The population structure of yellow drum Nibea albiflora around Japan was examined based on nucleotide sequences of the mitochondrial (mt) control region. The mtDNA diversity values observed were lower in the Seto Inland Sea (SIS) and Ariake Sound (ARS) in Japan than those in the Yellow Sea (Qingdao) and East China Sea (Zhoushan and Xiamen). Phylogenetic analyses did not reveal any phylogeographic structures. However, the SIS and ARS populations in Japan were suggested to be significantly differentiated from the Yellow Sea and East China Sea populations by pairwise ΦST values. Significant genetic differentiation was also observed between the SIS and ARS populations, with the highest ΦST value among the five localities. The Bayesian Skyline plots (BSPs) for the SIS and ARS populations showed the female effective population size (fNe) did not increase until recently , while the BSP for the Yellow Sea–East China Sea population showed fNe notably increased. Although hierarchical analyses of molecular variance detected no significant grouping of localities, the SIS and ARS populations were well differentiated. Consequently, they should be treated as independent management units for future conservation and management.
This study evaluated immunity enhancement, resistance to Aeromonas veronii infection, and growth promotion of emodin administered orally at doses of 0, 20, 60, 80, and 140 mg kg⁻¹ in Micropterus salmoides (largemouth bass) for 28 days. The fish taking emodin at 80 mg kg−1 exhibited optimal growth performance, with 1.18
The cooked leg meat of red king crab (RKC, Paralithodes camtschaticus) is highly valued worldwide for its sensory appeal. Prior to commercialisation, RKCs are often held alive in onshore facilities for short periods, a practice known as “live holding”. This study comparatively evaluated the sensory characteristics of cooked leg meat obtained from commercial-size freshly caught wild RKCs (n = 8) and RKCs of similar size but subjected to 3-month live holding (n = 8), during which they were fed raw herring and shrimp. Quantitative descriptive analysis revealed that the odour attribute process was more intense (p = 0.004) in wild samples, whereas the live holding samples were perceived as more bitter (p = 0.039) and with a more intense juiciness (p = 0.019). However, differences in mean attribute intensity were small and unlikely to be identified by an ordinary seafood consumer. Instrumental colour measurement lightness (L*) was higher (p = 0.021) in live holding samples, whereas instrumental texture parameters did not differ significantly (p ≥ 0.05) between the groups. In summary, this study demonstrates that, for RKC, a 3-month live holding period with raw herring and shrimp as feed impacts only marginally the organoleptic properties of its cooked leg meat.
Despite the widely recognized impact of fish herbivory on macroalgae, few studies have quantified the specific contributions of individual species in Japan. We used visual censuses along belt transects to investigate the abundance of herbivorous fishes, and measured fish feeding intensity on deployed native brown seaweed Sargassum piluliferum from underwater videos, at two coastal sites off Nagasaki Prefecture, southwestern Japan, in 2016 and 2018. A total of eight herbivorous species were observed, with Girella spp. and/or Prionurus scalprum comprising the majority of roving herbivorous fish at both sites. However, herbivory was driven by only three species: Calotomus japonicus, Kyphosus bigibbus, and Siganus fuscescens. At Nomo, C. japonicus was the principal species responsible for removal of S. piluliferum. At Mie, S. fuscescens was the most dominant in herbivory in 2016, but its contribution declined markedly in 2018, leading to C. japonicus becoming the principal species responsible for the removal. These findings indicate that only a subset of herbivorous fishes, even at low abundances, significantly reduces Sargassum biomass, and that the key herbivores may vary between reef sites. Identifying these key species using algal assays is an important step toward targeted management of herbivorous fish to support seaweed bed conservation and restoration.
Water temperature strongly influences fish physiology, and body temperature in fishes often changes asymmetrically during cooling and warming. In pelagic fishes, body temperature commonly increases more rapidly during warming than it decreases during cooling, suggesting physiological regulation of heat transfer. However, the contribution of cardiac activity to this asymmetry remains unclear. Ambient water temperature was experimentally manipulated in captive amberjacks (Seriola spp.) and heart rate and abdominal cavity temperature were measured to examine the role of cardiac activity in heat transfer. Heart rate exhibited clear temperature hysteresis, forming a circular relationship with body temperature: heart rate was lower during cooling and higher during warming at the same body temperature. The heat transfer coefficient was consistently higher during warming than during cooling and increased with increasing heart rate. Complementary experiments using a dead fish were conducted to separate physical and physiological components of heat transfer. The heat transfer coefficient of the dead fish was lower than that of live fish, representing the physical component. After subtracting this component, the remaining physiological component also differed between cooling and warming phases. These results demonstrate that heart rate exhibits temperature hysteresis in fishes and contributes to asymmetric heat transfer during cooling and warming.
