish about ten inches long, now turned stiff and white beneath the sun. Finding dead fish there isn't unusual, but two features of this one caused me to pick it up and take a closer look.
First, the fish was densely arrayed with stiff, sharp, toothpick-size spines. Second, its conspicuous teeth were fused together in such a way as to form a beak-like mouth. Seeing the teeth, I could visualize the fish gnawing at something hard like shellfish or even coral.
Googling the keywords "fish, spines, Mexico" I came up with thumbnail pictures leading me to decide that probably I'd found either a Balloonfish, DIODON HOLOCANTHUS, or the very closely related Porcupinefish, DIODON HYSTRIX. Whichever it was, the finding aroused my imagination mightily.
For, I'd seen such spiny fish in underwater nature documentaries, but never had I known the real thing. The ones in the films, when threatened, had suddenly puffed themselves up to form spiny globes few predators would have wanted to tackle. Reading about the behavior of Balloonfish and Porcupinefish, I found that they do the same thing, gulping water when they want to expand. You can read about and see these fish, including a puffed-up one, at http://www.flmnh.ufl.edu/fish/Gallery/Descript/Balloon/Balloon.htm.
That page also tells how these fish use their fused teeth. After spending their days hiding in crevices they prey on snails, sea urchins and hermit crabs by using their teeth to crack open shells.
The species' spines and fused teeth must be a pretty effective combination, for both species are distributed circumtropically -- throughout all the world's tropical seas -- in such environments as mangroves, seagrass beds, and rocky, open bottom areas.
How wonderful to know that right offshore, and not just in documentary films, Balloonfish and Porcupinefish live such exotic lives.