It's a rule of thumb: if you notice something on a fish, look for the same on the other side
if the other side is the same - so the something is there, on the same place, similarly shaped - the something will most likely be natural, being part of how the fish is supposed to look
If it is not, it might be an individual variation, or a desease
This is especially handy looking at puts, which might be the result of flagellate desease, on the head of a fish arount the nose-holes and so on
yeap definitely missing a fin! but don't worry too much about it, as your cute lil bugger looks very healthy everywhere else, and considering it's gotten to this size, it means it has no trouble obtaining food!
I speak 12 languages fluently. English is my bestest. - Bush
I have no idea if he has alway's been like this,but there are no other fish in the tank that could bother him so i think he must have and he dose very well for himself