The Interactive Effects of the Anti-Sea Lice Pesticide Azamethiphos and Temperature on Oxidative Damage and Antioxidant Responses in the Oyster Ostrea chilensis.

Azamethiphos is used in the salmon industry to treat sea lice and is subsequently discharged into the sea, which may affect non-target species (NTS). A rise in seawater temperature could enhance the sensitivity of NTS. Thus, in the present investigation, the combined effects of azamethiphos (0 µg L-1, 15 µg L-1 and 100 µg L-1) and temperature (12 °C and 15 °C) was assessed over time (7 days) in the gonads and gills of the oyster Ostrea chilensis, assessing its oxidative damage (lipid peroxidation and protein carbonyls) and total antioxidant capacity. Our results indicated that in gonads and gills, lipid peroxidation levels increased over time during exposure to both pesticide concentrations. Protein carbonyl levels in gills increased significantly in all experimental treatments; however, in gonads, only pesticide concentration and exposure time effected a significant increase in protein damage. In both, gill and gonad temperature did not influence oxidative damage levels. Total antioxidant capacity in gonads was influenced only by temperature treatment, whereas in the gills, neither temperature nor azamethiphos concentration influenced defensive responses. In conclusion, our results indicated the time of pesticide exposure (both concentrations) had a greater influence than temperature on the cellular damage in this oyster.

The interactive effect of anti-sea lice pesticide azamethiphos and temperature on the physiological performance of the filter-feeding bivalve Ostrea chilensis: A non-target species.

The pesticide azamethiphos used by the salmon industry to treat sea lice, is applied as a bath and subsequently discharged into the sea. The effects of azamethiphos concentration (0, 15 and 100 µg L-1) on the physiology of the Chilean oyster (Ostrea chilensis) at two temperatures (12 and 15 °C) was examined. In all azamethiphos treatments, oysters kept at 15 °C had clearance rates (CR) higher than oysters kept at 12 °C. The oxygen consumption rate (OCR) increased at higher temperatures, except with 100 µg L-1 of azamethiphos, where no changes were observed. Sixty days after the exposure, survival rates of 91 and 79% (15 and 100 µg L-1, respectively), were observed compared to the controls, a situation independent of the experimental temperature. The interaction between temperature and pesticide has detrimental effects on the physiological performance and survival of O. chilensis, and these effects should also be assessed for other non-target species.

The filter-feeding bivalve Mytilus chilensis capture pelagic stages of Caligus rogercresseyi: A potential controller of the sea lice fish parasites.

The copepod Caligus rogercresseyi is an ectoparasite of several salmonid species. The pumping activity of filter-feeding molluscs could reduce the abundance of copepod dispersive larval stages in the water column. In this research, nauplius II and copepodid larvae of C. rogercresseyi were exposed to filtering mussels (Mytilus chilensis) of different sizes. These mussels were able to filter both larval stages, although they were more efficient in catching nauplius II. The fact that nauplius II were ingested more efficiently could be explained by their smaller size, lower swimming velocity (escape) and longer resting times between movements, when they were exposed to the influx of water around the inhalant area of the mussels. Larger mussels were more effective filtering C. rogercresseyi larvae due to their larger inhalant area and the related water influx. Additionally, the results suggest that larvae captured by the mussels can be incorporated into pseudofaeces or ingested and then released as part of the faeces. Thus, high concentrations of M. chilensis surrounding salmon farms may act as biological barriers, reducing the density of copepod dispersive larval stages and, thus, salmon infestations.

Comparison of Aerobic Scope for Metabolic Activity in Aquatic Ectotherms With Temperature Related Metabolic Stimulation: A Novel Approach for Aerobic Power Budget.

