Mercury in a marine trophic chain

Behavioural and brain biomarker responses in yellowfin bream (Acanthopagrus australis) after inorganic mercury ingestion

To assess the effects of inorganic mercury ingestion on fish general behaviour and brain biochemical markers (acetylcholinesterase - AChE; lipid peroxidation - LPO; glutathione S-transferase - GST; catalase - CAT), juvenile yellowfin bream (Acanthopagrus australis) were fed mercury dosed food (low = 0.7 mg kg^-1, medium = 2.4 mg kg^-1 and high = 6 mg kg^-1) or undosed food (control = 0.2 mg kg^-1) for up to 16 days (5 replicates per treatment). Behavioural indicators, LPO levels and GST activity significantly changed overtime, but were not affected by mercury concentration. In contrast, CAT activity was higher in exposed fish in comparison to controls after 4 days, but not after 8 and 16 days. An additional depuration treatment was evaluated and fish from this treatment were less active and had significantly lower LPO levels and CAT activity than fish constantly exposed to the medium treatment. Overall, results from the present study indicate that a diet containing inorganic mercury impaired yellowfin bream growth and initially affected fish brain CAT activity, however fish were able to recover even with continuous exposure.

Effects of oral exposure to inorganic mercury on the feeding behaviour and biochemical markers in yellowfin bream (Acanthopagrus australis)

Mercury is a known toxic metal, but studies on the effects of inorganic mercury ingestion in aquatic organisms are scarce. The present study aimed to investigate changes in feeding behaviour and biomarkers (lipid peroxidation, acetylcholinesterase, glutathione S-transferase and catalase activities) of yellowfin bream (Acanthopagrus australis) after ingestion of inorganic mercury (control: 0.2 mg kg^-1, low: 0.7 mg kg^-1, medium: 2.4 mg kg^-1 and high: 6 mg kg^-1) over 16 days. After 4 days, exposed fish attempted feeding more often, and showed a significantly lower eating success than controls. However, these differences became less notable with longer exposure periods. Most biochemical markers varied over time, regardless of mercury treatment. However, biomarker responses to mercury were also observed, mostly with increased exposure period and were dependant on the tissue analysed. This study showed that fish can recover from initial feeding behaviour effects of inorganic mercury, but showed delayed response in tissue biomarkers.

Responses of a free-living marine nematode community to mercury contamination: results from microcosm experiments

A microcosm experiment was used to examine the effects of mercury contamination on a free-living nematode community in a Tunisian lagoon. Sediments were contaminated with three mercury concentrations (low, 0.084 ppm; medium, 0.167 ppm; and high, 0.334 ppm), and effects were examined after 60 days. Results from multiple-comparison tests showed significant differences between nematode assemblages from undisturbed control and those from mercury treatments. Most univariate measures decreased significantly with increasing level of Hg contamination. Results from multivariate analyses of the species abundance data demonstrated that responses of nematode species to mercury contamination were varied: Araeolaimus bioculatus was eliminated at all the mercury doses tested and seemed to be an intolerant species to mercury contamination; Marylynnia stekhoveni increased at low and medium concentrations and appeared to be an "opportunistic" species at these doses, whereas Prochromadorella neapolitana, which increased at all doses tested (0.084, 0.167, and 0.334 ppm), seemed to be a "mercury-resistant" species.

Multiple experimental approaches of immunotoxic effects of mercury chloride in the blue mussel, Mytilus edulis, through in vivo, in tubo and in vitro exposures

Biological impairments due to mercury discharge into the environment are now an issue of global concern. From the three forms of mercury found in aquatic ecosystems, the immunotoxic effects of mercury chloride were examined in the model animal, the blue mussel. In order to investigate the toxic potency of this chemical, three exposure regimes were carried out: chronic exposure of groups of individuals, a new protocol "in tubo" designed for sub-acute exposures of individuals, and acute exposures of target cells. Chronic exposure revealed significant immunotoxic effects after 7 days at 10(-6)M, while acute exposures showed significant inhibition of phagocytosis at 10(-4)M and 10(-3)M. In sub-acute exposures both circulating haemocytes and haemocyte mortality increased at 10(-4)M and 10(-3)M while phagocytosis and the clearance rate drew hormetic toxic effects on healthy individuals. These results suggest the use of the "in tubo" design for bivalve toxicological individual studies.

Toxicity of mercury during the embryonic development of Chasmagnathus granulatus (Brachyura, Varunidae)

Ovigerous females of the estuarine crab Chasmagnathus granulatus were exposed to mercury (0.1mg/L) during the entire, early, or late embryonic development. A delay in the egg incubation period and some morphological abnormalities were detected in larvae hatched from exposed females. Particularly, hypopigmentation of body chromatophores was the abnormality that showed the highest incidence, this incidence being greater when ovigerous females were exposed to mercury either during the totality or just the first half of the egg incubation period. In contrast, the effect of mercury on the morphology and pigmentation of eyes was greater when the exposure comprised the totality or just the second half of the incubation period. These results correlate with the timing of both body pigment synthesis and eye formation during embryonic development. Although these abnormalities have been observed in the same species with other heavy metals, such as zinc and copper, the responsiveness during the early and late embryonic development was different with mercury.