Tidal

Almost all Tidal Class dragons live in ocean, although some of them have amphibian biology allowing them to survive on land. Few of these dragons are cable of creating flames, but many can generate electricity. Dragons of this class are generally larger than those of other classes. Despite this, they are usually very peaceful ocean dwellers who prefer to be left alone and when trained, are exceedingly loyal. According to Hiccup, Tidal Class dragons don't react well to signs of aggression.