Short vs. long-term exposure to ivermectin in the sábalo Prochilodus lineatus: the transient nature of early responses in a migratory fish

LOZANO, ISMAEL; DE LA TORRE, F.R.; LO NOSTRO, F

Buenos Aires

Congreso; VIII Congreso Argentino de la Sociedad de Toxicología y Química Ambiental SETAC; 2022

Ivermectin (IVM) is one of the most widely used antiparasitics worldwide. It is a potent andeffective drug for the treatment and prevention of internal and external parasite infections ofboth livestock and humans. IVM is excreted unchanged (≈90%) in manure of treatedanimals. Thus, residues of IVM may reach aquatic systems, affecting non-target organismssuch as fish. In this work, the effect on swimming behavior, hematology, biochemical andoxidative stress biomarkers were evaluated in juveniles of the native freshwater fishProchilodus lineatus (Characiformes), exposed to two environmental concentrations ofivermectin (IVM) (0.5 and 1.5 µg/L) for 15 or 30 days. Behavioral responses assessedincluded water column use, routine swimming, total distance travelled, total activity time andmaximum swimming speed, achieved during the escape response. Biochemical/oxidativestress responses assessed included brain acetylcholinesterase, catalase and glutathione Stransferase activities and lipid oxidative damage. Hematological biomarker analysis includedblood glucose levels, hematocrit, hemoglobin concentration, mean corpuscular hemoglobin,mean corpuscular hemoglobin concentration, and mean corpuscular volume. After 15 daysexposure, the lowest IVM concentration caused a significant decrease in GST activity and amaximum swimming speed during the escape response. Multivariate analysis withbiochemical/stress and behavioral data revealed overall effects of both IVM treatments. Onthe opposite, after 30 days exposure no changes were observed in any of the biomarkersanalyzed. Moreover, multivariate analysis did not show overall effects of IVM for any groupof biomarkers in this long-term exposure. Since there are no detectable alterations inbiomarkers response after 30 days of exposure to IVM, the observed effects after 15 daysof exposure seem to be transient, although the exact length of the transient period isunknown. We assume that fish were under metabolic stress during the first 15 days, butafter 30 days, a biochemical readjustment occurred. As life cycle involves extensivemigrations, larval drift and temporal settlement in nursery areas, 15 days of exposure seemto be a more realistic environmental scenario for the juvenile stage of P. lineatus. Toevaluate the predictive value of these short-term effects of exposure to IVM at populationlevel, other biomarkers are needed