Imazapyr plus imazapic herbicide determines acute toxicity in silver catfish Rhamdia quelen

Imazapyr (IMY) and imazapic (IMI) are imidazolinone herbicides which have been associated in a commercial formulation (Kifix (R)). To date, there are no studies on the toxicity of an IMY + IMI herbicide in fish. This work aimed to assess the acute toxicity (24 and 96 h) of IMY + IMI (0, 0.488 and 4.88 a) towards Rhamdia quelen through hematological, biochemical, immunological, ionoregulatory and enzymatic indexes. Red blood cell count was lower at 4.88 than at 0.488 pg/L (24 and 96 h); mean corpuscular volume was lower than control at both concentrations (24 h) and at 0.488 mu g/L (96 h); lymphocytes declined at 4.88 mu g/L comparing to control (96 h); and monocytes increased at 4.88 a (96 h) in comparison with the respective control and with 4.88 mu g/L at 24 h. Aspartate aminotransferase was higher at 0.488 mu g/L (96 h) than the respective control and the respective concentration at 24 h; uric acid reduced at 4.88 a comparing with 0.488 mu g/L (96 h); and cortisol was lower at 4.88 a compared to 0.488 mu g/L and control (96 h). Herbicide exposure lowered plasma bactericidal activity at both concentrations (24 h) and at 0.488 a (96 h); and plasma complement activity declined at 4.88 mu g/L comparing with 0.488 mu g/L and control (96 h), and was lower at all concentrations at 96 h than at 24 h. Plasma K+ levels were higher at 4.88 than in the remaining groups (24 and 96 h); and Na+ levels decreased at 4.88 a compared to control (96 h). Na+/K-ATPase and 11-ATPase activities in gills were lower at 4.88 a comparing with control (24 h) and with the respective concentration at 96 h; and AChE activity in brain was higher at 0.488 and 4.88 mu g/L than control (24 h) and the respective concentrations at 96 h, while in muscle it was higher at 0.488 and 4.88 a than control (96 h) and the respective concentrations at 24 h. The present findings demonstrate that, despite IMY + IMI targets the animal-absent AHAS enzyme, such formulation displayed an acute toxic effect upon R. quelen homeostasis by impacting on vital functions such as immune defense, metabolism, ionoregulation and neurotransmission. (C) 2016 Elsevier Inc. All rights reserved.