Thanks guys
I knew it was a stupid question but was puzzled as to how i'd never noticed it before.
it is quite a small sword to the tail so I think it could be as you say just a young fish thats just grown it.
Jim
This probably sounds strange and bizarre but I have all female swordtails
in my tank and just noticed that I have a male.
Is it possible for a female swordtail to change into a male?
Thanks