What is the importance of the "rumble fish," and why does the Motorcycle Boy let all the animals free at the end of Rumble Fish?
Is this because inside he feels as if he himself is constantly fighting, and because he is "crazy"?
I assume that the Motorcycle Boy sees a symbolic connection with the "rumble fish" in the pet store. The rumble fish are actually Siamese fighting fish--beautifully colored fish that must be separated from others of their species; if put in the same tank, the fish will fight--rumble--until they kill each other. The Motorcycle Boy sees similarities between the fish and the different gang members--including his brother, Rusty-James--who, without his interference, would kill each other in gang fights. The fiercely independent Motorcycle Boy wants to release the fish, along with the other animals, so that they can have their freedom, much in the same way that he lives his own life and encourages an end to the gang violence.