Indicators of stress in tilapia subjected to different stunning methods

Abstract

Nile tilapia is one of the main fish species cultivated in the world. However, there are few studies evaluating the effects of stunning methods on the stress of this fish. The aim of this study was to evaluate the effect of electrical stunning (ES), CO₂ narcosis (CN), and iced water (IW) on indicators of stress in tilapia, e.g., muscle adenosine triphosphate (ATP), enzymatic antioxidants (catalase, lactate dehydrogenase and glutathione reductase) and plasma cortisol. The muscle ATP was highest (P<0.05) in fish stunned by CN. However, the cortisol level was higher (P<0.05) in tilapia stunned by IW and CN. The levels of catalase in the white muscles were higher (P<0.05) in fish stunned by ES than in fish stunned by CN and IW. For the red muscles, the highest levels (P<0.05) of catalase were observed in tilapia stunned by ES and IW. Lactate dehydrogenase levels in the white muscles were higher (P<0.05) in fish stunned by ES and lower (P<0.05) in fish stunned by CN. In the red muscles, lactate dehydrogenase levels were higher (P<0.05) in fish stunned by IW in comparison to ES and CN. Therefore, in tilapia stunned by CN, the stress is lesser when compared to that caused by ES or IW and is in accordance with good practices of animal welfare.