Recreational fishing is a major user of fishery resources alongside commercial fisheries. However, its operational characteristics remain poorly understood, and quantitative analyses have been limited. In Japan, recent amendments to fisheries legislation have promoted science-based resource management, highlighting the urgent need to improve data availability for recreational fisheries, particularly for catch and effort. In this study, we analyzed commercial passenger fishing vessel fisheries (CPFVFs) targeting Trichiurus japonicus in Tokyo Bay, where catches by commercial and recreational sectors have increased. To identify covariates relevant to catch per unit effort (CPUE) standardization, we analyzed SNS catch reports and constructed models to explain per-angler catch variation. The selected model retained environmental and operational covariates. Some covariates, such as month and water temperature, may contain abundance-related signals; whereas others, such as day of the week, seating position, angler density, fishing gear, and vessel-related effects, probably represent non-abundance-related variation to be controlled for in standardization. Mean tidal range, moon phase, and rain were interpreted as ambiguous covariates that may reflect both abundance-related and non-abundance-related processes. These results indicate that recreational catch rates should be interpreted within a CPUE standardization framework and provide a basis for incorporating CPFVFs into science-based stock assessment and management in data-limited coastal systems.
Infectious diseases pose a significant threat to kuruma shrimp (Penaeus japonicus) aquaculture, and oral transmission is considered one of the major infection routes. The stomach, where ingested feed is temporarily retained, is a key site for host-microbe interactions that may influence pathogen establishment. However, the ecological characteristics of stomach microbiota under actual aquaculture conditions remain poorly understood. In this study, we characterized the stomach microbiota of apparently healthy kuruma shrimp reared in four commercial aquaculture farms in Okinawa, Japan, using 16S rRNA gene amplicon sequencing with monthly sampling over 1 year. Bacterial community composition exhibited significant but modest temporal structuring across farms, with samples collected at the same time points showing similar community compositions regardless of farm origin, suggesting that shared environmental factors contribute to seasonal dynamics. The genus Photobacterium persistently dominated the stomach microbiota, and stomach communities were clearly distinct from those of the surrounding pond water. Despite this temporal signal, substantial inter-individual variability was observed. At the genus level, four taxa were consistently detected across samples (Photobacterium, Vibrio, Candidatus Bacilloplasma, and Pseudoalteromonas), though sequence-level diversity across farms limited the number of shared amplicon sequence variants. Species richness fluctuated across sampling periods without consistent changes in community evenness. These findings indicate that the stomach microbiota of kuruma shrimp is shaped by the interplay of shared temporal drivers and strong individual variability, providing an ecological baseline for future studies on pathogen establishment via oral transmission in aquaculture systems.
Shrimps regulate osmotic pressure by altering the amounts of free amino acids in their bodies. While changes in alanine (Ala) content are particularly significant, the molecular mechanisms involved in controlling Ala levels remain largely unknown. In the present study, we investigated alanine-glyoxylate aminotransferase 1 (AGT1), an l-Ala-degrading enzyme, using the kuruma shrimp Penaeus japonicus as a model to elucidate the regulatory mechanism of l-Ala levels in shrimps. We found that kuruma shrimp AGT1 is specialized for l-Ala degradation and does not catalyze the reverse reaction. Its optimum pH and temperature were approximately 8.0–9.0 and 50 ºC, respectively, which are similar to those reported for AGT1s from other species. Structural analyses revealed that the amino acid residues constituting the active site were conserved, and the predicted three-dimensional structure was similar to that of known AGT1s. Investigation of AGT1 gene expression in kuruma shrimp acclimated to different salinities showed that its expression level in the abdominal muscle was low and did not fluctuate significantly. This result suggests that AGT1 plays a minor role in the regulation of l-Ala content in the abdominal muscle of kuruma shrimp, implying the existence of other primary regulatory mechanisms in this tissue.
