Yafen Chen

Combined effects of ammonia and microcystin on survival, growth, antioxidant responses, and lipid peroxidation of bighead carp Hypophthalmythys nobilis larvae.

Hazardous materials, such as ammonia and microcystin, are released into lakes during cyanobacterial bloom degradation and may severely impact aquatic organisms. To assess the combined effects of ammonia and microcystin on survival, growth, and oxidative stress of larval fish, 14-day-old larvae of bighead carp Hypophthalmythys nobilis were exposed to solutions with different combined concentrations of ammonia (0, 0.06, 0.264mgL(-1)) and microcystin (0, 2, 10, 30μgL(-1)) for 10 days. Microcystin significantly decreased body length, while ammonia significantly increased body weight, specific growth rate, and condition factor, but there was no significant interaction between ammonia and microcystin on them. Superoxide dismutase, catalase, and malondialdehyde significantly changed with microcystin concentration, whereas glutathione was not affected by microcystin. Ammonia significantly affected the antioxidant system. There were significant interactions between ammonia and microcystin on superoxide dismutase and malondialdehyde. Our data clearly demonstrate that ammonia and microcystin adversely affect bighead carp larvae.

The Interactive Effects of Ammonia and Microcystin on Life-History Traits of the Cladoceran Daphnia magna: Synergistic or Antagonistic?

The occurrence of Microcystis blooms is a worldwide concern that has caused numerous adverse effects on water quality and lake ecology. Elevated ammonia and microcystin concentrations co-occur during the degradation of Microcystis blooms and are toxic to aquatic organisms; we studied the relative and combined effects of these on the life history of the model organism Daphnia magna. Ammonia and microcystin-LR treatments were: 0, 0.366, 0.581 mg L−1 and 0, 10, 30, 100 µg L−1, respectively. Experiments followed a fully factorial design. Incubations were 14 d and recorded the following life-history traits: number of moults, time to first batch of eggs, time to first clutch, size at first batch of eggs, size at first clutch, number of clutches per female, number of offspring per clutch, and total offspring per female. Both ammonia and microcystin were detrimental to most life-history traits. Interactive effects of the toxins occurred for five traits: the time to first batch of eggs appearing in the brood pouch, time to first clutch, size at first clutch, number of clutches, and total offspring per female. The interactive effects of ammonia and microcystin appeared to be synergistic on some parameters (e.g., time to first eggs) and antagonistic on others (e.g., total offspring per female). In conclusion, the released toxins during the degradation of Microcystis blooms would result, according to our data, in substantially negative effect on D. magna.

Acute Toxicity of Nitrite and Ammonia to Daphnia similoides of Different Developmental Stages: Using the Modified Gaussian Model to Describe

To gain an insight into the tolerance of Daphnia to nitrite and ammonia, a modified Gaussian model was used to describe the trends of changes in LC50s of nitrite and ammonia to Daphnia similoides at different developmental stages. LC50s of NO2–N and NH3–N increased with age before maturation and then decreased at maturation. A modified Gaussian model provided an accurate fit for the changes in LC50s of NO2–N and NH3–N, in which the parameters have definite biological meanings. From this model, we can gain an insight into the maximum LC50 and the age that has the maximum LC50 and predict LC50s at any specific ages. We suggest that such a model might be used to describe the trend in acute toxicity of some other zooplankton species at different stages.

Aggregate formation and polysaccharide content of Chlorella pyrenoidosa Chick (Chlorophyta) in response to simulated nutrient stress.

To determine how polysaccharide production influences microalgal aggregate size, we stimulated polysaccharide production using existing methods (previously applied to cyanobacteria and plants). Cultures were treated with glyoxylate (0, 0.25, 0.5, 1.25 mmol/L) to simulate nutrient stress and examined for 9 days (approaching stationary phase on day 9) to assess: growth rate, polysaccharide production (soluble, bound, and total), aggregate size, and the relation between polysaccharide and aggregate size. We found: 1.25 mmol/L glyoxylate inhibits growth, but 0.25 and 0.5 mmol/L do not, allowing comparisons of aggregate formation at lower concentrations; glyoxylate-induced polysaccharide production, which increased with increased glyoxylate concentration and time; an increase in relative abundance of cells bound together with increased glyoxylate addition; and increased glyoxylate-stimulated polysaccharide levels were directly correlated with aggregate size. This study indicates that glyoxylate may be used to examine microalgal ecophysiology and offers a method to predict the influence of nutrient stress on polysaccharide production.

The interactive effects of microcystin and nitrite on life-history parameters of the cladoceran Daphnia obtusa

Elevated nitrite and microcystin concentrations co-occur during degradation of Microcystis blooms and are toxic to aquatic organisms. We studied the relative and combined effects of these on Daphnia obtusa life-history. Nitrite and microcystin-LR treatments were: 0, 1, 3 mg L(-1) and 0, 10, 100, 300 μg L(-1), respectively. Experiments were factorial with 12 treatment combinations. Incubations were 15 d and recorded: moult number; time to first batch of eggs; time to first clutch; size at first batch of eggs; size at first clutch; number of clutches per female; number of offspring per clutch; total offspring per female. Interactive effects of the toxins occurred for time to first batch of eggs and time to first clutch. The remaining traits were negatively affected by nitrite: a significant decrease occurred in number of offspring per clutch and total number of offspring per mother (both decreased by ∼ 50%); total clutches per mother; number of moults; mother size at first clutch; and first appearance of eggs (primarily at the highest nitrite concentration). We support the literature, recognising nitrite is toxic, and although Microcystis is toxic to zooplankton, the main threat is not from dissolved microcystin but from degradative products such as nitrite.

