Microcystin-LR stabilizes c-myc protein by inhibiting protein phosphatase 2A in HEK293 cells

Microcystin-LR is the most toxic and the most frequently encountered toxin produced by the cyanobacteria in the contaminated aquatic environment. Previous studies have demonstrated that Microcystin-LR is a potential carcinogen for animals and humans, and the International Agency for Research on Cancer has classified Microcystin-LR as a possible human carcinogen. However, the precise molecular mechanisms of Microcystin-LR-induced carcinogenesis remain a mystery. C-myc is a proto-oncogene, abnormal expression of which contributes to the tumor development. Although several studies have demonstrated that Microcystin-LR could induce c-myc expression at the transcriptional level, the exact connection between Microcystin-LR toxicity and c-myc response remains unclear. In this study, we showed that the c-myc protein increased in HEK293 cells after exposure to Microcystin-LR. Coexpression of protein phosphatase 2A and two stable c-myc protein point mutants (either c-myc(T58A) or c-myc(562A)) showed that Microcystin-LR increased c-myc protein level mainly through inhibiting protein phosphatase 2A activity which altered the phosphorylation status of serine 62 on c-myc. In addition, we also showed that Microcystin-LR could increase c-myc promoter activity as revealed by luciferase reporter assay. And the TATA box for P1 promoter of c-myc might be involved. Our results suggested that Microcystin-LR can stimulate c-myc transcription and stabilize c-myc protein, which might contribute to hepatic tumorigenesis in animals and humans. (C) 2014 Elsevier Ireland Ltd. All rights reserved.Microcystin-LR is the most toxic and the most frequently encountered toxin produced by the cyanobacteria in the contaminated aquatic environment. Previous studies have demonstrated that Microcystin-LR is a potential carcinogen for animals and humans, and the International Agency for Research on Cancer has classified Microcystin-LR as a possible human carcinogen. However, the precise molecular mechanisms of Microcystin-LR-induced carcinogenesis remain a mystery. C-myc is a proto-oncogene, abnormal expression of which contributes to the tumor development. Although several studies have demonstrated that Microcystin-LR could induce c-myc expression at the transcriptional level, the exact connection between Microcystin-LR toxicity and c-myc response remains unclear. In this study, we showed that the c-myc protein increased in HEK293 cells after exposure to Microcystin-LR. Coexpression of protein phosphatase 2A and two stable c-myc protein point mutants (either c-myc(T58A) or c-myc(562A)) showed that Microcystin-LR increased c-myc protein level mainly through inhibiting protein phosphatase 2A activity which altered the phosphorylation status of serine 62 on c-myc. In addition, we also showed that Microcystin-LR could increase c-myc promoter activity as revealed by luciferase reporter assay. And the TATA box for P1 promoter of c-myc might be involved. Our results suggested that Microcystin-LR can stimulate c-myc transcription and stabilize c-myc protein, which might contribute to hepatic tumorigenesis in animals and humans. (C) 2014 Elsevier Ireland Ltd. All rights reserved

Can Hydrodynamics Change Phosphorus Strategies of Diatoms?-Nutrient Levels and Diatom Blooms in Lotic and Lentic Ecosystems