Understanding how the endemic and threatened Naru eagle ray Aetobatus narutobiei responds to fishing mortality is fundamental for evaluating its population dynamics and developing sustainable management strategies. This species has been both targeted in a long-term predator control program and subjected to over two decades of intense fishing pressure in Ariake Bay. Using an age-structured demographic model, we evaluated current fishing pressure and conducted different fishing scenarios to assess population responses. Catch-at-age data indicated that recruitment to the fishery began at age 0, with juveniles of both sexes comprising the majority of the catch. The finite rate of population growth (λ) of 1.119 year−1 was estimated under unfished conditions based on the base model. However, after incorporating age-specific fishing mortality into the base model, λ markedly declined to 1.042 year−1 under the current condition, indicating that this species is highly sensitive to fishing pressure. Elasticity analysis further demonstrated that juvenile survival had the greatest relative influence on the population growth rate. Stochastic simulations incorporating life-history parameter uncertainty under scenarios of constant fishing mortality across age classes revealed that delaying the age at first capture to 6 years, thereby exceeding female age at maturity, could substantially reduce the risk of population decline under scenarios of increased fishing mortality.
Although the Japanese mitten crab Eriocheir japonica exhibits high potential for aquaculture, cannibalism under rearing conditions limits productivity. However, a quantitative evaluation of the factors driving cannibalism remains lacking for the early juvenile stages, which constitute the most critical stage for aquaculture. Here, we aimed to quantitatively evaluate the combined effects of size ratio, mean size, food treatment (fed versus starved), molting, and elapsed days on the risk of cannibalism in early juveniles using a Bayesian multinomial mixed-effects model. The probability that the smaller individual was cannibalized significantly increased with a larger size ratio between individuals, starved treatment, and increasing elapsed days. Furthermore, the molting of the smaller individual in a crab pair significantly elevated its risk of being cannibalized. In contrast, cannibalism slightly decreased in pairs composed of larger individuals, and it was strongly suppressed when the larger individual had molted. It was extremely rare for the larger individual in a pair to be the victim. Our findings suggest that cannibalism in early juvenile Japanese mitten crabs is a context-dependent foraging strategy based on a cost–benefit trade-off. These quantitative insights provide a foundational basis for developing specific husbandry guidelines to mitigate cannibalism in Japanese mitten crabs in aquaculture.
The feeding ecology of the cutlassfish Trichiurus japonicus in Osaka Bay was investigated using stomach content analysis and stable isotope ratios from monthly samples collected between November 2018 and February 2022. The index of relative importance indicated that fish dominated the diet (95.97
To examine the ability of tactile discrimination, Japanese eels were trained to perform a tactile discrimination task using a pool equipped with four pipes. One of the pipes was fitted with silicone rings, which served as the tactile stimulus, and the other three pipes were unmodified. Only the pipe with the tactile stimulus was open and accessible, allowing the eels to enter the pipe as a reward. All five eels successfully learned to discriminate between the pipes and consistently selected the one with the tactile stimulus. The eels maintained this discrimination under dark conditions, demonstrating that visual cues were not required. In addition, local anesthesia applied to the olfactory organs did not impair performance, demonstrating that olfactory cues were not involved. Also, the eels continued to perform the task accurately following immersion in streptomycin, which impairs the function of hair cells in the lateral line system, implying that the lateral line organ did not contribute to the tactile discrimination. These findings highlight the reliance of Japanese eels on tactile information. The findings were compared to previously reported abilities in visual, spatial, and hydrodynamic discrimination.
The large-scale loach Paramisgurnus dabryanus, introduced from continental Asia, coexists with the native dojo loach Misgurnus anguillicaudatus in Japan, likely causing genetic contamination of native populations through hybridization. Previous mitochondrial DNA (mtDNA) analyses have identified two divergent lineages of large-scale loach (groups 1 and 2), whereas nuclear DNA analysis of the RAG1 region revealed no differences between these two groups. In this study, we developed a novel mtDNA polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) method targeting the cytochrome b region using AvrII and NcoI for rapid identification of groups 1 and 2 based on distinct fragment profiles. Consistent with previous research findings, nuclear DNA marker analyses revealed no differences between groups 1 and 2. This new marker enables efficient screening of large-scale loach lineages, facilitates distribution surveys, and clarifies the introduction pathways of this species.
