Are my Oscar Fish fighting or playing when they ram into each others sides?

Juvenile Oscars often play rough with

each other by locking jaws and may even attack the sides of a fish,

usually inflicting little damage. As these fish mature, even while

they are as small as 4 or 5 inches in length, their territorial

instincts kick in and these once playful antics can cause real

damage. This destructive behavior typically occurs in small

aquariums. Oscars will grow to a length of almost 12 inches and

require an aquarium of at least 75 gallons for a single fish or 125

gallons for a pair.

When two oscars of the same sex are

kept together one will normally become dominant over the other.

Sometimes they will enforce their dominance by biting the sides of

the less dominant fish; at times they will go to the extreme of

knocking off scales which may allow infections to set in. Injured

fish should be removed and medicated. To help with territorial

aggression, tank decorations can be rearranged on a regular

basis.