Steroid hormones, recognized as emerging environmental contaminants, have garnered increasing attention in recent years. The present work studied the distribution characteristics in the environment, bioaccumulation in aquatic products, and the associated environmental and health risks of typical steroid hormones from commercial freshwater aquaculture farms operating under different aquaculture modes (monoculture and polyculture). Totals of 9 and 14 steroid hormones were detected in water and sediment samples, with concentrations ranging from 0.66 ± 0.17 ng/L to 40.5 ± 5.08 ng/L and from 0.36 ± 0.08 ng/g to 123 ± 19.9 ng/g, respectively. Hazard index (HI) calculations indicated that all sampling locations were identified as medium or high risk for both water and sediment matrices. Nineteen steroids were detected in at least one type of tissue, with the concentrations in the bile, plasma, muscle, liver, and gill ranging from <LOQ to 52.6 ± 4.82 ng/L, from <LOQ to 41.9 ± 4.80 ng/L, from 0.36 ± 0.07 ng/g to 321 ± 19.1 ng/g, from 5000 L/kg). Notably, despite low estimated daily intakes (EDIs) (0.43–6.43 ng/day/person to 18.7 ng/day/person) and hazard quotients (HQs) (below 4.188 × 10⁻⁷), the high bioaccumulation factors (BAFs) underscore the necessity for stringent regulatory measures by local governments. Additionally, a comparison of EDI results across different aquaculture modes and fish species revealed that steroid hormone-related health risks to humans are influenced by both the fish species and the aquaculture mode. This study indicated that the consumption of poly-cultured fish (e.g., bighead carp) may pose a greater steroid-related health risk, compared to the consumption of mono-cultured fish.

The tri-spine horseshoe crab, Tachypleus tridentatus, is an evolutionarily ancient marine chelicerate of considerable ecological and conservation importance in the Indo-West Pacific. Although several mitochondrial genomes have been reported, comprehensive comparative mitogenomic analyses encompassing all extant limulid genera remain limited. In this study, we sequenced and characterized the complete mitochondrial genome of an F1 Tachypleus tridentatus individual derived from wild-caught broodstock from the Beibu Gulf, northern South China Sea, and subsequently maintained at an aquaculture facility, using high-throughput sequencing, and performed an integrated comparative mitogenomic analysis across the three extant genera of Limulidae. The circular mitochondrial genome was 15,006 bp in length and contained the typical set of 37 mitochondrial genes, including 13 protein-coding genes (PCGs), 22 transfer RNA genes, and two ribosomal RNA genes. The newly sequenced Tachypleus tridentatus mitogenome showed highly conserved genome organization and nucleotide composition relative to previously published conspecific mitogenomes, confirming established mitochondrial characteristics of the species. The principal contribution of this study is the addition of a complete Beibu Gulf mitogenome and its integration with 12 additional complete mitochondrial genomes representing all extant limulid species, together with four mitochondrial markers, K2P genetic-distance analyses, and independent BI and ML phylogenetic reconstruction. The concordance among these mitochondrial datasets provides an integrated assessment of genetic divergence and mitochondrial phylogenetic relationships within Limulidae and expands the geographic representation of complete mitochondrial genomic resources for Tachypleus tridentatus.

Acartiidae are often among the most dominant and ecologically critical copepod groups in estuarine pelagic food webs. Here, we sequenced and characterized the complete mitochondrial genome of Acartiella sinensis, representing the first mitogenome for the family Acartiidae. The circular genome is 14,368 bp in length and exhibits a strong A+T bias (79.7%) and a compact organization, with all genes encoded on the heavy strand. Codon usage exhibits a preference for A/U-ending codons, while tRNA secondary structure analysis reveals two serine tRNAs lacking DHU arms and several G–U mismatches. Comparative analysis across 29 copepod mitogenomes indicates a distinctive gene arrangement in A. sinensis, particularly a reversal of Cytb and NAD3 with local tRNA rearrangements. Phylogenetic analyses based on concatenated sequences of 13 protein-coding genes recover A. sinensis as sister to the clade comprising Labidocera rotunda (Pontellidae) and Eurytemora affinis (Temoridae), supporting close evolutionary relationships among these calanoid lineages. Our study provides fundamental genomic information for A. sinensis and contributes to the understanding of mitochondrial genome evolution and phylogenetic relationships within Calanoida.