Diatom blooms occur in many water bodies worldwide, causing significant ecological and social concerns. In order to understand the mechanisms of diatom blooms formation, the effects of varying phosphorus (P) concentration and hydrodynamics on the growth of diatoms were studied by combining results from field observations and laboratory experiments. The field investigation showed that spring diatom blooms (Cyclotella meneghiniana and Stephanodiscus hantzschii) occurred in Lake Taihu and Hanjiang River with similar environmental factors such as water temperature, pH, and dissolved oxygen in 2008. Concentrations of total phosphorus (TP), total nitrogen, and ammonia nitrogen (NH4-N) in Lake Taihu were significantly higher than the concentrations in the Hanjiang River. Laboratory experiments were conducted to evaluate growth and physiological responses of four lotic diatoms (Cyclotella atomus, Fragilaria crotonensis, Nitzschia palea, and S. hantzschii, isolated from the Hanjiang River) and three lentic diatoms (C. meneghiniana, Melosira varians, and Stephanodiscus minutulus, isolated from Lake Taihu, Lake Donghu, and Guanqiao Pond, respectively) to various P concentrations under small-scale turbulent and standing conditions. Our results showed that, with turbulence, lotic diatoms C. atomus, F. crotonensis, N. palea, and S. hantzschii demonstrated a significant increase in affinity for P compared with lentic diatoms C. meneghiniana, M. varians, and S. minutulus. Moreover, lotic diatoms C. atomus, F. crotonensis, and N. palea had higher growth rates and photosynthetic efficiencies with small-scale turbulence than with standing conditions both in P-limited and P-replete conditions. Lotic species S. hantzschii and three lentic diatoms (C. meneghiniana, M. varians, and S. minutulus) grew well under standing conditions. Our results may explain our field observation that the occurrence of diatom blooms in lakes is often associated with higher TP concentrations whereas in rivers, diatom blooms occur at a wide range of TP concentrations under flows. Therefore, different hydrodynamics and nutrient concentrations determined the dominant diatom species, according to their habitat-dependent physiological characteristics.Diatom blooms occur in many water bodies worldwide, causing significant ecological and social concerns. In order to understand the mechanisms of diatom blooms formation, the effects of varying phosphorus (P) concentration and hydrodynamics on the growth of diatoms were studied by combining results from field observations and laboratory experiments. The field investigation showed that spring diatom blooms (Cyclotella meneghiniana and Stephanodiscus hantzschii) occurred in Lake Taihu and Hanjiang River with similar environmental factors such as water temperature, pH, and dissolved oxygen in 2008. Concentrations of total phosphorus (TP), total nitrogen, and ammonia nitrogen (NH4-N) in Lake Taihu were significantly higher than the concentrations in the Hanjiang River. Laboratory experiments were conducted to evaluate growth and physiological responses of four lotic diatoms (Cyclotella atomus, Fragilaria crotonensis, Nitzschia palea, and S. hantzschii, isolated from the Hanjiang River) and three lentic diatoms (C. meneghiniana, Melosira varians, and Stephanodiscus minutulus, isolated from Lake Taihu, Lake Donghu, and Guanqiao Pond, respectively) to various P concentrations under small-scale turbulent and standing conditions. Our results showed that, with turbulence, lotic diatoms C. atomus, F. crotonensis, N. palea, and S. hantzschii demonstrated a significant increase in affinity for P compared with lentic diatoms C. meneghiniana, M. varians, and S. minutulus. Moreover, lotic diatoms C. atomus, F. crotonensis, and N. palea had higher growth rates and photosynthetic efficiencies with small-scale turbulence than with standing conditions both in P-limited and P-replete conditions. Lotic species S. hantzschii and three lentic diatoms (C. meneghiniana, M. varians, and S. minutulus) grew well under standing conditions. Our results may explain our field observation that the occurrence of diatom blooms in lakes is often associated with higher TP concentrations whereas in rivers, diatom blooms occur at a wide range of TP concentrations under flows. Therefore, different hydrodynamics and nutrient concentrations determined the dominant diatom species, according to their habitat-dependent physiological characteristics

Impairment of the Mitochondrial Oxidative Phosphorylation System and Oxidative Stress in Liver of Crucian Carp (Carassius auratus L.) Exposed to Microcystins

Hepatotoxic microcystins (MCs) are produced by cyanobacteria in diverse water bodies and the pathophysiology includes induction of reactive oxygen species and adenosine triphosphate (ATP) depletion in cells. In this study, we evaluated MCs induced changes in the oxidative phosphorylation (OXPHOS) system in mitochondria of crucian carp liver. Fish were subdivided into two groups that were intraperitoneally injected with two doses of MCs (50 and 200 MC-LReq g/kg bw) and were sacrificed at 1, 3, 12, 24, and 48 h postinjection. The activities of five enzyme complexes of electron transport chain and mRNA expression of mitochondrial-encoded genes (cox1, cox2, cox3, and atp6) were significantly reduced in a time-dependent pattern after injection. There were also changes in mitochondrial ultrastructure, decreases in ATPase activities and reduction in antioxidant level after MCs exposure. Disorder in the OXPHOS system and decreased activities of antioxidative enzymes might contribute to bioenergy deficiency and consequent hepatocyte damage induced by MCs. (c) 2011 Wiley Periodicals, Inc. Environ Toxicol 29: 30-39, 2014.Hepatotoxic microcystins (MCs) are produced by cyanobacteria in diverse water bodies and the pathophysiology includes induction of reactive oxygen species and adenosine triphosphate (ATP) depletion in cells. In this study, we evaluated MCs induced changes in the oxidative phosphorylation (OXPHOS) system in mitochondria of crucian carp liver. Fish were subdivided into two groups that were intraperitoneally injected with two doses of MCs (50 and 200 MC-LReq g/kg bw) and were sacrificed at 1, 3, 12, 24, and 48 h postinjection. The activities of five enzyme complexes of electron transport chain and mRNA expression of mitochondrial-encoded genes (cox1, cox2, cox3, and atp6) were significantly reduced in a time-dependent pattern after injection. There were also changes in mitochondrial ultrastructure, decreases in ATPase activities and reduction in antioxidant level after MCs exposure. Disorder in the OXPHOS system and decreased activities of antioxidative enzymes might contribute to bioenergy deficiency and consequent hepatocyte damage induced by MCs. (c) 2011 Wiley Periodicals, Inc. Environ Toxicol 29: 30-39, 2014

