Efficacy, toxicity and histopathological analysis of Astrocaryum aculeatum oil solid lipid nanoparticles on Colossoma macropomum infected by parasitic dactylogyrideans.

This study investigated the efficacy of Astrocaryum aculeatum fixed oil solid lipid nanoparticles (SLNs) on dactylogyridean parasites of Colossoma macropomum gills and effects on hematology and gill histology. The main fatty acid component of A. aculeatum oil was oleic acid (68.0%). Among the concentrations of A. aculeatum fixed oil SLNs tested (250-1000 mg/L), the fish tolerated only 250 mg/L, which was the concentration used in the consecutive five baths of 1 h per day. Two control groups were also used: one with myristic acid + Tween 80 and another with only water from the cultivation tank. The baths have no efficacy against Anacanthorus spathulatus, Notozothecium janauachensis, and Mymarothecium boegeri from C. macropomum gills. Detachment of the gill lamellar epithelium, lamellar epithelial hyperplasia, lamellar hyperplasia with fusion, and aneurysm were damages caused by parasites and not by the treatments. Total number of lymphocytes decreased in the fish exposed to baths with 250 mg/L of A. aculeatum fixed oil SLNs, while other blood parameters were not affected. Although the treatments with A. aculeatum fixed oil SLNs were not effective against parasitic dactylogyrideans as expected, they were not toxic for C. macropomum, because they did not provoke alterations in gills and in physiology.