Toxicological assessment of the anti-salmon lice drug diflubenzuron on Atlantic cod Gadus morhua

Abstract

Increasing use of the chitin synthesis inhibitor diflubenzuron against the ectoparasitic salmon louse Lepeophtheirus salmonis in marine aquaculture has raised concerns over its environmental impacts. This study evaluated how diflubenzuron affects Atlantic cod Gadus morhua, a fish species often found near Atlantic salmon Salmo salar farms, focusing on uptake kinetics and hepatic transcriptional responses. Two experiments were conducted, one time-series trial in which the fish were given a daily dose (3 mg kg −1 fish) of diflubenzuron for 14 d followed by a 3 wk depuration period, and one dose−response trial with increasing concentrations (3, 10 and 50 mg kg −1 fish). The highest diflubenzuron concentrations were found in the liver at Day 15. No detectable levels of diflubenzuron were found in liver or muscle 3 wk after the end of the treatment. At the molecular level, small effects of diflubenzuron treatment on gene transcription were observed. In the time-series experiment, the strongest effects were seen at Day 8, with 2 transcripts being upregulated (bclx2 and cpt1a) and 8 transcripts being downregulated (gstp1, gstm1, gstt1, ugt1a, nat2, cat, p53 and slc16a9a). Five transcripts (cyp3a, cpt1a, ptgs2, elovl5 and mapk1) responded significantly to diflubenzuron exposure in the dose−response experiment. This study shows that diflubenzuron can be taken up by Atlantic cod, that it is rapidly cleared from the body and that when present this pharmaceutical causes only small effects on the expression of genes involved in detoxification pathways. Taken together, our data suggest that accumulated diflubenzuron at the levels studied would have a relatively small effect on wild Atlantic cod.

Transcriptional responses to teflubenzuron exposure in European lobster (Homarus gammarus)

“…In other insect species oxidases seem to play a more important role (Ishaaya, 2009), suggesting a role for cytochrome P450 enzymes. In a previous study with Atlantic cod (Gadusmorhua), diflubenzuron exposure induced CYP3A mRNA in the liver (Olsvik et al, 2013), suggesting that the cytochrome P450 system plays an important role in detoxification of benzoylurea pesticides in fish. Similar findings have been reported from murine experiments (Dubois et al, 1996;Sapone et al, 2005), with increased expression of CYP3A protein after diflubenzuron exposure.…”

“…To control the level of infestation, the salmon farming industry uses considerable amounts of antiparasitic drugs either dissolved in water and used for bath treatment or administered orally via the feed. The increasing use of pharmaceutical drugs to control salmon lice has led to concerns about their environmental impacts (Olsvik et al, 2013;Langford et al, 2014;Samuelsen et al, 2014;Samuelsen et al, 2015;Macken et al, 2015).…”

Safety of medical feed additives in the food chain

“…In two studies by Olsvik et al (2008Olsvik et al ( , 2013, the toxicology of the anti-salmon louse drugs diflubenzuron and emamectin benzoate on Atlantic cod (Gadus morhua) and Atlantic salmon (Salmo salar L.), respectively, was assessed. Three freshwater species exhibited similar sensitivities, with NOEC values of 48.7 mg/L (96 h) for rainbow trout (Oncorhynchus mykiss), 87 mg/L (96 h) for bluegill sunfish (Lepomis macrochirus) and 156 mg/L (96 h) for fathead minnow (Pinephales promelas).…”

“…samples of muscle with skin in natural proportions (EMA, 1998;Olsvik et al, 2013). According to the documentation presented during the establishment of this MRL, the main elimination pathway in Atlantic salmon was the parent drug.…”

Molecular characterisation and functional analysis of LsChi2, a chitinase found in the salmon louse (Lepeophtheirus salmonis salmonis, Krøyer 1838)

“…Chitin synthesis inhibitors have been used as pesticides against salmon louse (Burridge et al, 2010;Denholm et al, 2002), but has lead to concerns regarding the effect of these drugs on non-target organisms. Teflubenzeron has been found in polychaetes and crustaceans in areas of aquaculture (Samuelsen et al, 2015), but was not found to be accumulated in Atlantic cod (Olsvik et al, 2013). Further knowledge regarding the molt process in salmon lice and the biological role of salmon lice chitinases can lead to improvement in the specificity of existing pesticides or development of targets for a vaccine.…”