thats fine, your not mean. it was sick. i think it had decapsulated worm eggs in its tail because of the snails in the tank, but im not sure. it was black around tailfin and other fins. i looked up what it had from the symptoms, and thats what it said. It also could of been from the two-day power outtage which i wasnt home for. Another thing is when I toog it out of the tank it had a little buldge at the end of its ribcage. is that bad or contagious because theres still a mosquito fish in there.