Chapter 3: Fish

Abstract

Despite being a relatively new field of research, many studies on fish welfare in aquaculture have considered the possible negative effects of preslaughter handling. In this Chapter we review the potential negative effects of feed withdrawal, crowding, emersion (removal of the fish from water), transport and different types of stunning and killing on fish welfare. As ectotherms fish require a rather prolonged fasting period before slaughter to empty their digestive tract, with some positive and negative effects depending on the duration. Recent findings are reviewed in terms of maximum fasting durations and the effects of water temperature. Crowding is normally performed using nets and is known to be stressful, especially when prolonged. Recent literature is reviewed in terms of its effects on physiological welfare indicators and the reduction of repeated or cumulative stressors. Emersion is often done by hand or using a crane and is possibly one of the more acute stressors during pre-slaughter handling. The literature is reviewed in terms of its negative effects and duration limits. Transport is not always necessary but can be of long duration and expensive. Loading and unloading procedures appear to be the most stressful while water quality changes become important for longer distances and higher densities. Lastly, regarding stunning and killing, many fish either die by asphyxia in air or in an ice slurry, with negative effects on welfare, but other mechanical methods and electronarcosis are discussed. Studies on the effects of dry stunning are considered as well as in-line in-water stunning, where fish are pumped through a long-electrified tube connected between the tank and the processing line. Other methods used to make fish unconscious are also discussed, such as gas stunning and the use of clove oil.