In the previous papers1)2), it was shown that a considerable effectiveness in keeping quality of sardine and mackerel was obtained on treating with chlorotetracycline under appropriate conditions. The present report deals with various possible procedures for the treatment of Pacific round herring with chlorotetracycline on a practical scale, aboard ship immediately after catching and/or on shore after landing. The results indicate that the spoilage of fish was retarded markedly by storage aboard ship in sea water containing 10 p.p.m. of chlorotetracycline and ice containing 5 p.p.m. of chlorotetracycline or by storage in ice containing 5 p.p.m. of chlorotetracycline after landing without treatment with chlorotetracycline sea water on the boat. The effectiveness of chlorotetracycline in extending the storage life was tested under two storage conditions: 15 to 20°C. and -1 to 2°C. By judging from organoleptic examinations and values for total volatile bases and histamine, It was found that maximum prolongation of storage life over that of the control was 90% at 15-20°C. and 40% at -1 to 2°C.