Skewed sex ratio has often been observed in hybrids, but the sex was always determined by gonadal phenotypes. Here, we artificially induced reciprocal hybrids between pink salmon and masu salmon and then examined the genetic sex ratio in the hybrids based on the presence or absence of the sex-determining gene sdY. As a result, the sex of 8-month-old hybrids between pink salmon female×masu salmon male and masu salmon female×pink salmon male skewed to female, while 12-month-old hybrids between masu salmon female×pink salmon male were exclusively male. Since the sex ratio between the early embryos and hatching alevin was 1:1, it was considered that the skewed sex ratio was due to the difference of survival rate between genetic males and females.
Recreational angling is a dominant use of inland fish resources. Since recreational angling is a leisure-based activity, the stock manager must meet two objectives: 1) maintain fish stocks, and 2) maximize angler satisfaction with limited catch. To achieve these goals, it is important to evaluate the relationship between angler satisfaction and catch in order to construct a management strategy, because catch is one of the most important connections between fish stock and angler satisfaction. In this study, the relationships of four angling target species which have different biological and social traits were investigated. The results of a questionnaire survey of 639 anglers in total revealed four types of orientation: 1) the catch of endemic target fish strongly enhances angler satisfaction, 2) the existence of endemic fish increases angler satisfaction for all anglers, 3) fish size has a greater influence than number of fish for anglers who target fish that grow larger (i.e. trophy anglers), and 4) anglers desire more fish when the target fish has higher value as a food (i.e. consumption orientation). For the sustainable use of fish stocks for recreational angling, not only the biological traits of stocks but also anglers' orientation toward catch should be considered.
Interference color and luster are representative characteristics that determine the beauty and economic value of cultured Akoya pearls. To understand the mechanism of appearance, we investigated the influence of thickness of the whole nacreous layer (range: 0.28-1.57 mm) and crystal microstructure, i.e. the thickness of one CaCO3 crystal tablet (0.32-0.42 µm) and the coefficient of variation of crystal thickness on the intensities of interference color and luster of pearls. A significant positive correlation between interference color and both whole thickness of nacre (r=0.669−0.863) and crystal tablets (r=0.613) was detected. A negative correlation between interference color and coefficient of variation of crystal thickness (r=−0.651) was also observed. On the other hand, no significant correlation was observed between luster and these crystal structure factors. Results of multiple regression analysis suggest that the degree of influence on the interference color is large in order of thickness of nacre, thickness of one crystal tablet, and coefficient of variation of crystal thickness. Our results will contribute to the development of a technique for producing high-quality Akoya pearls by enhancing their interference color.
A lateral flow immunoassay kit was experimentally introduced to monitor paralytic shellfish toxins (PSTs) in two species of bivalves, ark shell and Japanese cockle, in Osaka Bay. The regression equation between the Test-line/Control-line ratio and the toxicities in mouse bioassay was used to estimate the toxicities of other samples. Specimens of ark shell and Japanese cockle were collected in the eastern part of Osaka Bay after the density of toxic dinoflagellate Alexandrium catenella fell below the warning level set in Osaka prefecture in 2019. The toxicity of Japanese cockles was estimated to be below the regulatory level of 4 MU g−1 by the lateral flow immunoassay kit on June 25 and the samples collected thereafter were tested by the official testing method, mouse bioassay (MBA) for PSTs. Japanese cockles were determined to be below the regulatory level for three consecutive weeks, which is the minimum period to resume harvesting of shellfish. Because the MBA was replaced by the PSTs testing kit, the number of MBA in 2019 was largely reduced in this experimental monitoring for Japanese cockle. The result indicates that this kit is useful for reducing the cost of PST monitoring.
We examined the contents of six imidazole compounds—balenine (Bal), carnosine (Car), anserine, histidine, 3-methylhistidine and 1-methylhistidine—in five parts of pike conger Muraenesox cinereus caught in Hyuga-nada. The results showed that the Bal and Car contents in the middle part of the trunk muscle were 329±69.6 µmol/100 g (n=6) and 979±227 µmol/100 g, respectively. Car content was higher on the trunk's head side, whereas Bal content was higher on the tail side. In the muscle refrigerated at 5℃, Car reduced to 2%, whereas Bal showed almost no change over time until day 3. These findings suggest that hydrolytic enzyme activity in pike conger muscle is high in Car and low in Bal.