Eyestalk ablation procedures to minimize pain in the freshwater prawn Macrobrachium americanum

This article proposes an enhanced and less painful procedure to eliminate the flow of hormones from the X organ sinus gland in adult Macrobrachium americanum. Three groups and two controls were analyzed to determine the amount of stress caused by the following: (1) unilateral eyestalk ablation, (2) unilateral eyestalk ablation and covering to allow coagulation, and (3) ligation at the base of the eyestalk. Each group was divided into two subgroups to analyze the effect of treatment with and without Xylocaine. For males and females, the control groups were only manipulated but not ablated. The trauma caused by the treatments in M. americanum was reflected by behaviors related to pain, including tail flicking as a reflex response to allow escape and rubbing the affected area. In addition, we also observed alterations in five behaviors. Four behaviors were directly related to pain and discomfort – non-sheltering, disorientation, recoil and stooping – and the fifth, feeding behavior, was related to the hormonal disorder caused by the extirpation of the X organ sinus gland. The variables that were directly affected by the treatments were bleeding, ligating and hormonal state. The treatment that caused the most significant negative stimulus was ligation. The animals in the ligation group exhibited up to 50% more flicking, 90% more rubbing, 50% more disorientation, and 80% more recoil than the animals in the other subgroups. Ablation without covering to allow coagulation was a moderate significant negative stimulus. Finally, the treatment with the least negative stimulus was the treatment of females using anesthetic and ablation followed by covering to allow coagulation. This subgroup exhibited only 20% more flicking and 20% more rubbing than controls, and only 30% were not sheltered. These prawns also did not show disorientation, recoil or stooping.