Effects of stunning methods on pre rigor changes in rainbow trout (Oncorhynchus mykiss) reared at two different temperatures

Anna Concollato,Giulia Secci,Antonella Dalle Zotte,Sheyla Cristina Vargas,Rolf Erik Olsen,Adja Cristina Lira De Medeiros,Giuliana Parisi

doi:10.1080/1828051x.2020.1759465

Abstract

The effects of two stunning methods (carbon monoxide asphyxia, CO, and electroshock, E) on blood plasma parameters, rigor index, fillet pH and shape changes, ATP breakdown and Adenylate Energy Charge (AEC) in muscle immediately post mortem were investigated in rainbow trout (Oncorhynchus mykiss) kept in tanks containing water set at 8 °C or 12 °C. Both the methods here adopted induced a stress-response which, however, was not able to affect the rigor mortis development and fillet pH. The fillets from the E group showed the strongest length contraction and width increase at 48 h post mortem. The CO stunning method exhibited the highest levels of both ATP and AEC in the muscle immediately after death, equal to 2.28 µmol/g and 0.83, respectively, while 1.12 µmol/g and 0.64 values were found in the E group. In addition, we found that the water temperature might interact with the stunning method and minimise the stress response. In the present trial, the most suitable use of the CO stunning method would be coupled with 12 °C of rearing water temperature to better preserve ATP and AEC in muscles. Highlights CO stunning preserves ATP and AEC in trout muscle better than electrical stunning Water temperature might interact with the stunning and minimise the stress response CO stunning is suggested to be coupled with 12 °C of water temperature Electricity should be avoided at 8 °C of water temperature

Highlights

Conditions of anxiety, pain, suffering or fear above all have ethical implications, since the human being is considered to be responsible for the effective respect of the rights and welfare of other living animals, as stated in the declaration of UNESCO (1978)
The effects of two stunning methods on blood plasma parameters, rigor index, fillet pH and shape changes, adenosine 50-triphosphate (ATP) breakdown and Adenylate Energy Charge (AEC) in muscle immediately post mortem were investigated in rainbow trout (Oncorhynchus mykiss) kept in tanks containing water set at 8 C or 12 C
The most suitable use of the carbon monoxide (CO) stunning method would be coupled with 12 C of rearing water temperature to better preserve ATP and AEC in muscles

Summary

Introduction

Conditions of anxiety, pain, suffering or fear above all have ethical implications, since the human being is considered to be responsible for the effective respect of the rights and welfare of other living animals, as stated in the declaration of UNESCO (1978). Operations concerning stunning and slaughtering processes can cause different degrees of stress and disturbances that may affect meat quality (Poli 2009). Percussive, spiking and electrical (E) stunning/ slaughtering methods are listed; whereas, in the second, carbon dioxide (CO2) narcosis, carbon monoxide (CO), asphyxiation in the air, asphyxia in ice/ice slurry, dry salt/ammonia bath and exsanguinations are included. Carbon monoxide is not widely applied in fish, but it has been used in animal euthanasia for long time (Smith 2001). Studies in Atlantic salmon (Bjørlykke et al 2011, 2013), tilapia (Mantilla et al 2008), and the early study of Concollato et al (2019) on rainbow trout (Oncorhynchus mykiss) suggest that CO can be an excellent fish sedative that does not elicit any visible stress response. As previously reviewed by Concollato et al (2015), CO binds with strong affinity to the haem group of haemoglobin (Hb) and myoglobin (Mb) displacing oxygen and producing carboxy-haemoglobin (COHb) and carboxy-

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