Dr. James Rose (University of Wyoming) argues (2003) that fish do not have the necessary neurological hardware to process pain (or suffer, as we understand the word). Rose maintains that true pain is a psychological experience separate from the initial reaction to an injurious (nociceptive) stimulus. Nociception refers to the detection of actual (or potential) tissue damage by the nervous system. Rose grants that fish have nociceptors (sensory receptors), but mere detection is not the same as pain (even amoebas detect and react to dangerous stimuli by moving away from the source). In vertebrates (fish included), an automatic, coordinated response (withdrawal, struggling, locomotion, and perhaps vocalization) is generated by the brainstem and spinal cord.
Fish have less-developed brains than mammals and birds (according to Rose, the simplest brains of all vertebrates). Mammals, especially, have enlarged cerebral hemispheres with a dominant neocortex that functions as control center for sensations, emotions, and pain. It is here that awareness of pain occurs. Because fish lack a neocortex (and frontal lobe regions), Dr. Rose concludes that they don’t “appear to have the neurological capacity to experience the unpleasant psychological aspect of pain.”
Although fish and human brains have a similar general structure, Dr. Rose likens the fish brain to a ’49 Volkswagen (simple and efficient), while ours are more like a modern luxury car with the capacity for many bells and whistles. He notes that if the cerebral hemispheres are destroyed, humans become comatose, while fish appear to behave normally; fish life is dominated by the brainstem, not the cerebral hemispheres.
Rose does allow for other possibilities: “It might be argued that fish have the capacity to generate the psychological experience of pain by a different process than that occurring in the frontal lobes of the human brain, but such an argument is insupportable.” But in acknowledging the release of stress hormones (“it’s important when practicing catch-and-release fishing to observe the usually recommended procedures of landing a fish before it is exhausted and returning it to the water quickly”), he appears to be hedging his bets, saying the hormones “can have undesirable [italics added] health effects on fish.”
Researchers from the Roslin Institute and University of Edinburgh, however, found that fish do indeed feel pain. Bee venom or acetic acid was injected into the lips of trout (the control group received saline). Those injected with the noxious substances demonstrated rocking motions, rubbed their lips on the gravel, and took three times as long to resume normal feeding. The researchers did not view these behaviors as simple reflexes, or as Dr. Lynne Sneddon said, (BBC News, 4/30/03) it “fulfils the criteria for animal pain.”
In another experiment from 2009, a Purdue University researcher (Joseph Garner) attached foil heaters to two groups (morphine and saline) of goldfish. Both groups exhibited a reflexive response to the stimulus, but those given saline would later demonstrate behavioral changes. Garner said: (Purdue website, 4/29/09) “They [saline group] acted with defensive behaviors, indicating wariness, or fear and anxiety.” Because the fish changed their behavior after the adverse event, this indicates cognitive pain (what Rose denies). Garner: “The goldfish that did not get morphine experienced this painful, stressful event. Then two hours later, they turned that pain into fear like we do. To me, it sounds an awful lot like how we experience pain.”
Dr. Victoria Braithwaite (Edinburgh University) concedes that the absence of a neocortex suggests that fish pain is not the same as human pain but still concludes (Fish Pain Perception): “Recent suggestions that fish cannot experience pain or suffering do not appear to be supported by the current research. The evidence I have presented suggests that fish do have the capacity to experience pain and fear, and therefore we need to consider how to minimise their potential suffering.”
Fish do have central nervous systems and similarly constructed (to mammals) brains. Their reactions (wriggling, flopping, hormone-release) would seem to indicate unpleasant feelings (suffering). Their brains may lack certain refinements, but perhaps we do not fully understand their physiology yet (indeed, we still have much to learn about our own neurological functions). If it is at all possible that fish can suffer (and it seems likely that they can), unnecessary human activities involving them (whether catch-and-release or catch-and-mount/eat) should be considered in a moral context.