Did you mean...
"My fish are sick. Their tails and fins are no longer in a striaght line, they are wavy, like they grew that way. I thought fin rot but they look like they are growing, not rotting." ?
If so, could be poor nutrition. Did this just start? How old is the food you're feeding? It isn't fuzzy looking? What kind of fish, are they adults/juvies, how long have you had them. What do you feed them.
If I mis-interpreted your question feel free to clue me in.