Rainbow trout, a species farmed and consumed worldwide, have long been subjected to a quiet and often invisible suffering. A new study has shed light on the intense distress these fish endure when killed by air asphyxiation, a common method in the industry. The findings, published in Scientific Reports, reveal that trout experience up to 10 minutes of excruciating pain—pain that can stretch up to 25 minutes in certain circumstances. This discovery is prompting calls for reform in fish slaughter methods, urging a shift toward more humane practices.
The Distressing Reality of Air Asphyxiation
When rainbow trout are removed from water, they begin a slow and painful decline. Their gills collapse, their bodies struggle to extract oxygen, and panic sets in as their blood chemistry unravels. This process, known as air asphyxiation, is still widely used in commercial fishing and farming, despite its prolonged and intense nature.
The research team, led by Dr. Wladimir Alonso from the Welfare Footprint Institute, applied the Welfare Footprint Framework (WFF), a new tool designed to measure pain in animals, to quantify the suffering trout endure. Their findings suggest that fish can experience moderate to extreme pain for up to 25 minutes, a far longer period than previously thought.
The team identified distinct phases in the trout’s suffering, ranging from initial panic to the eventual shutdown of brain activity. During these stages, the fish’s vital functions continue to deteriorate, compounding their distress. For an average-sized trout, the pain lasts for about 10 minutes, but under certain conditions, such as fish size or water temperature, the suffering can be much longer.
The study used neurophysiological data, including EEG signals, to measure when the trout lost consciousness, confirming that the experience was neither swift nor painless.
(B) Cumulative Pain table showing time in pain (negative affect) at each intensity (obtained by multiplying the probability of each pain intensity by the duration of each segment, which is then summed across all intensities). Since Segments I-III have identical probabilities, they are analyzed as one time period for Cumulative Pain calculation.
Humane Alternatives: Could Stunning Be the Answer?
The study raises the question: Can we reduce the suffering of fish during slaughter? The researchers evaluated two potential alternatives: electrical stunning and percussive stunning. Electrical stunning, when properly applied, could save between 60 and 1,200 minutes of suffering for every dollar invested. However, its success depends heavily on correct equipment placement, adequate voltage, and operator precision.
The team acknowledged that inconsistent performance of electrical stunning devices in commercial settings undermines its potential benefits. Percussive stunning, a method involving a physical blow to the head, has demonstrated better consistency in laboratory tests. However, scaling this method to commercial operations remains a challenge due to variations in fish size and the need for precise calibration of equipment.
The implications of these findings are significant, as they point to a more humane way of handling fish slaughter. While electrical stunning shows promise, percussive stunning appears to offer a more reliable solution, especially if the industry can overcome the practical hurdles it faces.
The Welfare Footprint Framework: A New Way to Measure Suffering
The Welfare Footprint Framework, which the research team used in this study, is a key tool in evaluating animal welfare. Unlike other models that rely on subjective expert opinions, the WFF quantifies animal pain by measuring the cumulative time spent in different emotional states, such as pain and distress.
This framework allows scientists to break down the pain into time segments, making it easier to compare across species and conditions. According to Dr. Alonso, the WFF’s transparency and ability to incorporate probabilities make it a powerful tool for understanding the complexities of animal suffering, especially in the context of commercial practices like fish slaughter.
In the case of rainbow trout, the WFF provided a detailed picture of the pain the fish experience during air asphyxiation. The research demonstrated that while the pain starts immediately after removal from water, it gradually intensifies, reaching the most severe level before the fish lose consciousness. This new understanding of fish suffering could drive regulatory changes in the fishing and aquaculture industries, leading to better welfare standards for farmed fish.
