HI all I have been breeding my swordtails for a couple of generaltions now but wanted to try breeding my black female with a black male. however I found it hard to find one that doesn't have a black sword. I have heard that the gene that causes black fins is also cancerous for them, and I was wondering if anyone knew if that also includes his sword. He's such a handsome looking fish like a blue and black tuxedo... and now hes been swimming funny. sort of bobbing around and letting himself fall to the bottom before moving a fin. I isolated him because he lived with a puffer and didn't want him to become food.... but is there anything i can do to make him comfortable or if it is cancer whats the humane thing to do?