What Is It Like to Be a Fish? The Surprising Debate Over Fish Pain and Consciousness

What might it feel like to be a fish — to glide through water, extract oxygen from a medium unlike the air we breathe, and navigate a sensory world so different from our own?

For centuries, Western thought dismissed sea creatures as simple, dim, or unconscious. Aristotle placed fishes low on his scala natura, and Plato once associated them with "the lowest depths of ignorance." That cultural bias has made it easy to overlook the real complexity of fish lives and the staggering numbers in which humans use them.

The modern puzzle: can fish feel pain?

In recent decades, science has revealed surprising cognitive and social capacities in many fish species: long-term memories, complex social relationships, tool use in some cases, and sophisticated navigation. Yet a basic question remains contested: can fish experience pain?

Pain is a subjective experience that science cannot directly probe. Still, since the late 1990s and especially in the early 2000s, experimental work by researchers such as Lynne Sneddon, the late Victoria Braithwaite, and Michael Gentle changed the conversation by showing that fish possess nociceptors — neurons that detect damaging or noxious stimuli and send signals to the central nervous system. Nociceptors are necessary for pain but not sufficient: conscious perception requires additional neural processing.

Behavioral and physiological evidence

Researchers designed experiments to test whether fish responses to noxious stimuli go beyond reflexes. Across multiple studies, goldfish and trout prodded with needles exhibited more than immediate withdrawal; some showed brain activity in areas associated with higher processing. Rainbow trout injected with acetic acid or bee venom displayed elevated respiration, reduced appetite, rocking motions, and rubbing at affected areas against tank walls or gravel — behaviors that scientists liken to humans attending to localized pain.

Other findings include associative learning: goldfish avoided areas of a tank where they received electric shocks, sometimes foregoing food to avoid the painful zone. In some experiments, injured fish altered social interactions and typical fear responses, consistent with attention being directed toward the injury.

Why debate persists

Two deep intellectual strands help explain why the question endures. Darwin and many naturalists assumed animal feeling as a given — animal emotions and suffering are continuous with our own. In contrast, the Cartesian tradition, stemming from René Descartes, treated animals as automata: complex machines lacking subjective experience. Modern science, which privileges observable and independently verifiable data, inherits aspects of that split and struggles to settle questions about private experience.

A minority of scientists argue that fish lack certain brain structures, such as the mammalian neocortex, that they consider necessary for conscious pain. Most experts reject the idea that a mammal-like cortex is the only pathway to sentience: birds lack a neocortex yet show clear indicators of complex cognition, and in humans pain is processed across distributed neural systems.

Methodological critiques and standards of proof

Behavioral biologist Georgia Mason and co-author J. Michelle Lavery have urged higher evidentiary standards. They note that many behaviors taken as evidence of pain — licking, rubbing, altered behavior — can appear in decerebrate animals or animals with disrupted forebrain function, which are used as non-conscious comparators. If non-conscious animals can show similar responses, critics argue, then existing tests may not conclusively demonstrate conscious pain.

Mason does not deny the possibility of fish sentience; instead, she calls for more rigorous experiments to close the inferential gap. Importantly, she also advocates a precautionary principle: until stronger evidence exists, it is reasonable to treat fish as though they might suffer.

A broader ethical perspective

Some scholars suggest that focusing narrowly on “Do fish feel pain?” may be the wrong question. Fish are immensely diverse — there are as many species of fish as land vertebrates — and their sensory worlds and neural architectures vary. Rather than ask whether a single light is on or off inside a fish's mind, it may be more productive to ask: What do different species want? What motivates them? What kinds of environments and experiences matter to them?

Cleaner wrasse, for example, have passed mirror-recognition tests; guppies form social preferences; some species show play-like behaviors and complex courtship displays. Such findings expand the possibilities for what fish might feel, think, and value.

Practical consequences

The stakes of this debate are real. Humans kill and farm hundreds of billions of fish annually. How we interpret scientific evidence about fish sentience shapes welfare policies, fishing practices, and public attitudes. Some industry voices have historically leveraged scientific uncertainty to resist welfare regulations, while many animal-welfare researchers argue for reforms based on the best available evidence combined with precaution.

Conclusion: uncertainty, responsibility, and empathy

We may never fully know what it is like to be a fish. That uncertainty can feel melancholy but also invites humility and ethical imagination. If consciousness resists final empirical proof, then part of our response must be a judgment: whom to treat as capable of suffering and deserving of moral consideration. Many researchers recommend a precautionary approach and a shift toward studying fishes' wants and needs in ecologically realistic contexts — an approach that can improve welfare while deepening public empathy for lives that are, in important ways, alien to us.

"Rather than asking whether fish have a light on or off in their minds, we should ask what they want and need," says Becca Franks.

Understanding fish is not only a scientific challenge but an ethical opportunity: to recognize and respond to the rich, varied ways life experiences the world.