If you have an aggressive cat or an aggressive dog a trip to the veterinarian is a good idea to rule our injuries or a medical issue with your pet.
Aggressive Pets
Oddly enough some of the most aggressive dogs are the small dog breeds such as the Chihuahuas or the Miniature Pinschers.
Aggressive Pets
Many species of aquarium fish are naturally aggresive by nature and can only be kept with like species. Aggressive fish will almost always eat fish smaller than them.