Tilapia On-Farm Welfare Assessment Protocol for Semi-intensive Production Systems

Abstract

The aim of this study was to develop and test a tilapia on-farm welfare assessment protocol, based on Brazilian semi-intensive production systems. The study included two mains steps: the elaboration of tilapia welfare protocol and its on-field feasibility test. The protocol, including the potential indicators organized into health, environmental, nutritional, and behavioral categories, was tested on three farms. Skin, eyes, gills, jaws, fins, and vertebral spine were individually examined in 139 individual tilapias. Water physicochemical parameters and production system were considered. The overall nutritional status of individuals was assessed through body condition factor, feed conversion ratio, feed crude protein ratio, and feed ingestion behavior. During massive capture, signals of stress, level of crowding, and duration of air exposure were registered. Time required for loss of consciousness was evaluated by clinical reflexes and other behaviors during slaughter. Eye, jaw, and gill scores were different across farms (Kruskal-Wallis test, p = 0.011; 0.015; 0.043, respectively), showing good discrimination power. Critical welfare points were extremely low dissolved oxygen in water, fin and skin lesions, prolonged air exposure during pre-slaughter handling and non-humane slaughter techniques, as decapitation or asphyxia. The protocol presents practical viability and it is an initial step for the development of a tilapia welfare strategy, where the prioritization of critical welfare points, implementation of corrective actions and monitoring of the results is part of a permanent welfare management system.

Welfare in Nile Tilapia Production: Dorsal Fin Erection as a Visual Indicator for Insensibility

“…However, the absence of a DFE alone does not ensure that fish have been totally stunned, and it must be used together with other well-established VSIs to obtain a more accurate assessment of the state of fish sensibility before slaughter in fish farms. The VOR is a clinical reflex that has been well-established to assess the state of fish sensibility [11,18,25]. Usually, the VOR is lost in stage 4 of anesthesia, along with the responses to external stimuli and opercular beats decreasing [25].…”

“…Although immersion into ice water and CO 2 stunning are considered non-humane stunning protocols [12], we used these stunning methods since they are still the most used in Brazil and some European countries [5,14,15]. After the fish were submitted to one of these three stunning methods, we assessed the time for the VOR (Figure 2B,D) to be lost and its return, a clinical reflex and well-established indicator of unconsciousness/insensibility in fish [11,18,25], and the DFE, aiming to test whether this response to a stimulus presented in Nile tilapia (Appendix A) could be used as a visual sensibility indicator (VSI). To test the presence/absence of both VSI, we removed fish from the water using a dip net.…”

“…This current attitude is changing the traditional production model that has been used for years [10]. Therefore, it is necessary to have well-established protocols with clear guidelines that ensure fish welfare in all farming stages, from rearing the fish to slaughtering them [11].…”

“…Regarding self-initiated behavior and responses to stimuli, whether fish are able to detect and react to external events, they retain sufficient brain function to perceive strong and painful external stimulus, such as the slaughter [18]. However, all the behavioral responses used to assess the state of sensibility in fish depend on a painful stimulus, such as a tail pinch, prick or shock on a lip [11,18]. Therefore, behavioral responses that allow us to assess the state of sensibility in fish that do not depend on a painful stimulus must be investigated and incorporated into protocols that have been developed to assess fish insensibility before slaughter [11,18], avoiding any unnecessary pain and suffering in this procedure.…”

“…The Nile tilapia is an African cichlid, which presents DFE behavior in aggressive displays during hierarchical and territorial confrontations [23,24] and when a threat or predation risk is perceived [23]. In addition, the Nile tilapia is the third most-farmed fish species globally [1] and has a welfare assessment protocol for production systems, including the assessment of the state of fish sensibility pre-slaughter using visual indicators [11]. As such, the continuous refinement of welfare protocols is important for a better assessment of the welfare of Nile tilapia during all the production stages.…”