Abstract
Dactylogyrideans infect the gills of Colossoma macropomum (tambaqui), causing parasitosis that requires therapeutic intervention. Phytotherapeutics may provide an alternative to chemotherapeutants, which have limited efficacy.This study evaluated the anti-dactylogyridean efficacy of Astrocaryum aculeatum fixed oil on tambaqui, as well as the effects of bath treatments on hematological parameters and gill histopathology. The fixed oil, composed predominantly of palmitic and oleic acids (95.5%), exhibited in vitro efficacy against the dactylogyrideans Anacanthorus spathulatus , Notozothecium janauachensis , and Mymarothecium boegeri , with efficacy depending on the dose. The tegument of these dactylogyrideans exhibited few structural alterations that could account for the observed efficacy. Fish tolerated baths containing 20–160 mg/L of A. aculeatum fixed oil, as no fish died and similar behavioral changes were observed across all concentrations. The highest concentration of A . aculeatum fixed oil (160 mg/L) was then used in 2-h therapeutic baths administered over four consecutive days to tambaqui, alongside one group exposed to culture tank water (negative control) and another exposed to absolute ethyl alcohol (positive control). These bath treatments achieved high efficacy (74.4%) against dactylogyrideans infecting the gills of tambaqui. Treatment with A. aculeatum fixed oil increased plasma protein and glucose levels, as well as mean corpuscular volume, while decreasing mean corpuscular hemoglobin concentration. Fish exposed to ethyl alcohol developed macrocytic hypochromic anemia, and no severe structural alterations of the gills were observed in any of the three groups. Therefore, baths with A. aculeatum fixed oil were effective against dactylogyrideans infecting tambaqui without compromising gill structure, as they induced mild stress in the fish and should therefore be administered with caution.