Short-Term Effects of the Anti-sea Lice Therapeutant Emamectin Benzoate on Clam Worms (Nereis virens).

The polychaete Nereis virens occurs commonly in marine sediments, is widely distributed, and is a popular bait species, as well as a potential replacement for wild-caught fish in commercial fish feed preparations. It is being considered as a potential co-extractive species for culture in integrated multi-trophic aquaculture operations. However, it is not known whether pesticides or drugs used to treat sea lice on farmed salmon, such as emamectin benzoate (EB), would adversely affect cultured or wild worms, because these compounds may persist in the environment. To determine the potential effects of EB to N. virens, bioassays were performed wherein worms were exposed in sand for 30 days to a concentration of 400 µg/kg dw (nominal). While no treatment-related mortality occurred, significant decreases in worm mass and marked behavioral changes (lack of burrowing) were observed in EB-treated sand compared with controls. These lab-based observations suggest a potential hazard to worms at sites where EB treatments have occurred.

Sublethal exposure to azamethiphos causes neurotoxicity, altered energy allocation and high mortality during simulated live transport in American lobster.

In the Bay of Fundy, New Brunswick, sea lice outbreaks in caged salmon are treated with pesticides including Salmosan(®), applied as bath treatments and then released into the surrounding seawater. The effect of chronic exposure to low concentrations of this pesticide on neighboring lobster populations is a concern. Adult male lobsters were exposed to 61 ngL(-1) of azamethiphos (a.i. in Salmosan(®) formulation) continuously for 10 days. In addition to the direct effects of pesticide exposure, effects on the ability to cope with shipping conditions and the persistence of the effects after a 24h depuration period in clean seawater were assessed. Indicators of stress and hypoxia (serum total proteins, hemocyanin and lactate), oxidative damage (protein carbonyls in gills and serum) and altered energy allocation (hepatosomatic and gonadosomatic indices, hepatopancreas lipids) were assessed in addition to neurotoxicity (chlolinesterase activity in muscle). Directly after exposure, azamethiphos-treated lobsters had inhibition of muscle cholinesterase, reduced gonadosomatic index and enhanced hepatosomatic index and hepatopancreas lipid content. All these responses persisted after 24-h depuration, increasing the risk of cumulative impacts with further exposure to chemical or non-chemical stressors. In both control and treated lobsters exposed to simulated shipment conditions, concentrations of protein and lactate in serum, and protein carbonyls in gills increased. However, mortality rate was higher in azamethiphos-treated lobsters (33 ± 14%) than in controls (2.6 ± 4%). Shipment and azamethiphos had cumulative impacts on serum proteins. Both direct effects on neurological function and energy allocation and indirect effect on ability to cope with shipping stress could have significant impacts on lobster population and/or fisheries.

The influence of water temperature on induced liver EROD activity in Atlantic cod (Gadus morhua) exposed to crude oil and oil dispersants.

Juvenile Atlantic cod were exposed to either the water-accommodated fraction (WAF) or the chemically enhanced water-accommodated fraction (CEWAF) of Mediterranean South American (MESA), a medium grade crude oil at three different temperatures. Two concentrations of each mixture were tested, 0.2% and 1.0% (v/v) at 2, 7 and 10°C. Corexit 9500 was the chemical dispersant tested. The liver enzyme ethoxyresorufin-O-deethylase (EROD) was measured during a 72-h exposure. The WAF of oil had significant (P<0.05) effect on enzyme activity compared to controls at only one sampling time: 48 h at 10°C. Exposure of CEWAF of oil resulted in significantly (P<0.05) elevated EROD activity compared to controls. The level of EROD induction was temperature related with higher induction being observed in cod exposed to CEWAF at higher temperatures. Total polycyclic aromatic hydrocarbon (PAH) concentrations in exposure water were significantly higher in chemically dispersed mixtures. While PAH concentrations were lower in the 2°C water compared to 7 or 10°C (8.7 vs 11.9 µg mL(-1)), the level of EROD induction was approximately 9 and 12 times lower at 2°C compared to 7 or 10°C, respectively, suggesting the metabolic rate of the cod plays a role in the enzyme response. These data suggest the risk of negative impacts associated with exposure to chemically dispersed oil may be affected by water temperature and that risk assessment of potential effects of WAF or CEWAF should consider the effects of water temperature on the physiology of the fish as well as the effectiveness of dispersants.

The effect of repeated exposure to azamethiphos on survival and spawning in the American lobster (Homarus americanus).

