When Fish Fight

Be careful about what mix of fish you place in your tank. Placing incompatible fish in the same aquarium can lead to life-threatening bacterial, fungal and parasitic disease or injury and even death from attack.

Many fish hobbyists — especially beginners — want variety in their new aquarium. All too frequently, fish that are attractive but maintained separately in the pet store won’t get along in the same aquarium or outdoor pond. Intimidated fish, which manage to survive attacks by a dominant individual, may go without food if they spend too much time hiding under a rock or in the corner of the aquarium.

The solution usually requires physically separating the aggressive and submissive fishes. For example, larger koi commonly will injure or even kill small goldfish. Members of the same species may even kill and eat smaller or weaker members of the same species.

A responsible pet staff will usually advise you on which fish will get along. Despite this advice, some aquarists still gamble and place incompatible fish in the same aquarium. As a general rule, larger fish tend to beat up smaller fish. And cichlids tend to be aggressive. And it isn’t just same-sex fish that fight. Male-female blow-ups are also common.

Dealing With Trouble in the Tank

• Consult with your pet staff or knowledgeable members of your local aquarium society.
  
• Do your homework. There are plenty of books and magazine articles that discuss the behavior and habits of most pet fish species.
  
• Provide plenty of structure in your aquarium in the form of rocks, corals, plants and driftwood. These items can provide life-saving refuge for your smaller and more submissive pet fishes.
  
• Keep your fish well-fed but not overfed. A feeding that lasts no more than three minutes, usually only once a day, is enough for most adults.