The victim, aged 64, was spending his summer holidays in the Valencian town of Benicarló with his wife and three children.
According to online Spanish daily El Mercantil Valenciano, the two men argued in the landing of the apartment block they were both living in before the aggressor pulled out a shotgun and fired it at the dog owner’s face.
Local police, Civil Guard and paramedics were quickly called to the scene but nothing could be done to save the victim’s life.
The aggressor offered no resistance when he was arrested.
Neighbours told the local daily the pair had already argued before, the aggressor reprimanding his soon-to-be victim for not letting him have his afternoon nap.
The murder took place at 3.30 pm, prime siesta time in Spain.