Institutions: Department of Biology, University of Kentucky, Lexington, KY, USA; Goethe University Frankfurt am Main, Germany; Swansea University, United Kingdom; Aquaculture Research Center, Kentucky State University; Sea Farms Limited, Redditch, Worcestershire, United Kingdom
Abstract: Clove oil contains eugenol as an active ingredient and is used as a topical anesthetic in mammals to remedy pain and to anesthetize fish and other seafood for short periods; however, the exact mechanism of action of eugenol is not fully understood. We examined use of eugenol as a reversible anesthetic in crustaceans by examining its effect on sensory and motor neurons in the Red Swamp crayfish (Procambarus clarkii), Blue crab (Callinectes sapidus) and Whiteleg shrimp (Litopenaeus vannamei) with electrophysiological recordings. The neurogenic heart rate in the three species was also monitored along with behaviors and responsiveness to sensory stimuli. The activity of the primary proprioceptive neurons was reduced at 200 ppm and ceased at 400 ppm for both crayfish (i.e., muscle receptor organ) and crab (i.e., leg PD organ) preparations when exposed to saline containing eugenol. Flushing out eugenol resulted in recovery in the majority of the preparations within five to ten minutes. Administering eugenol to crayfish and crabs both systemically and through environmental exposure resulted in the animals becoming lethargic. Direct injection into the hemolymph was quicker to decrease reflexes and sensory perception, but heart rate was still maintained. Eugenol at a circulating level of 400 ppm decreased electromyogram activity in the claw muscle of crabs. Surprisingly, this study found no change in heart rate despite administering eugenol into the hemolymph to reach 400 ppm in crabs or crayfish but heart rate in shrimp preparations decreased. Our results demonstrate the feasibility of eugenol as a short-term anesthetic for crustaceans to decrease stress during handling or transportation, considering its effectiveness at decreasing sensory input and the quick recovery of upon removal of eugenol. A neurophysiology course took this project on as an authentic course-based undergraduate research experience (ACURE).