Live transportation is a critical component of fish farming and hatchery release. To optimize hatchery-release techniques and improve the survival rate of marbled rockfish (Sebastiscus marmoratus, Cuvier 1829) juveniles, the effects of varying transport durations (2, 4, 6, and 8 h) and densities (60, 90, 120, and 150 kg m⁻³) on the physiological indicators of the fish and water quality were investigated under controlled laboratory conditions. We found that as transport duration and density increased, water quality significantly deteriorated, with ammonia nitrogen levels rising and dissolved oxygen content and pH levels decreasing. Physiological indicators including levels of lactate, cortisol, and malondialdehyde and activities of superoxide dismutase, alkaline phosphatase, and glutamate oxaloacetate transaminase notably increased, indicating that the fish experienced heightened stress during transport. Additionally, the mortality rate of juveniles increased significantly with increasing density and transport duration. The high mortality rate might be associated with sustained elevated cortisol levels and liver damage. Our results are helpful for determining the optimal transport conditions for S. marmoratus juveniles and also provide valuable insights for improving transport techniques for other aquatic animal species.

Group discrimination is a critical prerequisite for studying fish population dynamics, implementing effective fisheries management, and evaluating the outcomes of stock enhancement programs. However, research on group differentiation of Oplegnathus fasciatus (Kroyer, 1845), an economically important species in the East China Sea, remains limited across different geographical regions. We conducted a comparative analysis of trace element concentrations, including iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), chromium (Cr), cadmium (Cd), and mercury (Hg), as well as metalloid arsenic (As), in the muscle tissues of three distinct groups of O. fasciatus: the farmed group, the Yangtze River Estuary group, and the Zhongjieshan group. Trace elements were detected using inductively coupled plasma mass spectrometry. Group classification methods such as cluster analysis, stepwise discriminant analysis, and random forest were used to differentiate the groups based on these eight trace elements. Consequently, significant differences were observed in the concentrations of Fe, Cu, Zn, Cr, As, and Hg among the groups (p< 0.05), while differences in Mn and Cr were not statistically significant (p > 0.05). Discriminant analysis showed that cluster analysis effectively differentiated the farmed group from the Zhongjieshan group. Stepwise discriminant analysis achieved an overall accuracy of 85.1%, while the random forest model demonstrated an accuracy of 92.86%. These findings suggest that trace element concentrations could be applied to effectively distinguish among groups of O. fasciatus, with the random forest model outperforming traditional statistical methods to some extent. Our results are relevant to the activities of stock release and fisheries management.

Fulgoraria rupestris is a predatory marine gastropod belonging to Neogastropoda and possessing considerable taxonomic significance. However, research on this species remains limited. We acquired the complete mitochondrial genome of F. rupestris through second-generation sequencing and conducted an analysis of its genome structural features. The mitochondrial genome of F. rupestris spans a total length of 16,223 bp and encompasses 37 genes (13 protein-coding genes (PCGs), 22 transfer RNAs, and 2 ribosomal RNAs). Notably, most tRNAs exhibit the typical cloverleaf structure, but there is an absence of the Dihydrouridine (DHU) arm in the trnS1 and trnS2 genes. The A + T content is 68.67%, indicating a pronounced AT bias. Additionally, we conducted a selection pressure analysis on the mitochondrial genomes of four species within Volutidae, revealing that all PCGs are subjected to purifying selection. In comparison to other species within Neogastropoda, F. rupestris shares an identical gene arrangement. Additionally, based on mitochondrial genome sequences of the 13 PCGs from 50 species within Neogastropoda, we constructed a phylogenetic tree. The phylogenetic tree indicates F. rupestris forms a clade with species within the family Volutidae (Cymbium olla, Neptuneopsis gilchristi, and Melo melo). This study serves as a valuable reference for future research on F. rupestris, offering insights for the upcoming phylogenetic and taxonomic classification within Neogastropoda. Furthermore, the findings provide valuable information for the development of genetic resources in this context.

Larimichthys polyactis, a key species in East Asian coastal ecosystems, shows distinct seasonal changes in density distribution, shaped by environmental factors and migratory behaviors of two dominant populations (East China Sea and South Yellow Sea). This study explored its 2023 density dynamics in Zhejiang coastal waters using quarterly surveys across 83 stations, combined with generalized additive models (GAM) and random forest (RF) models. Results showed that RF outperformed GAM overall, with bottom dissolved oxygen (SBO), salinity, and depth as the most influential environmental drivers. Density peaked in summer (77.88 thousand ind./km²) in central and northern offshore areas, dominated by the South Yellow Sea population migrating into the region. Autumn densities (3.76 thousand ind./km²) declined sharply as populations moved to overwintering grounds, while spring (0.41 thousand ind./km²) and winter (0.26 thousand ind./km²) densities were lowest. These findings highlight the role of seasonal environmental filters and population-specific migrations in shaping distribution patterns. RF models provide robust tools for predicting habitats, supporting seasonally tailored conservation strategies to protect critical spawning, foraging, and overwintering areas, which are vital for the sustainable management of this ecologically and economically important species.

Background: This study determined the complete mitochondrial genome sequence of the marine crab to elucidate its phylogenetic position within Heterotremata, specifically the superfamily Goneplacoidea, and to explore the biological significance of its genetic composition and arrangement. Methods: The complete mitochondrial genome of Eucrate alcocki was sequenced using the Illumina platform and de novo assembled. Genome annotation and structural analysis were performed using MITOS2 and PhyloSuite. Phylogenetic relationships were reconstructed based on 13 protein-coding genes from 59 heterotrematan species using both Bayesian inference and maximum likelihood methods. Results: The mitochondrial genome of E. alcocki is a circular molecule of 15,720 bp with 72.2% AT content and a unique F-H-ND5 → H-F-ND5 gene rearrangement. Phylogenetic analysis robustly places E. alcocki in a distinct clade with Entricoplax vestita (BI = 1.00, ML = 100%), separate from the congeneric species Eucrate crenata and E. solaris, suggesting potential paraphyly within the genus Eucrate. Conclusions: This discovery provides preliminary evidence suggesting existing crab classification systems and molecular evidence for further understanding the evolutionary history of crabs. Our findings demonstrate that genomic characteristics hold significant value in revealing evolutionary pathways and can serve as a foundation for more comprehensive taxonomic and evolutionary research in the future.