Genomic Profiling of MicroRNAs and Proteomics Reveals an Early Molecular Alteration Associated with Tumorigenesis Induced by MC-LR in Mice

Studies have demonstrated that microcystins (MCs) can act as potential carcinogens and have caused serious risk to public environmental health. The molecular mechanisms of MC-induced susceptibility to carcinogenesis are largely unknown. In this study, we performed for the first time a comprehensive analysis of changes in microRNAs (miRNAs) and proteins expression in livers of mice treated with MC-LR. Utilizing microarray and two-dimensional gel electrophoresis (2-DE) analysis, we identified 37 miRNAs and 42 proteins significantly altered. Many aberrantly expressed miRNAs were related to various cancers (e.g., miR-125b, hepatocellular carcinoma; miR-21, leukemia; miR-16, chronic lymphocytic leukemia; miR-192, pituitary adenomas; miR-199a-3p, ovarian cancer; miR-34a, pancreatic cancer). Several miRNAs (e.g., miR-34a, miR-21) and proteins (e.g., TGM2, NDRG2) that play crucial roles in liver tumorigenesis were first found to be affected by MC-LR in mouse liver. MC-LR also altered the expression of a number of miRNAs and proteins involved in several pathways related to tumorigenesis, such as glutathione metabolism, VEGF signaling, and MAPK signaling pathway. Integration of post-transcriptomics, proteomics, and transcriptomics reveals that the networks miRNAs and their potential target genes and proteins involved in had a close association with carcinogenesis. These results provide an early molecular mechanism for liver tumorigenesis induced by MCs.Studies have demonstrated that microcystins (MCs) can act as potential carcinogens and have caused serious risk to public environmental health. The molecular mechanisms of MC-induced susceptibility to carcinogenesis are largely unknown. In this study, we performed for the first time a comprehensive analysis of changes in microRNAs (miRNAs) and proteins expression in livers of mice treated with MC-LR. Utilizing microarray and two-dimensional gel electrophoresis (2-DE) analysis, we identified 37 miRNAs and 42 proteins significantly altered. Many aberrantly expressed miRNAs were related to various cancers (e.g., miR-125b, hepatocellular carcinoma; miR-21, leukemia; miR-16, chronic lymphocytic leukemia; miR-192, pituitary adenomas; miR-199a-3p, ovarian cancer; miR-34a, pancreatic cancer). Several miRNAs (e.g., miR-34a, miR-21) and proteins (e.g., TGM2, NDRG2) that play crucial roles in liver tumorigenesis were first found to be affected by MC-LR in mouse liver. MC-LR also altered the expression of a number of miRNAs and proteins involved in several pathways related to tumorigenesis, such as glutathione metabolism, VEGF signaling, and MAPK signaling pathway. Integration of post-transcriptomics, proteomics, and transcriptomics reveals that the networks miRNAs and their potential target genes and proteins involved in had a close association with carcinogenesis. These results provide an early molecular mechanism for liver tumorigenesis induced by MCs

Phytoplankton dynamics and their equilibrium phases in the Yanghe Reservoir, China

