Information on population genetic structure, movement, and distribution is fundamental for effective management of marine species. In the western North Pacific, the common minke whale faces both bycatch and commercial whaling, the latter having resumed in Japanese waters in 2019. In this study, we refined the population genetic structure and spring–summer spatial distribution of this species using 6196 genetic samples collected in feeding grounds and migratory corridors during 1994–2024. Genetic analyses of the mitochondrial DNA control region and 16 microsatellite loci confirmed the previously recognized Sea of Japan–Yellow Sea–East China Sea (J) and Sea of Okhotsk–West Pacific (O) stocks, which overlapped along the Pacific and Sea of Okhotsk coasts of Japan. Spatial analyses identified fine-scale differences in distribution by stock, sex, and sexual maturity class. In both stocks, mature whales were found farther offshore than immature whales. In the J stock, both sexes were concentrated in coastal waters, whereas the O stock exhibited a broader distribution that varied by sex and maturity class, with mature males being found more frequently offshore. These findings have important implications for stock assessment and management and may inform future management strategies for western North Pacific common minke whales.
Excessive feeding is often used in aquaculture to grow farmed fish larger and more quickly. Meanwhile, recent studies using teleosts reported negative effects of a high-fat diet during the postpubertal period on fertilization, embryonic development, and hatching in the next generation. The current study aimed to clarify the effects of frequent feeding, resulting in an increased total amount of feed provided, only during the post-hatching prepubertal period on the timing of puberty and postpubertal reproductive ability. The medaka were divided into two groups: one with three feedings and the other with six feedings per day during the post-hatching prepubertal period. Frequent feeding resulted in a mild advance in puberty and was associated with greater growth, with higher gene expression of gonadotropins in female pituitaries. The current study also indicates that frequent feeding during the post-hatching prepubertal period promotes earlier maturation and increases the number of eggs laid shortly after the first spawning, with no effect on fertilization or hatching rates. Taken together, increased feeding during the post-hatching prepubertal period enhances breeding efficiency, which may be due to increased gonadotropins mRNA expressions in medaka, and may aid the maintenance of captive strains.
The male red snow crab Chionoecetes japonicus is a key deep-sea fishery resource in the Sea of Japan; however, the fate of released soft-shell adult males remains poorly understood. We investigated the major factors affecting subsequent recapture of soft-shell adult males under commercial fishing conditions. From 2016 to 2025, 802 soft-shell adult males were tagged and released off Fukui Prefecture, Japan, yielding 920 release events, including re-releases. Recapture status by the end of the study period was analyzed using a generalized linear model with sea surface temperature (SST), cold-water treatment (CT; immersion in 2 °C seawater for approximately 5 s to expel trapped air), carapace width, and follow-up period as explanatory variables. Recapture probability increased significantly at lower SSTs, with CT, and with longer follow-up periods, whereas carapace width had no significant effect. After averaging predicted probabilities over the observed follow-up periods, the predicted recapture rate of CT-treated crabs reached 42.8
Argulus coregoni is an ectoparasitic crustacean that infests salmonid fishes and causes economic losses in rainbow trout Oncorhynchus mykiss aquaculture. However, effective control methods have yet to be established. This study aimed to screen novel antiparasitic agents against A. coregoni by evaluating the antiparasitic efficacy of nine candidate compounds and their effects on parasite motility. First-stage larvae of A. coregoni were exposed to each compound for 1 h at two concentrations: a high concentration (agricultural/veterinary levels) and a low concentration (environmentally acceptable discharge levels). Post-exposure survival and swimming speed were monitored for 96 h, the latter quantified via DeepLabCut, a deep-learning-based individual tracking software program. All tested compounds other than trichlorfon and cyantraniliprole significantly reduced parasite survival at the high concentration. Notably, carbaryl exhibited parasiticidal activity even at the low concentration. In addition, seven compounds other than trichlorfon and ivermectin significantly suppressed swimming speed. These results suggest that motility impairment serves as a more sensitive indicator of efficacy than mortality alone, likely predicting parasite detachment in practical farm settings. This study identifies multiple potent candidates for A. coregoni control and establishes an artificial intelligence (AI)-based behavioral assay as a high-throughput, objective tool for future antiparasitic discovery in aquaculture.
The abundance of kuruma prawn Penaeus japonicus in Japanese waters has declined markedly since the mid-1990s. Despite this long-term decline, the underlying mechanisms remain poorly understood, limiting the development of effective stock management strategies. One consequence of reduced population density may be lower encounter rates between mates, potentially suppressing the species’ reproductive rate through a mate-finding Allee effect, in which the probability of mating decreases as population density declines. Yet, this mechanism has received little attention in conventional fisheries management. In this study, we investigated whether a mate-finding Allee effect occurs in P. japonicus populations in the Seto Inland Sea, using market-based sampling. Our results revealed a high proportion of unmated females (> 30
