Abstract
Simple SummaryAquaculture has been the fastest-growing production segment in recent years, and as such, it is necessary to have clear guidelines on how fish are reared, stunned and slaughtered, always taking into account their welfare. By aiming for the stunning stage to be efficient, quick and practical before the fish are finally slaughtered in the fish farming process, we propose to verify and validate dorsal fin erection as a painless visual indicator of sensibility in Nile tilapia, ensuring that animals do not suffer during the stunning and slaughtering processes. Our results have validated the method as an effective indicator to assess the state of fish sensibility, and is simple to be carried out in large-scale production systems. The presence/absence of an erect dorsal fin alone does not totally ensure fish insensibility, and must be used together with other well-established visual sensibility indicators, for a better assessment of the state of fish sensibility, such as fish equilibrium, vestibulo-ocular reflex and opercular beats.In aquaculture, to ensure animal welfare in pre-slaughter and slaughter stages, it is fundamental that fish are insensible. A method for evaluating fish insensibility is based on visual sensibility indicators (VSI) assessment (i.e., self-initiated behavior, responses to stimuli and reflexes). However, many stimuli used to assess fish responses are painful. Therefore, this study verifies whether the presence/absence of a dorsal fin erection (DFE) response can be used as a painless VSI in Nile tilapia (Oreochromis niloticus). Three stunning protocols were applied to fish: benzocaine anesthesia (40 mg/L and 80 mg/L), ice water immersion (0–1, 2–3 and 5–6 °C) and CO2 stunning. After these stunning methods were applied in fish, the time of loss and return of DFE was observed, along with the vestibulo-ocular reflex (VOR). All fish stunned using benzocaine and ice water immersion lose both VSIs, while 95% of fish stunned using CO2 lose these VSIs. In all treatments, DFEs return quicker than VOR. Therefore, DFE can be used as a VSI in Nile tilapia, which is simple for producers to assess and does not require a painful stimulus. However, the DFE alone does not totally ensure fish insensibility and must be used together with other well-established VSIs at fish farms.
Highlights
Aquaculture represents one of the major meat production systems for human consumption [1]
The efficiency of common stunning protocols was verified to induce the loss of a clinical reflex that is well-established to assess the state of fish sensibility, vestibulo-ocular reflex (VOR) [18,25]
Regarding the dorsal fin erection (DFE) loss, similar results were observed, since 100% of fish stunned with benzocaine anesthesia and immersion in ice water lost this behavioral response, and 95% of individuals stunned with CO2 lost the DFE (Table 1, Figure 3B,D,E)
Summary
Aquaculture represents one of the major meat production systems for human consumption [1]. The public is increasingly more aware of the importance of animal welfare and the existence of sentience in fish [6,7,8,9]. This current attitude is changing the traditional production model that has been used for years [10]. In the last stage of production, slaughtering, it is well-established that for good welfare, fish must be stunned before killing, avoiding any pain and suffering [12,13]
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