The force has used Tasers since 2005
Police fired a Taser "stun-gun" at a dog after it bit an officer trying to break up a fight in Plymouth.
About 18 officers were called to Bonville Road on Wednesday evening after reports of men fighting with baseball bats.
A Staffordshire bull terrier bit one officer on the leg and a Taser was used on the "violent animal", said police.
The officer was treated in hospital and the dog which did not require treatment was handed back to its owner.
A spokeswoman for Devon and Cornwall Police said it was legal to use a Taser against an animal.
It was the first incident of its type for the force which introduced Tasers in 2005.
Three men, aged 38, 36 and 18, all of Bampfylde Way, were arrested on suspicion of assaulting, one of them in connection with injuries to a police officer.