A few weeks ago a breeder brought me a pair of kois in a bag. At the time I saw nothing wrong, but when I got them into the tank I thought the male was keeping his dorsal fin down because he was a little timid of his new surroundings. There were no other fish in the tank but him and his female partner, its a 2ft x 1ft by 15 high that I use for quarantine or sometimes breeding.

This male retains his dorsal fin in this position, which I would say is about 30 degrees to his body. I will try and get a photo soon. I cant tell if it is a deformity which should have been culled or if the fin would become more erect if he flexed it. Is this a genetic defect, or is it environmental due to inproper rearing conditions?