Irradiation of different fish was carried out either under Condition A or Condition B. Under Condition A, the distal part of the cone was located 2 mm from the fin (in water) so as to mimic an effect on tissues located 2 mm deep from the skin surface, i.e. the water separating the distal end of the cone from the skin of the fish was used to mimic deep tissue and the chances viewed on the fish skin