The blue marlin adapts to its underwater environment by stinging using it's long snout to stun prey that it's hunting. Blue marlins are also among the fastest of fish, allowing it to swim away from predators.
Clownfish have adapted to their environments by adapting to allow them to live in stinging anemones. They are immune to the painful stings. Clownfish lay their eggs on a nearby rock so they are in sight of both parents, and are easily protected.
The great barracuda has adapted to it's need to hunt other fish by growing sharper and sharper teeth. The great barracuda is also slender, allowing for faster traveling. Not as fast as the blue marlin, but still fast.