Effects of various alternative stunning techniques on welfare indicators and meat quality of Nile tilapia

Abstract

Introduction: Humane slaughter practices are increasingly recognized as essential for improving fish welfare and maintaining product quality in aquaculture systems. In tilapia production, inappropriate stunning and killing methods can induce severe stress responses, leading to compromised welfare, accelerated rigor mortis, and reduced fillet quality. Despite the availability of multiple stunning techniques, comparative evidence linking welfare indicators to postmortem biochemical changes and fillet quality remains limited. This study aimed to evaluate and compare the effects of six commonly used stunning methods on welfare outcomes and flesh quality in Nile tilapia. Materials and methods: A total of 54 Nile tilapia (Oreochromis niloticus) were randomly allocated to six slaughter treatments (n = 9 per group): priest stunning, bolt pistol, ikijime, live freezing, anesthetic overdose, and asphyxiation. Fish welfare was assessed immediately post-stunning using behavioral response (BR) scores and morphological damage (MD) indices. Postmortem physiological and biochemical parameters—including muscle pH, lactate concentration, ATP levels, and rigor mortis index—were analyzed over storage time. Fillet quality was evaluated based on texture, color, proximate composition, and water drip loss. Results: Anesthetic overdose and bolt pistol stunning produced the most favorable welfare and quality outcomes. Both methods resulted in immediate loss of consciousness (BR = 0), minimal morphological damage, and significantly lower muscle lactate concentrations (3.0 ± 0.5 mmol/L) compared with other treatments. Asphyxiation demonstrated the poorest welfare performance, characterized by prolonged behavioral responses (BR = 1), elevated stress biomarkers, rapid rigor mortis onset, and inferior fillet texture, color stability, and storage potential. Live freezing and priest stunning showed relatively acceptable behavioral welfare indicators; however, these methods did not confer advantages in stress reduction or fillet quality parameters. The effectiveness of ikijime varied considerably, largely depending on operator skill and consistency. Discussion: The findings demonstrate a strong association between rapid induction of unconsciousness, reduced physiological stress, and improved fillet quality in tilapia. Anesthetic overdose and bolt pistol stunning consistently outperformed other methods across welfare, biochemical, and quality metrics, highlighting their suitability as humane slaughter techniques. In contrast, asphyxiation remains unacceptable from both welfare and product quality perspectives. Although some traditional methods may appear behaviorally acceptable, their limited benefits on physiological stress and flesh quality reduce their practical value. Overall, these results support the adoption of anesthetic overdose or bolt pistol stunning in commercial tilapia production. Pilot implementation with industry stakeholders is recommended to facilitate ethical compliance, improve product value, and enhance consumer confidence.