Phytoplankton species composition, seasonal dynamics, and spatial distribution were studied during 2009 along with key physical and chemical variables in Yanghe Reservoir, a temperate eutrophic reservoir with a long water residence time of 284days. In the northern part of the reservoir, Microcystis wesenbergii dominated throughout the summer but no steady-state phases were found, as periods of equilibrium lasted for only two weeks each. In the southern part, the first steady-state phase occurred in spring, lasted for four weeks, and was dominated by Cryptomonas erosa. The second phase was dominated by M. wesenbergii in late summer and persisted for four weeks. The results suggest that steady-state phases establish more readily in deep areas with longer residence times and more dominant species compared to shallow areas. Thermal stratification in the deep area and fluctuation of nitrogen and phosphorus concentrations in the shallow area were considered to be responsible for such differences. Canonical correspondence analysis indicated that M. wesenbergii was more strongly related to NOx-N than to temperature in both areas of the reservoir. We conclude that in eutrophic lakes, a high concentration of nutrients such as NOx-N is more important than temperature in the establishment of a steady state.Phytoplankton species composition, seasonal dynamics, and spatial distribution were studied during 2009 along with key physical and chemical variables in Yanghe Reservoir, a temperate eutrophic reservoir with a long water residence time of 284days. In the northern part of the reservoir, Microcystis wesenbergii dominated throughout the summer but no steady-state phases were found, as periods of equilibrium lasted for only two weeks each. In the southern part, the first steady-state phase occurred in spring, lasted for four weeks, and was dominated by Cryptomonas erosa. The second phase was dominated by M. wesenbergii in late summer and persisted for four weeks. The results suggest that steady-state phases establish more readily in deep areas with longer residence times and more dominant species compared to shallow areas. Thermal stratification in the deep area and fluctuation of nitrogen and phosphorus concentrations in the shallow area were considered to be responsible for such differences. Canonical correspondence analysis indicated that M. wesenbergii was more strongly related to NOx-N than to temperature in both areas of the reservoir. We conclude that in eutrophic lakes, a high concentration of nutrients such as NOx-N is more important than temperature in the establishment of a steady state

Decrease of NH4+-N by bacterioplankton accelerated the removal of cyanobacterial blooms in aerated aquatic ecosystem

We used aerated systems to assess the influence of the bacterioplankton community on cyanobacterial blooms in algae/post-bloom of Lake Taihu, China. Bacterioplankton community diversity was evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. Chemical analysis and nitrogen dynamic changes illustrated that NH4+-N was nitrified to NO2--N and NO3--N by bacterioplankton. Finally, NH4+-N was exhausted and NO3--N was denitrified to NO2--N, while the accumulation of NO2--N indicated that bacterioplankton with completely aerobic denitrification ability were lacking in the water samples collected from Lake Taihu. We suggested that adding completely aerobic denitrification bacteria (to denitrify NO2--N to N-2) would improve the water quality. PCR-DGGE and sequencing results showed that more than 1/3 of the bacterial species were associated with the removal of nitrogen, and Acidovorax temperans was the dominant one. PCR-DGGE, variation of nitrogen, removal efficiencies of chlorophyll-a and canonical correspondence analysis indicated that the bacterioplankton significantly influenced the physiological and biochemical changes of cyanobacteria. Additionally, the unweighted pair-group method with arithmetic means revealed there was no obvious harm to the microecosystem from aeration. The present study demonstrated that bacterioplankton can play crucial roles in aerated ecosystems, which could control the impact of cyanobacterial blooms in eutrophicated fresh water systems.We used aerated systems to assess the influence of the bacterioplankton community on cyanobacterial blooms in algae/post-bloom of Lake Taihu, China. Bacterioplankton community diversity was evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. Chemical analysis and nitrogen dynamic changes illustrated that NH4+-N was nitrified to NO2--N and NO3--N by bacterioplankton. Finally, NH4+-N was exhausted and NO3--N was denitrified to NO2--N, while the accumulation of NO2--N indicated that bacterioplankton with completely aerobic denitrification ability were lacking in the water samples collected from Lake Taihu. We suggested that adding completely aerobic denitrification bacteria (to denitrify NO2--N to N-2) would improve the water quality. PCR-DGGE and sequencing results showed that more than 1/3 of the bacterial species were associated with the removal of nitrogen, and Acidovorax temperans was the dominant one. PCR-DGGE, variation of nitrogen, removal efficiencies of chlorophyll-a and canonical correspondence analysis indicated that the bacterioplankton significantly influenced the physiological and biochemical changes of cyanobacteria. Additionally, the unweighted pair-group method with arithmetic means revealed there was no obvious harm to the microecosystem from aeration. The present study demonstrated that bacterioplankton can play crucial roles in aerated ecosystems, which could control the impact of cyanobacterial blooms in eutrophicated fresh water systems

