Polychaete Perinereis aibuhitensis is in great demand as fishing bait in Japan. However, P. aibuhitensis for fishing bait is imported from Korea and China. In preparation for coming restrictions such as resource depletion, it is indispensable to cultivate P. aibuhitensis domestically. Understanding the life history of P. aibuhitensis is necessary for domestic aquaculture. In the present study, we analyzed serotonin, which is involved in diurnal rhythm regulation in vertebrates, as well as tryptophan metabolites (kynurenine and indole-3-acetic acid). Mass spectrometric analyses were used in this study to detect serotonin, kynurenine, and indole-3-acetic acid in the head of the P. aibuhitensis. Serotonin production, as well as kynurenine production, was found to have no significant diurnal variation in P. aibuhitensis. Notably, there was a diurnal rhythm in indole-3-acetic acid synthesis in P. aibuhitensis. These results indicate that indole-3-acetic acid, rather than serotonin, plays an important function in the diurnal rhythm of P. aibuhitensis. These findings suggest that P. aibuhitensis could be efficiently reared and produced in Japan, if we can artificially support its optimal living environment that can maintain the diurnal rhythm of indole-3-acetic acid even in high-density farming.

In this study, a laboratory-selected high-temperature resistant strain of Undaria pinnatifida obtained from crossbreeding was evaluated for growth and productivity under three outplanting periods of varying water temperature levels: high (September 29, 2021; 25.4°C), middle (October 15, 2021; 24.4°C) and low (October 31, 2021; 22.2°C), in a cultivation site in the Shimane Peninsula. Our results showed that seedlings were lost significantly for the conventionally used strain (the control strain NT₂♂NT₂♀; CS) outplanted during the high-temperature period. On the other hand, the high-temperature resistant strain (IS₁♂NT₂♀; RS) grew well, suggesting the possibility of early shipment. Cultivation of this strain yielded shipping size U. pinnatifida with an average weight of over 100 g per individual upon harvest in early January, a period when the trading price of fresh U. pinnatifida is high. Furthermore, the January to March harvests showed that the RS outplanted during the high and middle-temperature periods produced harvest amounts that were 1.8 to 3.3 times higher than that of the CS outplanted during the low-temperature period. The use of the RS in U. pinnatifida cultivation sites is therefore expected to make a stable and improved production.

Although Sinonovacula constricta used to be a major clam that was caught in the muddy tidal flats in Ariake Bay until the 1980s, the harvest drastically decreased in the 1990s. Saga Prefecture took measures to recover the fishery resources by releasing clams to enhance the cycle of reproduction between 1997 and 2018, and the released young clams showed remarkable, stead growth with high biological productivity. In this study, we investigated the survival rates and the growth of juvenile clam after released in four tidal flats. Moreover, we explored the relationship between the tide height and the secondary production based on those results. According to the results of this study, the biomass could reach up to 4,698 g Wet Weight (gWW)/m². In addition, the amount of the secondary production ranged from 1,456 to 4,127 gWW/m²/yr, which is more than the secondary production of clams (Ruditapes philippinarum) in Ariake Bay. Furthermore, this data showed a negative correlation between the tide height and the secondary production. Considering the above results, the further discussion and research on this issue with the utmost effort are needed.

We examined the influence of total suspended solids (TSS) on the color and microstructure of shell nacre in freshwater mussel Sinanodonta woodiana for efficient half-pearl production. In conditions with a high TSS concentration (>10 mg/l) correlated with abundant freckles in the nacre (R = 0.51; p < 0.001), which appeared nearly round and were 0.5 ± 0.2 mm in size. Mussels from a high TSS concentration showed a thin whole nacre layer (250.9 ± 4.3 µm), thin nacre tablet thickness (0.43 ± 0.01 µm), lowest yellowness index (7.8 ± 0.7), and brightness (56.6 ± 0.4). In contrast, conditions with a low TSS concentration (<10 mg/l), the inner shell produced few freckles, a thick whole nacre layer (554.1 ± 3.8 µm), thick tablet nacre thickness (0.50 ± 0.01 µm), and strong gold color. Based on the present results, a TSS concentration of <10 mg/l is recommended for freshwater half-pearl aquaculture in Indonesia.

The Japanese eel (Anguilla japonica), is listed as “Endangered” by the IUCN. Understanding eel riverine habitat is useful in considering conservation strategies. This study sought to determine the relationship between environmental DNA (eDNA) concentrations derived from Japanese eels, water quality, and river structure in three small rivers in Nagasaki, Japan. eDNA was detected at 14 of 15 sites (93%). The concentration of eDNA in brackish water was significantly higher than that in freshwater and was correlated with water depth. Eel occurrence throughout the river suggests that Japanese eels are adapted to diverse riverine environments.

To improve breeding techniques for aquarium fishes, artificial reproduction was induced in green pufferfish (Dichotomyctere fluviatilis) specimens from India, following hormone injection in full-strength sea water, and subsequent spawning behavior, morphological development, and growth observed. Parental fish scattered more than 70,000 demersal adhesive eggs per one female (0.73 ± 0.05 mm in diameter) on the tank floor, without any subsequent egg protection. Hatching occurred 4 or 5 days after spawning. The larvae (1.87 ± 0.19 mm in notochord length) were reared comparatively easily, being initially fed Branchionus plicatilis sp. complex, and grew to 88.75 mm mean standard length after 360 days. The results of the present study should provide useful information for future breeding trials of Dichotomyctere species.