I think I have mosquito larvae in my fish tank.?

I dont no how they got in because I havent fed live food, apart from taking them out by catching them has anyone got ideas of removing them.or how long they'll live, I dont think they will do damage to my fish, Ive been told the fish could eat them, I thought I got them all the other day but I found another one this morning. I dont see them on the surface of the water. Could they be in the gravel? They are about an inch long and wriggle around the tank, I tested my water and its the best its ever been no nitrite/ammonia ph8. Any suggestion please