Considering that swim-flume or chasing methods fail in the estimation of maximum metabolic rate and in the estimation of Aerobic Scope (AS) of sedentary or sluggish aquatic ectotherms, we propose a novel conceptual approach in which high metabolic rates can be obtained through stimulation of organism metabolic activity using high and low non-lethal temperatures that induce high (HMR) and low metabolic rates (LMR), This method was defined as TIMR: Temperature Induced Metabolic Rate, designed to obtain an aerobic power budget based on temperature-induced metabolic scope which may mirror thermal metabolic scope (TMS = HMR-LMR). Prior to use, the researcher should know the critical thermal maximum (CT max) and minimum (CT min) of animals, and calculate temperature TIMR max (at temperatures -5-10% below CT max) and TIMR min (at temperatures +5-10% above CT min), or choose a high and low non-lethal temperature that provoke a higher and lower metabolic rate than observed in routine conditions. Two sets of experiments were carried out. The first compared swim-flume open respirometry and the TIMR protocol using Centropomus undecimalis (snook), an endurance swimmer, acclimated at different temperatures. Results showed that independent of the method used and of the magnitude of the metabolic response, a similar relationship between maximum metabolic budget and acclimation temperature was observed, demonstrating that the TIMR method allows the identification of TMS. The second evaluated the effect of acclimation temperature in snook, semi-sedentary yellow tail (Ocyurus chrysurus), and sedentary clownfish (Amphiprion ocellaris), using TIMR and the chasing method. Both methods produced similar maximum metabolic rates in snook and yellowtail fish, but strong differences became visible in clownfish. In clownfish, the TIMR method led to a significantly higher TMS than the chasing method indicating that chasing may not fully exploit the aerobic power budget in sedentary species. Thus, the TIMR method provides an alternative way to estimate the difference between high and low metabolic activity under different acclimation conditions that, although not equivalent to AS may allow the standardized estimation of TMS that is relevant for sedentary species where measurement of AS via maximal swimming is inappropriate.

Differences in the respiratory response to temperature and hypoxia across four life-stages of the intertidal porcelain crab Petrolisthes laevigatus.

For aquatic breathers, hypoxia and warming can act synergistically causing a mismatch between oxygen supply (reduced by hypoxia) and oxygen demand (increased by warming). The vulnerability of these species to such interactive effects may differ during ontogeny due to differing gas exchange systems. This study examines respiratory responses to temperature and hypoxia across four life-stages of the intertidal porcelain crab Petrolisthes laevigatus. Eggs, megalopae, juveniles and adults were exposed to combinations of temperatures from 6 to 18 °C and oxygen tensions from 2 to 21 kPa. Metabolic rates differed strongly across life-stages which could be partly attributed to differences in body mass. However, eggs exhibited significantly lower metabolic rates than predicted for their body mass. For the other three stages, metabolic rates scaled with a mass exponent of 0.89. Mass scaling exponents were similar across all temperatures, but were significantly influenced by oxygen tension (the highest at 9 and 14 kPa, and the lowest at 2 kPa). Respiratory responses across gradients of oxygen tension were used to calculate the response to hypoxia, whereby eggs, megalopae and juveniles responded as oxyconformers and adults as oxyregulators. The thermal sensitivity of the metabolic rates (Q10) were dependent on the oxygen tension in megalopae, and also on the interaction between oxygen tension and temperature intervals in adults. Our results thus provide evidence on how the oxygen tension can modulate the mass dependence of metabolic rates and demonstrate changes in respiratory control from eggs to adults. In light of our results indicating that adults show a good capacity for maintaining metabolism independent of oxygen tension, our study highlights the importance of assessing responses to multiple stressors across different life-stages to determine how vulnerability to warming and hypoxia changes during development.

Lethal and sub-lethal effects of commonly used anti-sea lice formulations on non-target crab Metacarcinus edwardsii larvae.

The pesticides used by the salmon industry to treat sea lice, are applied in situ via a bath solution and are subsequently discharged into the surrounding medium. The effects of cypermethrin, deltamethrin, azamethiphos and hydrogen peroxide were assessed on the performance of Metacarcinus edwardsii larvae, an important crab for Chilean fishery. All larvae were dead or dying after 30 min of exposure to cypermethrin and after 40 min to deltamethrin at concentrations 100 and 20 times lower (0.15 and 0.1 µg L-1, respectively) than the concentrations and exposure times recommended by the manufacturers (CRM) to treat sea lice. Azamethiphos affected all larvae at a concentration 10 times lower than CRM. Hydrogen peroxide had the lowest detrimental effects, but at the CRM, 100% of the larvae were affected. Sub-lethal effects, i.e prolonged developmental time, were observed at concentrations lower than CRM. Repeated exposure to azamethiphos (0.0625-0.5 µg L-1) and hydrogen peroxide (188-1500 mg L-1) had effects on survival. In conclusion, the pesticides used against parasitic copepod tested here, negatively affect non-target crustacean larvae. Due to the product's characteristics, the lethal effects of the pyrethroids probably are restricted to the time and area of application, while the action of azamethiphos may extend to a wider area. Current data are insufficient to accurately dimension the effects of these compounds in the field. More research is required to evaluate the consequences of prolonged developmental times and/or reduction in appendage mobility, so as the effects of these compounds on the pelagic and benthic communities.

