In this paper, the complete mitogenome sequence of Mugilogobius chulae is reported. The circular mitochondrial DNA of M. chulae is 16,489 bp in length, containing 13 protein-coding genes, 22 tRNAs, 2 rRNAs and 2 non-coding regions (control region and origin of light-strand replication). The overall base composition of M. chulae is 27.8% A, 27.1% T, 16.8% G, 28.3% C. This genome reported here provides a resource for studies on taxonomy and genetics of M. chulae and closely related species.

Polyhalogenated carbazoles (PHCZs) are a class of nitrogen-containing heterocyclic compounds that are widely distributed throughout the marine environment and sediment. These compounds share structural and toxicity similarities with dioxins. However, our understanding of the toxicological effects of PHCZs on marine organisms and their underlying molecular mechanisms remains limited. In this study, we employed the marine model organism Mugilogobius chulae as the experimental subject and selected 2,7-dibromocarbazole (2,7-DBCZ), a compound known for its high toxicity and detection frequency, to conduct both an acute toxicity test and transcriptome analysis on M. chulae embryos. Our findings revealed that the 96 h median lethal concentration (LC₅₀) of 2,7-DBCZ for M. chulae embryos was 174 μg/L, with a median effective concentration (EC₅₀) resulting in pericardial edema deformity of 88.82 μg/L. Transcriptome analysis revealed significant impacts on various systems in M. chulae embryos following exposure to 2,7-DBCZ, including the sensory, cardiovascular, immune, and endocrine systems. Furthermore, this compound perturbed signaling pathways such as phototransduction, protein folding and processing, amino acid metabolism, lipid transport, and exogenous compound metabolism. Notably, transcript abundance of the CYP1A gene associated with the activation of the AhR signaling pathway, similar to dioxin-like compounds, was 18.18 times higher than that in the control group. This observation suggests that M. chulae embryos mount a stress response when exposed to PHCZs. In summary, this study contributes to our understanding of the toxicological implications of PHCZ in marine fish and offers a theoretical foundation for risk assessment and regulatory frameworks for PHCZs in the marine environment.