Aww... It's a cute baby dragon. It hatched with fins instead of legs and did not seem to react well in freshwater, so you placed it in the nearby ocean.
Its dorsal fin has grown larger, and it rarely surfaces anymore. It must be close to maturing.

Young dragons are relatively defenseless. Their scales don't grow in until right before they mature, and they have almost no strength. Once a hatchling's wings grow in, it marks the beginning of maturation. At this point they are usually left alone by their mother and begin to hunt and survive on their own.