Tide-related biological rhythm in the oxygen consumption rate of ghost shrimp (Neotrypaea uncinata).

The effects of tidal height (high and low), acclimation to laboratory conditions (days in captivity) and oxygen level (hypoxia and normoxia) were evaluated in the oxygen consumption rate (OCR) of the ghost shrimp Neotrypaea uncinata We evaluated the hypothesis that N. uncinata reduces its OCR during low tide and increases it during high tide, regardless of oxygen level or acclimation. Additionally, the existence of an endogenous rhythm in OCR was explored, and we examined whether it synchronized with tidal, diurnal or semidiurnal cycles. Unexpectedly, high OCRs were observed at low tide, during normoxia, in non-acclimated animals. Results from a second, longer experiment under normoxic conditions suggested the presence of a tide-related metabolic rhythm, a response pattern not yet demonstrated for a burrowing decapod. Although rhythms persisted for only 2 days after capture, their period of 12.8 h closely matched the semidiurnal tidal cycle that ghost shrimp confront inside their burrows.

Thermal biology of the sub-polar-temperate estuarine crab Hemigrapsus crenulatus (Crustacea: Decapoda: Varunidae).

Optimum temperatures can be measured through aerobic scope, preferred temperatures or growth. A complete thermal window, including optimum, transition (Pejus) and critical temperatures (CT), can be described if preferred temperatures and CT are defined. The crustacean Hemigrapsus crenulatus was used as a model species to evaluate the effect of acclimation temperature on: (i) thermal preference and width of thermal window, (ii) respiratory metabolism, and (iii) haemolymph proteins. Dependant on acclimation temperature, preferred temperature was between 11.8°C and 25.2°C while CT was found between a minimum of 2.7°C (CTmin) and a maximum of 35.9°C (CTmax). These data and data from tropical and temperate crustaceans were compared to examine the association between environmental temperature and thermal tolerance. Temperate species have a CTmax limit around 35°C that corresponded with the low CTmax limit of tropical species (34-36°C). Tropical species showed a CTmin limit around 9°C similar to the maximum CTmin of temperate species (5-6°C). The maximum CTmin of deep sea species that occur in cold environments (2.5°C) matched the low CTmin values (3.2°C) of temperate species. Results also indicate that the energy required to activate the enzyme complex (Ei) involved in respiratory metabolism of ectotherms changes along the latitudinal gradient of temperature.

Physiological responses of the ghost shrimp Neotrypaea uncinata (Milne Edwards 1837) (Decapoda: Thalassinidea) to oxygen availability and recovery after severe environmental hypoxia.

Hypoxia is a common and widespread phenomenon in aquatic ecosystems, imposing a significant challenge for the animals that inhabit such waters. In different habitats, however, the characteristics of these hypoxic events may differ, therefore imposing different challenges. We investigated the tolerance of adult ghost shrimp Neotrypaea uncinata (an intertidal mudflat dweller) to different partial pressures of oxygen (pO2), severe hypoxia (2 kPa) and recovery from hypoxia after different exposure times, mimicking the natural tidal cycle (6 h and 12 h). We calculated critical oxygen tension and categorize the adult ghost shrimps as oxyregulators (R value=75.27%). All physiological measurements (metabolic rate, oxyhemocyanin, hemolymph protein and lactate concentrations) were affected by exposure to low partial pressures of oxygen, but most of them recovered (with exception of metabolic rate) control values (21 kPa) after 6h under normoxic conditions. Low metabolic rate, high release of hemolymphatic proteins and anaerobic metabolism are suggested as response mechanisms to overcome hypoxic events during low tide.