Sources of organic matter affect depth-related microbial community composition in sediments of Lake Erhai, Southwest China

Sediment cores taken from different areas of the mesotrophic Lake Erhai were analysed to investigate the vertical distribution of bacterial community composition (BCC), as well as physicochemical parameters. PCR-denaturing gradient gel electrophoresis (DGGE), stable carbon isotope (delta C-13), C/N atomic ratio and canonical correspondence analysis (CCA) were used to explore the relationships between the succession of bacterial communities and environmental variables, emphasising changes in the sources of organic matter (OM). The BCC in natural environments was characterised by DGGE of the 16S rRNA gene with subsequent sequencing of bands of interest. The CCA revealed that the depth-related variation in sediment bacterial communities in different areas of the lake was significantly influenced by varying environmental factors. The OM source, however, played an important role in structuring BCC at all sites. The DGGE banding patterns revealed that the abundance of Deltaproteobacteria decreased with accompanying elevated levels of C4 plant-derived organic carbon. The sequencing of DGGE bands suggested that the majority of the sequences were affiliated with common phylogenetic groups in lake sediments: Chloroflexi, Deltaproteobacteria and Firmicutes. Betaproteobacteria detected in our study appeared as a prominent phylotype in the upper sediment. The Shannon-Wiener diversity index of bacterial communities was directly affected by the OM source. Constant OM sources resulted in a stable higher diversity of bacterial communities and broader enzymatic capabilities to access OM. We conclude that the differences in the diversity of bacterial communities in sediments differing in their sources of OM were related to environmental variables (e.g. water level, river runoff and terrestrial vegetation composition). Our study provided insights into the relationships between natural BCC and OM sources, facilitating a better understanding of microbial community structure in lake sediment

Seasonal changes in icefish diel feeding patterns in Lake Chaohu, a large shallow eutrophic lake of China

Seasonal changes in the diel feeding patterns of the zooplanktivorous icefish (Neosalanx taihuensis), which is an endemic species of China, were studied in the large, shallow eutrophic Lake Chaohu of China during the autumn of 2002 and summer of 2003. The results of the diel feeding rhythm indicate that icefish is a visual particulate feeder. There were large differences in diet composition and the selection indices of certain prey by icefish. In general, icefish fed more on calanoids than on cyclopoids, and fed more on larger cladocerans (i.e., Daphnia, Moina, Leptodora) than smaller cladocerans (i.e., Bosmina, Ceriodaphnia). Icefish is highly selective of individual food items, with prey selection also being dependent on fish size. There was no significant difference in the prey selection between male and female icefish. This study provides the first report of diel feeding rhythm in icefish, and is the first comparative study on prey selection between male and female icefish.Seasonal changes in the diel feeding patterns of the zooplanktivorous icefish (Neosalanx taihuensis), which is an endemic species of China, were studied in the large, shallow eutrophic Lake Chaohu of China during the autumn of 2002 and summer of 2003. The results of the diel feeding rhythm indicate that icefish is a visual particulate feeder. There were large differences in diet composition and the selection indices of certain prey by icefish. In general, icefish fed more on calanoids than on cyclopoids, and fed more on larger cladocerans (i.e., Daphnia, Moina, Leptodora) than smaller cladocerans (i.e., Bosmina, Ceriodaphnia). Icefish is highly selective of individual food items, with prey selection also being dependent on fish size. There was no significant difference in the prey selection between male and female icefish. This study provides the first report of diel feeding rhythm in icefish, and is the first comparative study on prey selection between male and female icefish

Nephrotoxic effects from chronic toxic cyanobacterial blooms in fishes with different trophic levels in a large Chinese lake

