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

LOZANO, ISMAEL E.; DE LA TORRE, FERNANDO R.; LO NOSTRO, FABIANA

Mar del Plata

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

Sociedad de Toxicología y Química Ambiental

Ivermectin (IVM) is one of the most widely used antiparasitics worldwide. It is a potent and effective drug for the treatment and prevention of internal and external parasite infections of both livestock and humans. IVM is excreted unchanged (≈90%) in manure of treated animals. Thus, residues of IVM may reach aquatic systems, affecting non-target organisms such as fish. In this work, the effect on swimming behavior, hematology, biochemical and oxidative stress biomarkers were evaluated in juveniles of the native freshwater fish Prochilodus lineatus (Characiformes), exposed to two environmental concentrations of ivermectin (IVM) (0.5 and 1.5 μg/L) for 15 or 30 days. Behavioral responses assessed included water column use, routine swimming, total distance travelled, total activity time and maximum swimming speed, achieved during the escape response. Biochemical/oxidative stress responses assessed included brain acetylcholinesterase, catalase and glutathione S-transferase activities and lipid oxidative damage. Hematological biomarker analysis included blood glucose levels, hematocrit, hemoglobin concentration, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and mean corpuscular volume. After 15 days exposure, the lowest IVM concentration caused a significant decrease in GST activity and a maximum swimming speed during the escape response. Multivariate analysis with biochemical/stress and behavioral data revealed overall effects of both IVM treatments. On the opposite, after 30 days exposure no changes were observed in any of the biomarkers analyzed. Moreover, multivariate analysis did not show overall effects of IVM for any group of biomarkers in this long-term exposure. Since there are no detectable alterations in biomarkers response after 30 days of exposure to IVM, the observed effects after 15 days of exposure seem to be transient, although the exact length of the transient period is unknown. We assume that fish were under metabolic stress during the first 15 days, but after 30 days, a biochemical readjustment occurred. As life cycle involves extensive migrations, larval drift and temporal settlement in nursery areas, 15 days of exposure seem to be a more realistic environmental scenario for the juvenile stage of P. lineatus. To evaluate the predictive value of these short-term effects of exposure to IVM at population level, other biomarkers are needed.