Incubation and oxidative stress of grass carp (Ctenopharyngodon idella) embryos exposed to different un-ionized ammonia levels

The increase in concentration of ammonia in surface water is a critical concern in aquaculture, especially in fish larvae production. The purpose of this study was to assess the effects of un-ionized ammonia (NH3) on the development and oxidative stress of grass carp (Ctenopharyngodon idella) embryos. The results showed that the rate of embryonic development to hatch was retarded with an increase in NH3–N concentration. Hatch rate of grass carp embryos in the control was greater than 90%, whereas the hatch rate in 0.879 mg L−1 of NH3–N was less than 70%. Viability of newly hatched larvae (24 h post-hatch) significantly decreased with increasing NH3–N concentrations. Viability of newly hatched larvae 24 h post-hatch in the control was 97.8%, whereas in 0.879 mg L−1 of NH3–N, the viability was only approximately 40%. This indicates that although embryos can hatch to larvae under high NH3–N conditions, the larvae were much less tolerant of NH3–N than embryos. NH3–N had a significant effect on superoxide dismutase (SOD) and malondialdehyde (MDA) levels, whereas there was no statistically significant difference in catalase and glutathione activity among different NH3–N levels. Two-way analysis of variance indicated that there was a statistically significant interaction between NH3–N and developmental stage on SOD and MDA. Such changes indicated the presence of oxidative stress when grass carp embryos were exposed in water containing pollutants and SOD plays a key role in removing the free radicals in this case.

Response of juvenile crucian carp (Carassius auratus) to long-term ammonia exposure: feeding, growth, and antioxidant defenses

We investigated the effect of long-term ammonia exposure on feeding, growth, and some antioxidant parameters of liver, gill, and blood of juvenile crucian carp (Carassius auratus). In chronic exposure experiments, juvenile crucian carp were exposed to different concentrations of NH3–N (0.107, 0.214, 0.321, 0.428 mg L−1) for 45 days. Ammonia in the external environment significantly impaired the feeding and growth of juvenile crucian carp; additionally, enzymatic (superoxide dismutase (SOD) and catalase (CAT)) and non-enzymatic (glutathione (GSH) and malondialdehyde (MDA)) antioxidants in fish liver showed their protective functions significantly when oxidative stress occurred, but specific results were variable depending on time, ammonia concentration, and the tissue.

In situ studies on growth, oxidative stress responses, and gene expression of juvenile bighead carp (Hypophthalmichthys nobilis) to eutrophic lake water dominated by cyanobacterial blooms

Cyanobacterial blooms have received increasing attention as a public biohazard for human and animal health. To assess the effect of cyanobacteria-dominant lake water on juvenile fish, we measured the responses of specific growth rate, condition factor, body weight and body length, oxidative stress, and related gene expression of juvenile bighead carp Hypophthalmichthys nobilis exposed to in situ eutrophic lake (Chl a was around 7.0μgL(-1)). Results showed in situ cyanobacteria-dominant lake water had no effect on the growth performance, but significantly elevated the contents of malondialdehyde, the expression of heat shock protein 70, and the activity of superoxide dismutase, indicating that oxidative stress occurred. Meanwhile in situ lake water significantly decreased the expression of catalase and glutathione S-transferase genes. We conclude that in situ cyanobacteria-dominated lake water was harmful to juvenile bighead carp based on the oxidative stress and changes in the related gene expression levels.

Concentration–response function of nitrite on survival, molting, and reproduction of Daphnia similoides

We assessed the chronic toxicity of nitrite to Daphnia similoides and modeled the concentration–response function of nitrite on survival, molting, and reproduction. Survival time, number of molting, number of total offspring per female, number of broods per female, and number of offspring per brood decreased significantly with increasing NO2–N concentration during the 21-day experiment. The EC50s for number of total offspring per female, number of broods per female, and number of offspring per brood were 1.56, 3.99, and 1.71 mg L−1, respectively. A four-parameter logistic model was suitable for describing the concentration–response function and allows the estimation of reproduction indices of D. similoides at any given concentration of NO2–N.

The effect of nitrogen concentration and its interaction with light intensity on population dynamics and polysaccharide content of Microcystis aeruginosa

Cultures of Microcystis aeruginosa were inoculated into media with different nitrogen concentrations (5%, 10%, 25%, 100% N of standard BG-11 media) and cultured under two light intensities for 35 days. The populations of M. aeruginosa tended to increase with decreased nitrogen concentrations in both the high light intensity and the low light intensity. Cell densities in high light intensity were significantly higher than those in low light intensity under lower nitrogen concentrations (5%, 10%, 25% N), whereas the result was reversed under the high nitrogen concentration (100% N). A four-parameter logistic model fitted all the population dynamics well. Soluble extracellular polysaccharide content of M. aeruginosa cultured in the 100% N media was significantly higher than in M. aeruginosa cultured in the lower nitrogen media; however, the bound polysaccharide and total polysaccharide of M. aeruginosa cultured in 5% N media were significantly higher than those of M. aeruginosa cultured in all other nitrogen concentration media. Significant differences in bound polysaccharide and total polysaccharide were also detected between the high light intensity and the low light intensity. There was a statistically significant interaction between light intensity and nitrogen concentration on the soluble extracellular polysaccharide content but not on bound polysaccharide or total polysaccharide.