Biological effects of the anti-parasitic chemotherapeutant emamectin benzoate on a non-target crustacean, the spot prawn (Pandalus platyceros Brandt, 1851) under laboratory conditions

Effects of aquaculture effluents on the slender sea pen Virgularia mirabilis

This study aims to assess in situ the impact of effluents originating from an Atlantic salmon (Salmo salar) farm on a nearby slender sea pen (Virgularia mirabilis) field. We evidenced (1) the presence and persistence of emamectin residues (i.e. a common chemotherapeutants used for treating ectoparasites in salmons) in V. mirabilis tissue 56 days after treatment and (2) lethal and sublethal responses of V. mirabilis to effluents discharged by the salmon farm. Particularly, sea pens near the fish farm exhibited significant overproduction of mucus, contraction of polyps' tentacles, and disappearance of associated fauna. Furthermore, sea pens located directly underneath the farm showed substantial tissue necrosis and, in the most severe case, complete tissue loss and mortality. Our results suggest that lethal damages on sea pens occur directly below the farm, and that sublethal effects are visible up to 500 m from the farm. However, the presence of V. mirabilis below the studied farm, which has been active for more than twenty years, suggests that V. mirabilis population possesses the capacity to recover from the impacts of the farm, thereby preventing the complete disappearance from the area. In this context, it would be particularly interesting to run a temporal survey following the health state of V. mirabilis during an entire production cycle to have a more precise overview of fish farm impacts on this species, including during and after the post-production fallowing period.

Effects of the sea lice chemotherapeutant, emamectin benzoate, on metabolism and behaviour of the sea-pen Pennatula phosphorea

Chemotherapeutants used to control infestations by sea lice can be released into the marine environment surrounding aquaculture farms. Among these therapeutic agents, emamectin benzoate is extensively utilized even though its impact on non-target taxa has not been thoroughly examined. In this context, we explored the effects of emamectin benzoate on a common Norwegian habitat-forming species: the phosphorescent sea-pen Pennatula phosphorea. Specifically, we examined P. phosphorea metabolic and responses before, during and after exposure to emamectin benzoate. Results indicate that an 8-day emamectin benzoate exposure (0.8 mg/L) did not induce P. phosphorea mortality or significant behavioural or metabolic modifications. However, we highlighted the presence and persistence of emamectin benzoate in exposed P. phosphorea tissue. These results indicate that emamectin benzoate is unlikely to adversely impact P. phosphorea populations in the environment. However, persistence of emamectin benzoate in tissue constitutes a potential for bioaccumulation with repeated treatments and should be examined in further studies.

A review on the ecotoxicity of macrocyclic lactones and benzimidazoles on aquatic organisms

Despite its wide production and several applications, veterinary antiparasitics from macrocyclic lactones and benzimidazole classes have not received much scientific attention concerning their environmental risks. Thus, we aimed to provide insights into the state of the environmental research on macrocyclic lactone and benzimidazole parasiticides, emphasizing their toxicity to non-target aquatic organisms. We searched for relevant information on these pharmaceutical classes on PubMed and Web of Science. Our search yielded a total of 45 research articles. Most articles corresponded to toxicity testing (n = 29), followed by environmental fate (n = 14) and other issues (n = 2) of selected parasiticides. Macrocyclic lactones were the most studied chemical group (65% of studies). Studies were conducted mainly with invertebrate taxa (70%), with crustaceans being the most predominant group (n = 27; 51%). Daphnia magna was the most used species (n = 8; 15%). Besides, it also proved to be the most sensitive organism, yielding the lowest toxicity measure (EC₅₀ 0.25 μg/L for decreased mobility after 48 h-abamectin exposure) reported. Moreover, most studies were performed in laboratory settings, tracking a limited number of endpoints (acute mortality, immobility, and community disturbance). We posit that macrocyclic lactones and benzimidazoles warrant coordinated action to understand their environmental risks.

Negative effects of the sea lice therapeutant emamectin benzoate at low concentrations on benthic communities around Scottish fish farms

