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Microcystin-LR (MC-LR) is regarded as one of the most toxic microcystins (MCs) isoforms. Microcystins could cause multiple organs dysfunction, and more attention has been drawn to the toxic effects on the gastrointestinal disorder. By using ex vivo everted gut sac model in 6 fish (Carassius auratus, Megalobrama amblycephala, Hypophthalmichthys molitrix, Aristichthys nobilis, Ctenopharyngodon idellus and Cyprinus carpio) and determining the accumulation of MC-LR in zebrafish intestine, we found a dose-dependent manner in the absorption and accumulation of MC-LR. Until now, little studies have been reported concerning the gut microbiota composition caused by different MC-LR exposure. The present study is the first time characterized the phylogenetic composition and taxonomic of the bacterial communities growth in the intestines of zebrafish treated with MC-LR using 16S rRNA pyrosequencing. After 30 days of treatment with 0, 1, 5 or 20 μg/L MC-LR, the alpha and beta diversity did not generate significant differences, indicating the existence of a core microbiota. However, db-RDA analysis showed that treatment with 20 μg/L MC-LR changed the characteristics of high abundances microbiota. The expression of Oatp2b1, stress related enzyme activities in gut and their associations with gut microbiota were also determined. The identified phylotypes including Actinobacteria, Lactobacillus and some opportunistic pathogens highlight the increasing risks of pathogen invasion and recovery tendency via potential probiotics resistance in zebrafish exposed to MC-LR.

Background: Toxic cyanobacterial blooms result in the production of an organic biomass containing cyanotoxins (e.g. microcystins) and an elevated ammonia concentration in the water environment. The ingestion of toxic cyanobacteria and exposure to ammonia are grave hazards for fish. The present study assessed the effects of dietary toxic cyanobacteria and ammonia exposure on the flesh quality of blunt snout bream (Megalobrama amblycephala).; Results: Dietary toxic cyanobacteria and ammonia exposure had no impact on fish growth performance, fillet proximate composition and drip loss, whereas it significantly decreased fillet total amino acids, total essential amino acids, hardness and gumminess, and increased fillet ultimate pH as well as malondialdehyde content. However, there was no significant interaction between dietary toxic cyanobacteria and ammonia exposure on these parameters. Additionally, dietary toxic cyanobacteria significantly increased fillet initial pH, thaw loss and protein carbonyl content, whereas ammonia exposure did not.; Conclusion: The results of the present study indicate that dietary toxic cyanobacteria and ammonia exposure reduced the quality of blunt snout bream fillet. © 2016 Society of Chemical Industry.; © 2016 Society of Chemical Industry.

While microcystins (MCs) have been reported to exert reproductive toxicity on fish with a sex-dependent effect, the underlying mechanism has been rarely investigated. In the present study, zebrafish were exposed to 1, 5 and 20 μg/L MC-LR for 30 d. The gonad-somatic index declined in all treated males. 17β-estradiol (E2), testosterone (T), 11-keto testosterone (11-KT) and follicle-stimulating hormone (FSH) levels increased in serum from all treated females, while T, FSH and luteinizing hormone (LH) levels changed in all treated males. Histomorphological observation showed that MC-LR exposure evidently retarded oogenesis and spermatogenesis. Transcriptional changes of 22 genes of the hypothalamic-pituitary-gonad (HPG) axis exhibited sex-specific responses and the relationship between gene transcriptions and gametogenesis was evaluated by principle component analysis (PCA). Major contributors to PC1 (gnrh2, gnrhr3, ar, lhr, hmgra, hmgrb and cyp19a) were positively correlated with the number of post-vitellogenic oocytes, while PC1 (gnrh2, lhβ, erβ, fshr, cyp11a and 17βhsd) were positively correlated with the number of spermatozoa. The protein levels of 17βHSD and CYP19a were affected in both females and males. In conclusion, this study first investigated the sex-dependent effects of microcystins on fish reproduction and revealed some important molecular biomarkers related to gametogenesis in zebrafish suffered from MC-LR.

Cyanobacterial blooms caused by water eutrophication have become a worldwide problem. Microcystins (MCs), especially microcystin-LR (MC-LR), released during cyanobacterial blooms exert great toxicity on fish and even lead to massive death. The present study mainly investigated the pathological damage and immune response of spleen, gut and gill in zebrafish exposed to MC-LR. Fish were exposed to 0, 1, 5 and 20 μg/L of MC-LR for 30 d. In zebrafish exposed to 5 and 20 μg/L MC-LR, edematous mitochondria, deformation of the nucleus and compaction of chromatin were observed in lymphocyte of spleen; frayed gut villi, exfoliation of epithelial cells and widespread cell lyses were observed in intestines; hyperemia in gill lamellae, epithelial tissue edema and uplift and lamellar fusion were observed in gill. Varied changed gene expression was observed in spleen, intestine and gill of zebrafish. The transcriptional levels of IFN-1 and IL-8 in spleen significantly up-regulated in 20 μg/L group, and the transcription of IL-1β and TNFα in spleen increased in 1 μg/L MC-LR treated fish. In addition, the mRNA levels of IFN-1, IL-1β, IL-8, TGF-β and TNF-α dramatically increased in intestine and gill in all MC-LR treated groups. The present studies indicated that MC-LR exposure caused marked pathological damage, however, fish could adjust actively the expression of innate immune-related genes to resist the tissue damage. Our findings provided strong evidence of the recovery potential of fish exposed to microcystins.

Toxic cyanobacterial blooms result in the production of an organic biomass containing cyanotoxins (e.g. microcystins) and an elevated ammonia concentration in the water environment. The ingestion of toxic cyanobacteria and exposure to ammonia are grave hazards for fish. The present study assessed the effects of dietary toxic cyanobacteria and ammonia exposure on the flesh quality of blunt snout bream (Megalobrama amblycephala).Dietary toxic cyanobacteria and ammonia exposure had no impact on fish growth performance, fillet proximate composition and drip loss, whereas it significantly decreased fillet total amino acids, total essential amino acids, hardness and gumminess, and increased fillet ultimate pH as well as malondialdehyde content. However, there was no significant interaction between dietary toxic cyanobacteria and ammonia exposure on these parameters. Additionally, dietary toxic cyanobacteria significantly increased fillet initial pH, thaw loss and protein carbonyl content, whereas ammonia exposure did not.The results of the present study indicate that dietary toxic cyanobacteria and ammonia exposure reduced the quality of blunt snout bream fillet. © 2016 Society of Chemical Industry.