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The intensification of production practices in the aquaculture industry has led to the indiscriminate use of antibiotics to combat diseases and reduce costs, which has resulted in environmental pollution, posing serious threats to aquaculture sustainability and food safety. However, the toxic effect of florfenicol (FF) exposure on the hepatopancreas of crustaceans remains unclear. Herein, by employing Chinese mitten crab (Eriocheir sinensis) as subjects to investigate the toxic effects on histopathology, oxidative stress, apoptosis and microbiota of hepatopancreas under environment-relevant (0.5 and 5 μg/L), and extreme concentrations (50 μg/L) of FF. Our results revealed that the damage of hepatopancreas tissue structure caused by FF exposure in a dose-and time-dependent manner. Combined with the increased expression of apoptosis-related genes (Caspase 3, Caspase 8, p53, Bax and Bcl-2) at mRNA and protein levels, activation of catalase (CAT) and superoxide dismutase (SOD), and malondialdehyde (MDA) accumulation, FF exposure also induced oxidative stress, and apoptosis in hepatopancreas. Interestingly, 7 days exposure triggered more pronounced toxic effect in crabs than 14 days under environment-relevant FF concentration. Integrated biomarker response version 2 (IBRv2) index indicated that 14 days FF exposure under extreme concentration has serious toxicity effect on crabs. Furthermore, 14 days exposure to FF changed the diversity and composition of hepatopancreas microbiota leading remarkable increase of pathogenic microorganism Spirochaetes following exposure to 50 μg/L of FF. Taken together, our study explained potential mechanism of FF toxicity on hepatopancreas of crustaceans, and provided a reference for the concentration of FF to be used in culture of Chinese mitten crab.

The intensification of production practices in the aquaculture industry has led to the indiscriminate use of antibiotics to combat diseases and reduce costs, which has resulted in environmental pollution, posing serious threats to aquaculture sustainability and food safety. However, the toxic effect of florfenicol (FF) exposure on the hepatopancreas of crustaceans remains unclear. Herein, by employing Chinese mitten crab (Eriocheir sinensis) as subjects to investigate the toxic effects on histopathology, oxidative stress, apoptosis and microbiota of hepatopancreas under environment-relevant (0.5 and 5 μg/L), and extreme concentrations (50 μg/L) of FF. Our results revealed that the damage of hepatopancreas tissue structure caused by FF exposure in a dose-and time-dependent manner. Combined with the increased expression of apoptosis-related genes (Caspase 3 , Caspase 8 , p53 , Bax and Bcl-2) at mRNA and protein levels, activation of catalase (CAT) and superoxide dismutase (SOD), and malondialdehyde (MDA) accumulation, FF exposure also induced oxidative stress, and apoptosis in hepatopancreas. Interestingly, 7 days exposure triggered more pronounced toxic effect in crabs than 14 days under environment-relevant FF concentration. Integrated biomarker response version 2 (IBRv2) index indicated that 14 days FF exposure under extreme concentration has serious toxicity effect on crabs. Furthermore, 14 days exposure to FF changed the diversity and composition of hepatopancreas microbiota leading remarkable increase of pathogenic microorganism Spirochaetes following exposure to 50 μg/L of FF. Taken together, our study explained potential mechanism of FF toxicity on hepatopancreas of crustaceans, and provided a reference for the concentration of FF to be used in culture of Chinese mitten crab. [Display omitted] • FF induced histology damage, oxidative stress and apoptosis in crab hepatopancreas. • 7 days FF exposure had more pronounced toxic effect on hepatopancreas than 14 days. • Spirochaetes dominated hepatopancreatic microbiota after high level FF exposure. [ABSTRACT FROM AUTHOR]

Symbiotic microorganisms in the hepatopancreas have been found in various crustaceans, and their vital role in maintaining host health has drawn increasing attention. However, the information about the symbiotic microbiota in the hepatopancreas of freshwater crayfish (Procambarus clarkii) is scarce. In this study, the high-throughput sequencing technology was used to characterize the bacterial communities in the hepatopancreas of P. clarkii at different health statuses, including healthy, anorexic, moribund, and whitish muscle statuses. Results showed that the hepatopancreatic microbiota of healthy crayfish was dominated by the phyla Firmicutes, Proteobacteria, and Bacteroidota and Clostridium sensu stricto 11, Proteus , C. sensu stricto 1, Paraclostridium , and Weissella. Distinct differences were found in the structure, composition, and predicted function of the hepatopancreatic microbiota between the healthy and the sick crayfish. The LEfSe analysis revealed that the symbiotic bacterial species, including Proteus penneri , C. sensu stricto 11 and Lactococcus garvieae , and the potential probiotics, such as Weissella cibaria and Lactobacillus murinus, in the hepatopancreas of healthy crayfish were significantly enriched than those of sick crayfish, whereas the opportunistic pathogens, including Citrobacter freundii , Plesiomonas shigelloides , C. sensu stricto 7, and Terrisporobacter , in the hepatopancreas of sick crayfish were significantly enriched than those of healthy crayfish. In addition, compared with that of healthy crayfish, the hepatopancreas of moribund crayfish had significantly enriched bacterial genera, such as Dubosiella , Candidatus , Bacilloplasma , and Phreatobacter , whereas the hepatopancreas of crayfish with whitish muscle disease was observed with a significant enrichment of some opportunistic pathogens, including Morganella morganii , Providencia alcalifaciens , Vagococcus fluvialis , Clostridium lundense , and Bacteroides. This apparent dysbiosis, which showed the increase in opportunistic pathogens and the decrease in symbiotic microorganisms (including potential probiotics), might represent a specific microbial signature of disease occurrence. Furthermore, the PICRUSt2 analysis revealed that the microbial functions involved in carbohydrate metabolism and xenobiotic biodegradation in the hepatopancreas of sick crayfish were significantly enriched than those of healthy crayfish, whereas the microbial functions involved in amino acid metabolism, lipid biosynthesis, biosynthesis of other secondary metabolites, energy metabolism, nucleotide metabolism, transport and catabolism, and immune system in the hepatopancreas of healthy crayfish were significantly enriched compared with those of sick crayfish. This study revealed the hepatopancreatic microbiota dysbiosis associated with disease outbreaks, providing potential indicators for assessing the health status of crayfish and new clues for exploring the potential role of the hepatopancreatic microorganisms in affecting host health and disease. • This study characterized the hepatopancreatic bacterial community of crayfish. • Dysbiosis showed increased opportunistic pathogens and reduced potential probiotics. • Some bacterial indicators were discovered to monitor the health status of crayfish. • Microbial functions mediated by the hepatopancreatic microbiota were investigated. • This study revealed association of the microbiota dysbiosis with disease outbreaks. [ABSTRACT FROM AUTHOR]