Emamectin benzoate is used as an in-feed treatment for the control of sea lice parasites in all of the main farmed Atlantic salmon (Salmo salar) facilities worldwide (Norway, Chile, Scotland and Canada). Investigations into its effect on non-target benthic fauna resulting from its excretion from farmed fish and uneaten feed have been limited. This paper presents the findings from a study that intended to assess the impact of emamectin benzoate on benthic fauna using a new low detection method for emamectin benzoate. Eight fish farms in the Shetland Isles, Scotland were surveyed, with sediment sampled along transects radiating from the farms analysed for benthic ecology, sediment chemistry and sediment veterinary medicine residues (analysed for emamectin benzoate and teflubenzuron). Canonical Correspondence Analysis (CCA) and Generalised Linear Mixed Modelling (GLMM) were used to assess which environmental parameters observed during the survey had the biggest effect on benthic community composition and abundance, and more specifically crustacean abundance and richness. Emamectin benzoate was found in 97% of samples, demonstrating widespread dispersion in the sediments sampled. The CCA showed that species composition was predominantly ordinated along a gradient of particle size, with a secondary axis dominated by a change in emamectin benzoate and organic carbon enrichment. Peaks in abundance of crustacean species were predicted to be organised along a gradient of emamectin benzoate concentration. The GLMM corroborated this by showing that emamectin benzoate had the strongest negative effect on total crustacean abundance and species richness, though there was some degree of collinearity with organic carbon, that had a smaller effect. Overall, this study shows that, following its use as an in-feed treatment for sea lice, emamectin benzoate residues are more widely distributed in the benthic environment than previously thought, and have a statistically significant effect on benthic ecology at the concentrations observed in this study.

The effects of emamectin benzoate or ivermectin spiked sediment on juvenile American lobsters (Homarus americanus)

This study examined the effects of a range of ½-log concentrations of emamectin benzoate (commercially applied as SLICE^®) and ivermectin (commercially applied as IVOMEC^®) on juvenile American lobster, Homarus americanus. Phase I of the research assessed acute (up to 4 days) and chronic (30-day) toxicity of sediment dosed with the active ingredients emamectin benzoate (EMB) formulated as SLICE^® or ivermectin (IVM) formulated as IVOMEC^® at various nominal concentrations (EMB: 15, 48, 150, 475 and 1500 ng g^-1 wet sediment; IVM: 3, 9.5, 30, 95 and 300 ng g^-1 wet sediment) on juvenile Atlantic lobster (stages IV). Phase II evaluated sublethal effects (e.g., growth, moulting success) of all lobster surviving past the 30 day exposure period, over an additional 41 days. Chemical analysis of EMB and IVM in sediment samples from the exposure tanks revealed a strong linear association (R² values 0.99 and 0.98 for EMB and IVM, respectively) between nominal dose and measured concentration of compound. EMB exposure concentrations at very high levels (≥ 343.3 ng g^-1) were acutely toxic to juvenile lobster such that 100% of lobsters had died after 13 days of exposure. The maximum cumulative mortality of lobsters exposed to the highest concentrations of EMB and IVM was 100% after 10 days and 25 days, respectively. The 10-day LC₅₀ estimates (± 95% CI) for EMB and IVM were 250.23 ± 90.4 and 212.14 ± 202.64 ng g^-1, respectively. Using abnormal behaviour as an indicator, the 15-day EC₅₀ estimates (± 95% CI) for EMB and IVM were 96.19 ± 51.42 and 15.82 ± 6.93 ng g^-1, respectively. The NOEC (no observed effect concentration) for abnormal behaviour was 0.0 ng g^-1 for each product and the LOEC (lowest observed effect concentration) was 8.8 and > 3.0 ng g^-1 for EMB and IVM, respectively. Observations on sublethal effects included delayed moulting to stage VI and reduced growth at higher exposure concentrations for both therapeutants. Using failure to moult to stage V or VI as an indicator, the 15-day EC₅₀ estimates (± 95% CI) for EMB and IVM were 32.72 ± 18.26 and 14.00 ± 12.43 ng g^-1, respectively. The NOEC for failure to moult to stage V only was 343.3 and 14.7 ng g^-1 for EMB and IVM, respectively. Whereas, the LOEC was 1066.7 and > 61.0 ng g^-1 for EMB and IVM, respectively. The concentrations of EMB and IVM tested in the present study were acutely toxic to juvenile lobster exposed to the highest dosages (343.3 and 1066.7 ng EMB g^-1 and 61.0 and 300.0 ng IVM g^-1). There was significant evidence of chronic toxicity, longer exposure increased mortality with LT₅₀ values decreasing with increasing test material concentration.

