Anesthetic and anthelminthic effects of clove basil (Ocimum gratissimum) essential oil for tambaqui (Colossoma macropomum)

• Tambaqui is the main farmed fish in north Brazil, and is frequently infected with monogean parasites.
• The anthelmintic effect of clove basil essential oil was tested to replace the chemical treatment.
• Tambaqui tolerated baths with clove basil essential oil showing different anesthetic stages, and serum ammonia increase.
• Clove basil essential oil shows potential for monogenean control in tropical fish farming besides anesthetics properties.

Expensive imported drugs that are sometimes not available in the market are used to anesthetize and avoid handling stress in farmed tambaquis and to control and prevent parasites, especially monogeneans. Given that the use of these chemicals poses intoxication risks to fish, farm workers, consumers and the environment; the present study evaluated the anthelmintic and anesthetic properties of a natural product, clove basil (Ocimium gratissimum) essential oil (OgEO), in tambaqui farming. The first experiment assessed the anthelmintic effects of tambaqui exposure to OgEO at 0, 5, 10 and 15 mg L− 1 in 15-min immersion baths; the second evaluated fish blood parameters after 15-min baths in 15 and 60 mg L− 1 OgEO; and the final experiment assessed anesthesia induction time using OgEO at 20, 50, 100, 200 and 300 mg L− 1. OgEO showed anthelmintic and anesthetic effects at concentrations of at least 15 mg L− 1. Fish serum ammonia increased after the baths because of both handling and OgEO exposure, but after 24 h it returned to normal levels, which were exhibited by fish that were not subjected to stress conditions. The findings indicate that the essential oil of clove basil is a safe and efficient ingredient to be used in natural anthelmintic and anesthetic products for tropical fish farming.Statement of relevanceEssential oils can anesthetize and treat ectoparasites of farmed fish at minimum stress level.