Impaired behavioural response to alarm substance in rainbow trout exposed to copper nanoparticles.

To date, studies of the toxicity of engineered nanoparticles (NPs) in fish have not fully considered effects on olfactory-mediated behaviours, despite their ecological importance. In this study the effects of copper NPs (Cu NPs) on the anti-predator behavioural responses of juvenile rainbow trout (Oncorhynchus mykiss) to trout alarm substance was investigated. Individual fish were exposed for 12h to a control (no added Cu), 50µgl(-1) of Cu as Cu NPs, or 50µgl(-1) Cu as CuSO4, after which fish behaviours were analyzed in 10min periods before and after the addition of the alarm substance stimulus. The response of control fish to deionised water (negative control, no alarm substance stimulus) was also analyzed. The alarm substance elicited a behavioural response in the control fish characterized by an immediate freeze response and the slower resumption of swimming activity compared to negative controls exposed to the sham deionised water stimuli. In fish exposed to Cu NPs, the behavioural response to alarm substance was eliminated, with no significant difference in behaviours compared to negative controls. In comparison, exposure to 50µgl(-1) Cu as CuSO4 decreased, but did not eliminate the response of fish to alarm substance, which indicated a significantly greater effect of Cu NPs on olfactory mediated behaviours than of the equivalent concentration of Cu as CuSO4. Measurement of total Cu concentrations in the tissues of fish demonstrated no significant accumulation of Cu from any treatment in gill, liver or brain, confirming the effects of Cu NPs, and to a lesser extent CuSO4, on behavioural responses were mostly associated with the interaction of the materials with the external surfaces of the fish. Scanning electron microscopy revealed that Cu as CuSO4 caused a pronounced depletion of ciliated sensory and non-sensory cells in the olfactory rosette surrounding the midline raphe, whereas Cu NPs had no impact on the structure of the rosette. However, exposure to Cu NPs caused a significant increase in the ratio of oxidized to reduced glutathione in brains of fish, indicating some systemic oxidative stress that was not observed in either controls or fish exposed to CuSO4. Overall, the study showed that the olfactory mediated behaviours of fish were potentially more sensitive to Cu NPs than CuSO4 and NPs elicited effects via a mechanism that is distinct from that of the metal salt.

Esterases activity in the axolotl Ambystoma mexicanum exposed to chlorpyrifos and its implication to motor activity.

The axolotl Ambystoma mexicanum is a neotenic salamander considered a good biological model due to its ability to regenerate limbs, tail, brain and heart cells. Nevertheless, severe reduction of A. mexicanum wild populations in the lacustrine area of Xochimilco, the natural habitat of the axolotl, could be related to several environmental pressures as the presence of organophosphate pesticides (OPPs), intensively applied in agricultural activities in Xochimilco. Thus the aim of this study was to evaluate the effect of environmentally realistic chlorpyrifos (CPF) concentrations, a OPP commonly used in this zone, on esterases activity (acetylcholinesterase and carboxylesterase) and bioconcentration of CPF and to relate them with the motor activity of A. mexicanum juveniles. Axolotls were exposed 48 h to 0.05 and 0.1mg CPF/L, and the responses were evaluated at the end of the CPF exposure. Results suggest that CPF is bioconcentrated into axolotls and that the CPF internal concentrations are related with the observed inhibition activity of AChE (>50%) and CbE (≈ 50%). CPF concentration responsible of the inhibition of the 50% of AChE activity (IC50) was estimated in 0.04 mg CPF/L; however IC50 for CbE activity was not possible to calculate since inhibition levels were lower than 50%, results that suggest a higher resistance of CbE enzymatic activity to CPF. However, motor activity was a more sensitive endpoint to CPF poisoning since time that axolotls spent active and walking, frequency and speed of swimming, frequency of prey attack were reduced >90% of control groups. The motor activity alterations in the axolotl could be related with the registered esterases inhibition. Thus important alterations on axolotls were identified even at short time and low concentrations of CPF exposure. Also, it was possible to link biochemical responses as esterases activity with higher levels of biological organization as behavior. This study provides tools for the regulation of the use of organophosphorus pesticides in the natural habitat of the axolotl.

Filtration rate, assimilation and assimilation efficiency in Crassostrea virginica (Gmelin) fed with Tetraselmis suecica under cadmium exposure.

Crassostrea virginica is an epibentic filter-feeding bivalve of economical importance in coastal lagoons of the Gulf of Mexico, locations with increasing inputs of heavy metals such as cadmium that have become environmental stressors. In this study, feeding and assimilation of the species were evaluated as physiological indicators of cadmium exposure. For this purpose, the filtration rate (FR), food assimilation (A) and assimilation efficiency (AE) of oysters from the Mandinga Lagoon, Veracruz, Mexico, were examined under sublethal and environmentally realistic cadmium concentrations (95 and 170 micro gCd L(-1)). Semi-static, 12-day bioassays were conducted with organisms placed into individual chambers and fed daily with Tetraselmis suecica. FR was calculated by measuring the depletion in algal density. Caloric contents of food and feces produced were also obtained. Condition Index (CI) and morphometric parameters were evaluated at the beginning and at the end of the assay. Total cadmium concentrations were quantified in water and tissue, and the metal bioconcentration factor (BCF) was calculated. Cadmium exposure significantly reduced FR in oysters (mean value: 0.64 L h(-1) and 0.44 L h(-1)) from control values (1.17 L h(-1)). Extreme values among results demonstrate the existence of a high FR (over 4 L h(-1)) mainly in control oysters, and this was associated with a better physiological condition; a low FR (under 2.5 L h(-1)) indicated metabolic stress as a consequence of Cd exposure. A and AE were significantly modified due to cadmium external levels, and time of exposure. FR and A were linearly related, and both decreased as metal BCF increased. Cadmium bioaccumulation was linearly related with external metal levels. The physiological deterioration of native C. virginica from Mandinga Lagoon was reflected in the alteration of FR, A and AE due to cadmium exposure in concentrations considered sublethal, lowering the feeding and assimilation capability of the organisms. The weight loss and mortality recorded in the oysters exposed to the highest metal concentration, was the final consequence of the overall adverse effect of cadmium exposure.