Host–parasite transcriptomics during immunostimulant-enhanced rejection of salmon lice (Lepeophtheirus salmonis) by Atlantic salmon (Salmo salar)

Salmon lice ( Lepeophtheirus salmonis) are important ectoparasites of wild and farmed salmonids and cause major losses to the salmon farming industry throughout the Northern Hemisphere. With the emergence of resistance to several commonly used parasiticides, novel control strategies and integration of multiple treatment options are needed, including host immunostimulation. Here, we investigate the effects of a functional feed containing a peptidoglycan and nucleotide formulation on L. salmonis infection of Atlantic salmon ( Salmo salar) by characterizing lice infection levels, the expression of several host immune genes, and the parasite transcriptomic response to the immunostimulated host. Although initial infection intensities were low, the low dose (LD) immunostimulant diet reduced the total lice burden by 50% relative to controls. Immunostimulant fed hosts up-regulated interleukin-1β in the skin and spleen. This gene has been implicated in successful responses of several salmonid species to salmon lice but is typically not observed in Atlantic salmon, suggesting a favorable influence on the immune response. Lice infecting LD immunostimulated salmon overexpressed genes putatively involved in parasite immunity, including carboxylesterases, and underexpressed genes putatively involved in feeding (e.g., proteases). These lice response genes further improve the characterization of the transcriptome of the non-model parasite by identifying genes potentially involved in evading host immunity.

Whole-Organism Transcriptomic Analysis Provides Mechanistic Insight into the Acute Toxicity of Emamectin Benzoate in Daphnia magna

Emamectin benzoate (EMB) is an antisea lice chemical widely used in the aquaculture that may also unintentionally affect nontarget crustaceans in the environment. Although the adverse effects of this compound are well documented in various species, the full modes of action (MoAs) are still not well characterized. The current study was therefore conducted to characterize the MoAs of EMB and link perturbations of key toxicological pathways to adverse effects in the model freshwater crustacean Daphnia magna. Effects on molting and survival were determined after 48 h exposure to EMB, whereas global transcriptional changes and the ecdysone receptor (EcR) binding potency was determined to characterize the MoA. The results showed that the molting frequency and survival of D. magna decreased in a concentration-dependent manner, and the observed changes could not be attributed to direct interactions with the EcR. Major MoAs such as activation of glutamate-gated chloride channels and gamma-aminobutyric acid signaling, disruption of neuroendocrine regulation of molting, perturbation of energy homeostasis, suppression of DNA repair and induction of programmed cell death were observed by transcriptional analysis and successfully linked to the adverse effects. This study has demonstrated that acute exposure to intermediate and high pM levels of EMB may pose hazards to nontarget crustaceans in the aquatic environment.

Transcriptomic responses to emamectin benzoate in Pacific and Atlantic Canada salmon lice Lepeophtheirus salmonis with differing levels of drug resistance

Salmon lice Lepeophtheirus salmonis are an ecologically and economically important parasite of wild and farmed salmon. In Scotland, Norway, and Eastern Canada, L. salmonis have developed resistance to emamectin benzoate (EMB), one of the few parasiticides available for salmon lice. Drug resistance mechanisms can be complex, potentially differing among populations and involving multiple genes with additive effects (i.e., polygenic resistance). Indicators of resistance development may enable early detection and countermeasures to avoid the spread of resistance. Here, we collect sensitive Pacific L. salmonis and sensitive and resistant Atlantic L. salmonis from salmon farms, propagate in laboratory (F1), expose to EMB in bioassays, and evaluate either baseline (Atlantic only) or induced transcriptomic differences between populations. In all populations, induced responses were minor and a cellular stress response was not identified. Pacific lice did not upregulate any genes in response to EMB, but downregulated degradative enzymes and transport proteins at 50 ppb EMB. Baseline differences between sensitive and now resistant Atlantic lice were much greater than responses to exposures. All resistant lice overexpressed degradative enzymes, and resistant males, the most resistant group, overexpressed collagenases to the greatest extent. These results indicate an accumulation of baseline expression differences related to resistance.

Modeling parasite dynamics on farmed salmon for precautionary conservation management of wild salmon

Conservation management of wild fish may include fish health management in sympatric populations of domesticated fish in aquaculture. We developed a mathematical model for the population dynamics of parasitic sea lice (Lepeophtheirus salmonis) on domesticated populations of Atlantic salmon (Salmo salar) in the Broughton Archipelago region of British Columbia. The model was fit to a seven-year dataset of monthly sea louse counts on farms in the area to estimate population growth rates in relation to abiotic factors (temperature and salinity), local host density (measured as cohort surface area), and the use of a parasiticide, emamectin benzoate, on farms. We then used the model to evaluate management scenarios in relation to policy guidelines that seek to keep motile louse abundance below an average three per farmed salmon during the March–June juvenile wild Pacific salmon (Oncorhynchus spp.) migration. Abiotic factors mediated the duration of effectiveness of parasiticide treatments, and results suggest treatment of farmed salmon conducted in January or early February minimized average louse abundance per farmed salmon during the juvenile wild salmon migration. Adapting the management of parasites on farmed salmon according to migrations of wild salmon may therefore provide a precautionary approach to conserving wild salmon populations in salmon farming regions.