Therapeutic baths with glyphosate have antiparasitic effects on monogeneans in the gills of Colossoma macropomum (tambaqui)

Abstract This study investigated for the first time the antiparasitic effects of therapeutic baths with glyphosate against monogeneans of Colossoma macropomum (tambaqui), and alterations in the hematology and histopathology caused by the treatments. In the therapeutic baths with 250 mg/L of glyphosate for 2 hours, during 6 consecutive days, the efficacy (98.5%) against monogeneans (Anacanthorus spathulatus, Mymarothecium boegeri, and Notozothecium janauachensis) in the gills of this host was high. Therapeutic baths with this concentration of glyphosate caused increase in plasma glucose and total protein levels, total number of immature leukocytes, and decrease in the total number of eosinophils. Gills of fish exposed to 250 mg/L of glyphosate showed epithelial detachment, hyperplasia, and hypertrophy, resulting in partial fusion and, occasionally, complete fusion of secondary lamellae, lesions with damage ranging from moderate to severe. Although this chemotherapeutant was effective in controlling monogeneans in the gills of tambaqui and caused few physiological changes, grave histopathological changes were observed. Despite this study providing evidence for a novel chemotherapeutant to control and treat infections by monogeneans in tambaqui, the utilization of glyphosate could not be recommended due to the limitations in the tolerance of this host fish and the gill damage caused.