The present study was undetaken to investigate the changes in the bacterial counts and flora of horse mackerels, Trachurus japonicus, during the storage by partial freezing.
The fish samples were stored at -4°C (partial freezing), and a part of these were removed from the storage after the periods as described later and examined organoleptically, chemically, and bacteriologically. Enumeration and isolation of bacteria were conducted with a smeare plate method using 50 percent seawater agar medium. Identification was based chiefly on the schemes of S_HEWAN et al., and O_KUZUMI et al.
The bacterial count of the sample examined immediately before storing, was 1.8×10⁵per cm² of skin, and the majority of the isolates from the skin consisted of the groups of Pseudomonas III/IV-NH, III/IV-H and Vibrio. However, after 12 days of storage the count decreased to 6.7×10⁴, and the combined percentages of the above three groups decreased strikingly, while those of Moraxella, Acinetobacter and Flavobacterium-Cytophaga groups increased. After 40 days the bacterial population amounted to 10⁵, and the members of Pseudomonas I/II and an undetermined group appeared newly, while those of the above three dominant groups, Moraxella etc., disappeared markedly. After 3 to 4 monthes the bacterial numbers reached maximum values of 10³ and the samples gave out a typical offensive spoilage odor, and almost the entire population towards the end of the experiment consisted of the group of Pseudomonas I/II.