Age determination of chum salmon using scales becomes difficult as sexual maturation progresses. We examined and compared the working efficiency and accuracy of aging methods using scales, otolith surface, and otolith section with chum salmon. The percentage of age estimated correctly, cross-checked with known age by the otolith thermal mark and release protocol, was under 80% for the otolith surface and the common otolith sectioning methods in which otoliths are sliced to around 150 μm thickness. The accuracies were 100% using scales and thinner otolith sections of around 80 μm thickness. We therefore recommend employing the more accurate aging methods using scales and thinner otolith sections in line with the working efficiency and maturational conditions.

　Seedling production of the freshwater clam Corbicula sandai is usually conducted by inducing spawning of wild clams. However, because the condition index (CI) of wild individuals varies from year to year in Lake Biwa, the number of larvae obtained by this method is variable. In the present study, a novel culture method to increase clam CI was examined. Both the CI and growth of the clams suspended in Nishinoko Lagoon during winter were compared with those of clams cultured in a tank supplied with lake water and in the harbor adjacent to the Shiga Prefectural Fisheries Experiment Station on the east shore of Lake Biwa. The CI of clams cultured in Nishinoko Lagoon was significantly larger than that of wild clams and those cultured in the tank or the harbor. The suspended culture of clams in Nishinoko Lagoon during winter (from November to March), resulting in increased CI and shell length, possibly because the high productivity of the lagoon is expected to increase the number of larvae in artificial seed production.

　A histamine-producing bacterium was isolated from dried whole red-eye round herring Etrumeus teres in which histamine accumulation had been observed. The closest phylogenetic neighbor of this bacterial strain was Photobacterium angustum, which shares a 99.15% similarity based on 16S rRNA gene sequencing. An essential oil prepared from pomelo Citrus grandis rind showed strong inhibition of growth of P. angustum isolated from dried whole red-eye round herring. Histamine accumulation was also strongly depressed in dried whole red-eye round herring by the addition of the essential oil to the brine used in the salting process. Application of this citrus essential oil therefore effectively suppresses histamine formation in whole dried red-eye round herring.

　Red tilefish Branchiostegus japonicus meat exhibits poor thermal gelation properties, making it hard to utilize the fish as a raw material of gel products. We therefore investigated the effect of washing on the thermal gel-forming ability of red tilefish meat. Alkaline-saline (0.2% NaHCO₃+0.15% NaCl) washing was the most effective to improve the thermal gel-forming ability of the fish meat compared to other washings with fresh water, alkaline (0.2% NaHCO₃) solution, and saline (0.15% NaCl) solution. Myosin heavy chain (MHC) degradation in the fish meat was inhibited by alkaline-saline washing, as well as alkaline washing and saline washing. On the other hand, surface hydrophobicity of the proteins in red tilefish meat was significantly increased by alkaline-saline washing (p<0.05). These results suggest that the thermal gel-forming ability of red tilefish meat using alkaline-saline washing was improved by the increase of surface hydrophobicity of the fish proteins as well as by suppression of MHC degradation.

　Subzero temperature treatment before thawing is a method expected to prevent the drop of pH in thawed fish meat as well as to maintain its quality. In this study, the changes in pH, NAD, ATP and lactic acid in frozen chub mackerel Scomber japonicus meat by subzero temperature treatment before thawing were investigated. The method did not effectively prevent the pH drop in thawed meat and promoted color deterioration of dark meat in the case of chub mackerel, whereas it effectively prevented the pH drop in thawed bigeye tuna meat. Moreover, it was revealed that the rate of decrease in NAD level in chub mackerel was lower than that in bigeye tuna during the subzero temperature treatment at −10℃ before thawing. These results suggested that the drop in pH in thawed meat will be prevented by this method only in frozen fish meat having a rapid rate of NAD decrease during subzero temperature treatment before thawing.

　This paper analyzes the fresh bluefin tuna and frozen bigeye tuna markets in Japan using both empirical and field studies. First, the asymmetric price transmission in these two markets was estimated. Then, we conducted a field study to clarify the characteristics and transaction forms in these markets, and also reviewed previous studies in the literature. The empirical study showed the existence of positive and negative asymmetric price transmissions in both the fresh bluefin tuna and frozen bigeye tuna markets, respectively. The field study suggested that the difference in these asymmetric price transmissions, between even two similar goods, may be due to the conditions of transaction patterns and substitutional goods.