Rottdragons are only mentioned once in the How to Train Your Dragon Book series.
There is only one mention relating to the Rottdragon, and no further information is given. It might be extrapolated from its name that it mimics the dog breed the Rottweiler in appearance or function. As such, the Rottdragon was possibly a type of hunting dragon.
|“||To tell the truth, he had felt sadder when he had to put down one of his favorite Rottdragons who had been injured in a fight.||”|
|— Grimbeard the Ghastly|