Banggai cardinalfish, Pterapogon kauderni, are native to Indonesia. Since they’re popular in the aquarium trade, they’ve been captured in the wild and are now an endangered species.
They are often found in groups in shallow lagoons. They’re rather sedentary, feeding mostly on plankton in the water currents. Their limited movement prevents them from spreading to other geographic locations, putting them at an even higher risk of extinction.
Another reason they’re endangered is their low fecundity; unlike most marine fish, they only produce a small number of eggs, which the males incubate in their mouths. This isn’t the case for sea hares, of course, which lay millions of eggs apiece, most of which get eaten by other animals.