Exposure to 17α-Ethinylestradiol Results in Differential Susceptibility of Largemouth Bass (Micropterus salmoides) to Bacterial Infection

Chemical-toxicological insights and process comparison for estrogenic activity mitigation in municipal wastewater treatment plants

Efforts in water ecosystem conservation require an understanding of causative factors and removal efficacies associated with mixture toxicity during wastewater treatment. This study conducts a comprehensive investigation into the interplay between wastewater estrogenic activity and 30 estrogen-like endocrine disrupting chemicals (EEDCs) across 12 municipal wastewater treatment plants (WWTPs) spanning four seasons in China. Results reveal substantial estrogenic activity in all WWTPs and potential endocrine-disrupting risks in over 37.5 % of final effluent samples, with heightened effects during colder seasons. While phthalates are the predominant EEDCs (concentrations ranging from 86.39 %) for both estrogenic activity and major EEDCs (phthalates and estrogens), with the secondary and tertiary treatment segments contributing 88.59 ± 8.12 % and 11.41 ± 8.12 %, respectively. Among various secondary treatment processes, the anaerobic/anoxic/oxic-membrane bioreactor (A/A/O-MBR) excels in removing both estrogenic activity and EEDCs. In tertiary treatment, removal efficiencies increase with the inclusion of components involving physical, chemical, and biological removal principles. Furthermore, correlation and multiple liner regression analysis establish a significant (p < 0.05) positive association between solid retention time (SRT) and removal efficiencies of estrogenic activity and EEDCs within WWTPs. This study provides valuable insights from the perspective of prioritizing key pollutants, the necessity of integrating more efficient secondary and tertiary treatment processes, along with adjustments to operational parameters like SRT, to mitigate estrogenic activity in municipal WWTPs. This contribution aids in managing endocrine-disrupting risks in wastewater as part of ecological conservation efforts.

Hepatic transcriptome profiling of largemouth bass (Micropterus salmoides Lacépède) injected with Flavobacterium covae or lipopolysaccharide

Flavobacterium covae (columnaris) is the most detrimental bacterial disease affecting the largemouth bass (Micropterus salmoides Lacépède) aquaculture industry. In the current study, fish received an intraperitoneal injection of either 1× PBS (100 μL), LPS in PBS (100 μL, 10 μg/mL), or F. covae (100 μL, 2.85 × 1011 CFU/mL) to simulate immunological challenges. After 24 h post-injection, liver tissue from the control and treated groups were then collected for transcriptome analysis. Results of the Gene Ontology (GO) and KEGG pathway analyses for the F. covae and LPS-injected groups found differentially expressed genes (DEGs) enriched primarily in toll-like receptors (TLRs), cytokine-cytokine receptors, complement and coagulation cascades, and the PPAR signalling pathways. This suggests that the liver immune system is enhanced by these five combined pathways. Additionally, the DEGs TLR5, MYD88, and IL-1 were significantly upregulated in F. covae and LPS-injected fish compared to the controls, whereas IL-8 was downregulated. The upregulation of TLR5 was unexpected as F. covae lacks flagellin, the protein that binds to TLR5. Additionally, it is unknown whether the TLR5 is upregulated by LPS. Further research into the upregulation of TLR5 is warranted. These results provide insight into immune responses and associated pathways contributing to the immune system in the liver during columnaris infection and induced response to LPS in largemouth bass.

Declines in Reproductive Condition of Male Largemouth Bass (Micropterus salmoides) Following Seasonal Exposure to Estrogenic Endocrine-Disrupting Compounds

Reproductive abnormalities, that could lead to possible effects at the population level, have been observed in wild fish throughout the United States, with high prevalence in largemouth bass (LMB; Micropterus salmoides) and smallmouth bass (Micropterus dolomieu). Estrone (E1) and atrazine (ATR) are common environmental contaminants often associated with agricultural land use. 17alpha-ethinylestradiol (EE2) is a contaminant associated with wastewater treatment effluent, and a representative, well-studied estrogen commonly used for fish toxicity testing. Our objective was to assess whether early gonad recrudescence in adult fish was a period of sensitivity for alterations in reproductive condition and function. Adult male LMB were exposed from post-spawning to early gonad recrudescence to either a mixture of E1 (47.9 ng/L) + ATR (5.4 µg/L), or EE2 (2.4 ng/L) in outdoor experimental ponds. Gonad samples were collected from fish just prior to the start of exposure (July), at the end of the exposure period (December), the following spring just prior to spawning (April), and post spawning (May). Gonadosomatic index (GSI) was significantly reduced in E1 + ATR-exposed and EE2-exposed males compared to control at every post-exposure time point. Reduced sperm count and sperm motility were observed in the mixture treatment (E1 + ATR) compared to the control. Sperm motility was also reduced in the EE2 treatment. These data together indicate that estrogenic endocrine-disrupting compounds can lessen the reproductive condition of adult male LMB, and that effects of exposure during early gonad recrudescence can persist at least through the subsequent spawning cycle.