Physiological Changes as a Measure of Crustacean Welfare under Different Standardized Stunning Techniques: Cooling and Electroshock

Stunning of edible crustaceans to reduce sensory perception prior and during slaughter is an important topic in animal welfare. The purpose of this project was to determine how neural circuits were affected during stunning by examining the physiological function of neural circuits. The central nervous system circuit to a cardiac or skeletal muscle response was examined. Three commercially important crustacean species were utilized for stunning by immersion in an ice slurry below 4 °C and by electrocution; both practices are used in the seafood industry. The blue crab (Callinectes sapidus), the red swamp crayfish (Procambarus clarkii), and the whiteleg shrimp (Litopenaeus vannamei) responded differently to stunning by cold and electric shock. Immersion in ice slurry induced sedation within seconds in crayfish and shrimp but not crabs and cardiac function was reduced fastest in shrimp. However, crabs could retain a functional neural circuit over the same time when shrimp and crayfish were nonresponsive. An electroshock of 10 s paralyzed all three species and subsequently decreased heart rate within 1 min and then heart rate increased but resulted in irregularity over time. Further research is needed to study a state of responsiveness by these methods

Effects of Clove Oil (Eugenol) on Proprioceptive Neurons, Heart Rate, and Behavior in Model Crustaceans

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)