The book of dragons

Skrill

A jolt from the Strike Class, this Dragon is among the most feared Dragons. They can summon lightning to shoot electrical blasts. Quite a shock!
Enemies Beware! The spiny Skrill attacks with balls of lightning more powerful than any natural storm. the Skrill is aggressive, powerful, and nearly untrainable.
Skrills do not breathe fire. Instead, they channel lightning down their metallic spines, firing it from their mouths in a shower of destructive blasts. They can also store this electrical power in their bodies an release it later on. Because of this unique firepower, Skrills tend to gravitate towards stormy weather. If you find yourself flying through a thunderstorm, watch out! Skrills are also tough. They can take a lot of damage in battle, and give as good as they get. However, the Skrill has one weakness...it cannot fire its lightning from the water. Force a Skrill into the ocean, and it loses the upper hand.
They can hibernate in icy glaciers for decades at a time, and emerge as fierce as the day they were frozen. The skrill is very difficult to train however if you show that your not a threat and appeal to it's better nature they can become quite calm and loyal this dragon doesn't like to be in cages or enslave so freeing them is a good way to earn it's trust which is how Thora manage to tame her trusty skrill strike.
( I don't own thora or strike they are owned by Elise Lowing on fanfiction.net)