Usually when fish breed, you will end up with some type of deformity every now and again because of so much inbreeding in the industry. I recently had 300+ cory cat fry with 25 deformities. Most were midgets, never grew past 1/4 inch and eventually most died, I had a few survive that are now 6 months old.
Another batch I had, all mutant cory cats survived and they are 6+ years old now. Some were born with 1/2 a body and some had messed up fins.
I also have a guppy with a curved spine....she is 2 years old.
But most will survive common mutations like curved spines or deformed fins.