In May–July 2023, diarrhetic shellfish toxin (DST) exceeding the regulatory limit was detected in shellfish from Kyoto for the first time, and the dominant toxin was dinophysistoxins-3 (DTX3). The toxic marine dinoflagellate Dinophysis, including D. acuminata, D. caudata and D. fortii, was observed. To identify the potential cause of the DST occurrence, unialgal cultures of the three species were isolated from Miyazu Bay to investigate their growth characteristics and toxin production. Additionally, 36 strains of D. fortii were incubated for a month for toxin analyses. In the growth experiment, D. acuminata showed the highest specific growth rate (µ) of 0.32 ± 0.033/day, followed by D. caudata (0.23 ± 0.067/day) and D. fortii (0.20 ± 0.024/day). Toxins produced were DTX1, okadaic acid (OA) and pectenotoxin-2 (PTX2) in D. acuminata and D. fortii, and only PTX2 in D. caudata. In the stationary phase, DTX1 yield was higher in D. fortii (485.3 ± 150.07 ng/mL) compared with D. acuminata (13.8 ± 2.15 ng/mL), as was the DTX1/OA ratio (D. fortii: 61–318, D. acuminata: 0.122–0.249). Furthermore, 97
Seaweed beds play a crucial role as primary production sites in coastal ecosystems but face threats by isoyake (the denudation of rocky shore seaweeds) and other environmental factors. To support effective conservation and enable early detection of seaweed bed decline, more efficient monitoring techniques are needed to address the limitations of conventional survey methods. In this study, we developed a technique to simultaneously detect four major seaweed and seagrass families (Laminariaceae, Sargassaceae, Zosteraceae, and Alariaceae) and bedrock (five categories in total) from underwater images using convolutional neural network-based transfer learning and fine-tuning. The developed method maintained high prediction accuracy across images taken under various environmental conditions, highlighting its potential for practical applications.
Triploid oysters have become an indispensable component of the oyster industry in China. Allotriploid oysters (Crassostrea gigas ♀ × C. angulata ♂) demonstrate faster growth rates and lower fecundity than their autotriploid counterparts. However, the molecular basis of their lower fecundity is still unknown. In this study, we employed comparative transcriptomics to investigate the molecular basis underlying the differences in gametogenesis between male autotriploid and allotriploid C. gigas. Transcriptomic analysis (allotriploid versus autotriploid) identified 1367 differentially expressed genes (DEGs), comprising 672 significantly upregulated and 695 significantly downregulated genes. Gene Ontology (GO) enrichment analysis revealed that these DEGs were predominantly enriched in biological processes such as translation, peptide biosynthetic processes, peptide metabolic processes, and cell–cell adhesion. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis indicated these DEGs were enriched in pathways including ubiquitin-mediated proteolysis, ribosomes, and retinol metabolism, etc. These findings suggest that the differences in protein translation, synthesis, and metabolism may be related to the differences in gametogenesis between autotriploid and allotriploid oysters. Specifically, both protein synthesis and degradation activities were found to be more pronounced in allotriploids compared with autotriploids. This study provides valuable insights into the molecular mechanism of gonadal development differences between autotriploid and allotriploid oysters.
This study examined the effectiveness of recombinant gonadotropins derived from Japanese eel Anguilla japonica for inducing oocyte maturation and ovulation in female whitespotted conger Conger myriaster. Recombinant follicle-stimulating hormone (rFSH, 500 µg/kg body weight, BW) was administered weekly to females at the pre-vitellogenic and early vitellogenic stages to promote vitellogenesis. At the migratory nucleus stage, as indicated by cytoplasmic clearing in the oocytes, recombinant luteinizing hormone (rLH, 500 µg/kg BW) was administered to induce final oocyte maturation and ovulation. In Experiment 1, seven of eight females (87.5
This study examines the role of crabs as potential predators of hatchery-reared spotted halibut Verasper variegatus juveniles in Matsukawa-ura Lagoon, a shallow brackish lagoon in Japan and a key release site for this species. Monthly trap surveys conducted from 2012 to 2014 at 12 locations within and around the lagoon captured 3768 individuals representing 36 species, including 10 potential predator species. The shore swimming crab Charybdis japonica and Japanese mitten crab Eriocheir japonica were the most abundant crab species, accounting for 54.9
Red sea bream Pagrus major is one of the most important aquaculture species in Japan. Stereo cameras are widely used for monitoring fish growth. However, growth monitoring using stereo cameras encounters measurement issues, such as depth-related bias, which may be influenced by the fish’s depth distribution. Swimming speed is a key indicator of fish welfare and affects depth distribution. The objective of this study is to elucidate the spatiotemporal characteristics of red sea bream in aquaculture environments, with a particular focus on fork length and swimming speed. Experiments were conducted at the same site across four different seasons. Fork length and swimming speed were measured using four stereo cameras placed at different depths. The depth distributions were assessed using a single-beam sonar during summer and autumn. The results revealed a significant depth-related bias in fork length measurements throughout the year. Swimming speed varied with depth, season, and fish size. These findings suggest that the depth at which stereo cameras are installed is a critical factor influencing the accuracy of fork length measurements. In conclusion, the optimal depth for fork length measurement of red sea bream aquaculture is the middle depth of fish school.
