Gross pathological changes of white muscle. (A) A red focal change in the muscle of the craniodorsal region of the abdominal wall. (B) An incision through a red focal change showing discolouration extending deep into the fillet. (C) A melanised focal change detected in the same anatomical location in a different fish. (D) A melanised focal change with extensive amounts of a whitish tissue extending into the depth of the fillet. (E) A muscle fillet with two faint melanised lesions (arrows) and one red focal change (arrowheads).