Efficacy of seed extract of Bixa orellana against monogenean gill parasites and physiological aspects of Colossoma macropomum after bath treatment

This study evaluated the use of therapeutic baths with acetone extract of Bixa orellana seeds on the hematological, biochemical and hormonal parameters and plasma cortisol levels of tambaqui (Colossoma macropomum) parasitized by the monogenean Anacanthorus spathulatus. The extract showed in vitro anthelmintic activity against the parasites, and the fish tolerated the concentrations used in the toxicity test. Based on these results, an in vivo test was performed. A total of 180 juveniles of tambaqui were divided into six treatment groups in triplicate: group 1: basal (fish non-treated and non-parasitized), group 2: exposed to acetone 0.2% and parasitized fish, group 3: control (non-treated and parasitized fish), group 4: parasitized fish treated with 125μg·mL−1 of annatto extract for 2h bath for two consecutive days, group 5: parasitized fish treated with 250μg·mL−1 of annatto extract for 2h bath for two consecutive days, group 6: parasitized fish treated with 125μg·mL−1 of extract for a single bath for 12h. After the last bath, parasitological, hematological, biochemical and hormonal analysis were performed. Annatto extract showed 100% efficacy in all concentrations and times of bath evaluated. Hemoglobin concentration and hematocrit percentage were higher in treated fish with 250μg·mL−1 2h and 125μg·mL−1 12h than that observed in the non-treated fish groups. Glucose was significantly higher in annatto-treated fish and cortisol was significantly higher in acetone group fish compared to other groups. Significant decrease in thrombocyte number was observed in fish after bath with acetone 0.2% compared to basal group, 125μg·mL−1 2h and 125μg·mL−1 12h, as well as decreased number of circulating lymphocytes in fish after bath with acetone 0.2% and 125μg·mL−1 12h in relation to non-treated fish (control). On the other hand, significant increase in WBC count was found in fish treated with 125μg·mL−1 12h in relation to basal and acetone groups. This is the first report on the use of seeds of B. orellana against monogenean parasites of fish. In vitro study model used with gills in Petri dishes and their in situ observation was successful and could be a useful tool for testing substances to treat fish parasites. Annatto extract bath is an efficacious alternative for treating monogeneans. However, more studies must be carried out for better understanding of the mechanism of anthelmintic activity, isolation of bioactive substances and toxicological evaluation before testing in farming conditions.Chemotherapies have been mostly used to treat fish parasites. However, they present consequences to both to environment and human health. Alternatives have been studied to improve the fish health status and control fish parasites. Phytotherapy shows several advantages in controlling parasites and improving the fish health status. This study shows by the first time the use of B. orellana in controlling monogenean parasites and its effects on the hematological, biochemical and hormonal parameters.