Physiological and biochemical responses in kidneys of fishes with different trophic levels to toxic cyanobacterial blooms were studied. We sampled four fishes: the phytoplanktivorous Hypophthalmichthys molitrix and Aristichthys nobilis, the omnivorous Carassius auratus, and the carnivorous Culter ilishaeformis. Alterations of the antioxidant (GSH) and the major antioxidant enzymes (CAT, SOD, GPx, GST) were monitored monthly. Catalase and glutathione S-transferase were significantly higher during blooms than before and after blooms. All fishes showed ultrastructural alterations during blooms, which mainly are inosculation of foot processes in epithelial cell of glomeruli and mitochondria swelling in the proximal tubules. The results suggested that kidney impairment from chronic exposure of toxic cyanobacterial blooms might be the first step, and then followed by hepatic failure. Compared with livers in terms of physiological status, the weaker antioxidant ability of kidney made it more susceptible to chronic MCs exposure, besides its effective accumulation of MC metabolites. (C) 2011 Elsevier B.V. All rights reserved.Physiological and biochemical responses in kidneys of fishes with different trophic levels to toxic cyanobacterial blooms were studied. We sampled four fishes: the phytoplanktivorous Hypophthalmichthys molitrix and Aristichthys nobilis, the omnivorous Carassius auratus, and the carnivorous Culter ilishaeformis. Alterations of the antioxidant (GSH) and the major antioxidant enzymes (CAT, SOD, GPx, GST) were monitored monthly. Catalase and glutathione S-transferase were significantly higher during blooms than before and after blooms. All fishes showed ultrastructural alterations during blooms, which mainly are inosculation of foot processes in epithelial cell of glomeruli and mitochondria swelling in the proximal tubules. The results suggested that kidney impairment from chronic exposure of toxic cyanobacterial blooms might be the first step, and then followed by hepatic failure. Compared with livers in terms of physiological status, the weaker antioxidant ability of kidney made it more susceptible to chronic MCs exposure, besides its effective accumulation of MC metabolites. (C) 2011 Elsevier B.V. All rights reserved

Role of body size and temporal hydrology in the dietary shifts of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) in a large floodplain lake

Seasonal water-level changes in floodplain lakes can induce variations in primary and secondary production, thus affecting trophic interactions. In this study, we tested the latter by studying size- and temporal hydrology-related shifts in the diet of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) from Lake Poyang. During the wet season, delta C-13 values ranged from -28.2aEuro degrees for small anchovies to -24.6aEuro degrees for larger individuals, but delta N-15 ranged from 18.9aEuro degrees for smaller fish to 12.4aEuro degrees for larger fish. Significant C-13-enrichment and N-15-depletion occurred with increasing size, revealing that different carbon sources were used as the fish grew. Given the high hydrologic fluctuation levels, significant differences in delta C-13 values were observed among larger anchovies between seasons, indicating a temporal dietary shift. Anchovies fed primarily on shrimp and fish during the low-water season despite the predominance of zooplankton during the two seasons studied, which indicated increased piscivorous reliance. C. brachygnathus exhibited higher delta N-15 values during the wet season because the food items were N-15-enriched. Human waste brought by floods could be another possible interpretation. Considering C. brachygnathus is an important link between plankton production and higher piscivorous trophic levels, changes in the species are expected to affect the functioning of lake food webs along the trophic pathway.Seasonal water-level changes in floodplain lakes can induce variations in primary and secondary production, thus affecting trophic interactions. In this study, we tested the latter by studying size- and temporal hydrology-related shifts in the diet of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) from Lake Poyang. During the wet season, delta C-13 values ranged from -28.2aEuro degrees for small anchovies to -24.6aEuro degrees for larger individuals, but delta N-15 ranged from 18.9aEuro degrees for smaller fish to 12.4aEuro degrees for larger fish. Significant C-13-enrichment and N-15-depletion occurred with increasing size, revealing that different carbon sources were used as the fish grew. Given the high hydrologic fluctuation levels, significant differences in delta C-13 values were observed among larger anchovies between seasons, indicating a temporal dietary shift. Anchovies fed primarily on shrimp and fish during the low-water season despite the predominance of zooplankton during the two seasons studied, which indicated increased piscivorous reliance. C. brachygnathus exhibited higher delta N-15 values during the wet season because the food items were N-15-enriched. Human waste brought by floods could be another possible interpretation. Considering C. brachygnathus is an important link between plankton production and higher piscivorous trophic levels, changes in the species are expected to affect the functioning of lake food webs along the trophic pathway