The azamethiphos formulation Salmosan has been used to control sea lice on Atlantic salmon. To determine the effect of this pesticide on spawning in the American lobster, pre-ovigerous females acclimated to 13 degrees C were given biweekly 1-h exposures to Salmosan at concentrations of 1.25-10 microg/L azamethiphos. In March and April, four exposures to 1.25, 2.5, or 5.0 microg/L had no significant effect on survival or spawning incidence, while three or four exposures to 10 microg/L caused high mortality (43-100%). Spawning incidence in the surviving lobsters in the 10 microg/L groups was significantly reduced in the group given four treatments, but not in the group given three treatments. In December and January, four exposures to 10 microg/L azamethiphos had no significant effect on either survival or spawning incidence. The results demonstrate that repeated 1-h biweekly exposures to azamethiphos can have a negative effect on survival and spawning in female American lobsters. The response to this pesticide appears to be influenced by time of year, as well as concentration and number of exposures.

Relationship between dose of emamectin benzoate and molting response of ovigerous American lobsters (Homarus americanus).

A widely-prescribed treatment to control sea lice on cultured salmon is the administration of feed medicated with SLICE (active ingredient emamectin benzoate (EMB)). High doses of EMB can disrupt the molt cycle of ovigerous American lobsters, causing them to enter proecdysis prematurely and lose their attached eggs when the shell is cast. To determine the dose response to EMB, lobsters were forced to ingest doses that ranged from 0.05 to 0.39 microg g(-1). A significant proportion of lobsters given doses of 0.39 and 0.22 microg g(-1) (37% and 23%, respectively) molted prematurely, almost a year earlier than the control group. All the lobsters in the 0.05 and 0.12 microg g(-1) groups molted at the normal time and the mean time of molt was similar to that of the control group. Thus, the no-observed-effect level (NOEL) and lowest-observed-effect level (LOEL) of EMB on the molt cycle were 0.12 and 0.22 microg EMB g(-1) lobster, respectively. To acquire the LOEL, a 500-g lobster would have to consume 22 g of salmon feed medicated with SLICE at a level of 5 microg EMB g(-1) feed.

Seasonal lethality of the organophosphate pesticide, azamethiphos to female American lobster (Homarus americanus).

The organophosphate pesticide azamethiphos is the active ingredient in Salmosan, a product formerly registered in Canada for the treatment of cultured Atlantic salmon against infestations of the ectoparasite Lepeophtheirus salmonis. The 48-h LC50 of azamethiphos to female American lobsters was determined bimonthly for 2 years to determine whether the sensitivity of lobsters to azamethiphos varied with time of year, molt stage, or reproductive stage. The LC50's ranged from 0.61 to 3.24 microg/L. The lobsters were most sensitive to azamethiphos during the spawning and molting seasons which occur in the summer and early fall when seawater temperatures are highest. Testing of compounds on this species for regulatory purposes should take into account that there may be variations in sensitivity during the molt and reproductive cycles.

The lethality of Salmosan (Azamethiphos) to American lobster (Homarus americanus) larvae, postlarvae, and adults.

The pesticide formulation Salmosan (47.5% w/w azamethiphos) is currently registered for use, in Canada, to treat salmonids for infestations of the copepod parasites, Lepeophtheirus salmonis and Caligus elongatus (sea lice). Determination was made of the acute lethality of this product to the three larval stages, the first postlarval stage, and the adult of the American lobster (Homarus americanus), a species of significant economic importance in Eastern Canada. The 48-h LC50 (as azamethiphos) is 3.57 microg/liter for Stage I, 1.03 microg/liter for Stage II, 2.29 microg/liter for Stage III, 2.12 microg/liter for Stage IV (the first postlarval stage), and 1.39 microg/liter for adults. These concentrations are not significantly different from each other, although the variability in response is greater in the larval stages than in the postlarvae or adults. These data when interpreted in conjunction with known physical oceanographic data and chemical dispersion studies indicate that single anti-louse treatments are unlikely to result in mortality among lobsters in the vicinity of salmon farms. However, the sublethal effects of this product and the effects of repeated exposures have yet to be determined.

Lethality of pyrethrins to larvae and postlarvae of the American lobster (Homarus americanus).

Pesticide formulations containing pyrethrins are being used to treat salmonids for infestations of the copepod parasites Lepeophtherius salmonis and Caligus elongatus (sea lice). The acute lethality of one such formulation to four larval stages of the American lobster (Homarus americanus), a species of significant economic importance in eastern Canada, was determined. The formulation tested contained 0.06% pyrethrins and 0.6% piperonyl butoxide (a synergist). Stage I larvae (48-h LC50 = 4.42 microg/liter) were significantly less sensitive than stage II, III, or IV larvae. Stage II larvae (48-h LC50 = 2.72 microg/liter) were significantly less sensitive than Stage III or IV larvae. Stage III and IV larvae were not significantly different in their response to the pyrethrins formulation (48-h LC50 = 1.39 and 0.73 microg/liter, respectively). Most published studies using lobster larvae have reported that the earliest larval stage was the most sensitive to chemicals. The results described here indicate that the earliest larval stage is the least sensitive to the pyrethrins formulation.