Fish don't feel pain though, right?
Short answer: Wrong. Fish have nociceptors and opioid receptors, and they change their behaviour to avoid harm. The evidence they feel pain is solid, the 'fish can't suffer' line is outdated.
Bulletproof framing: fish possess nociceptors and show behavioural and physiological responses consistent with pain. A minority still debate whether this amounts to conscious suffering, but the hardware is not in dispute.
Sneddon, Braithwaite & Gentle (2003)
The objection
“Fish are basically swimming reflexes. No real brain, no pain, they don’t feel a thing on the hook or the deck.”
The answer
The “fish feel nothing” idea is a comfortable holdover that the science has steadily dismantled. In 2003, Lynne Sneddon and colleagues found nociceptors, the specialised nerve endings that detect tissue damage, on the heads of rainbow trout, with properties strikingly similar to those in mammals [1]. The biological hardware for pain is simply there.
The behaviour goes further than the wiring. Fish have opioid receptors, the same system our own bodies use to dampen pain, and administering pain relief changes how an injured fish behaves, which makes no sense if there were nothing to relieve. Their responses run well past bare reflex. Injured fish will rock, rub the affected area, go off their food and pay less attention to things they’d normally fear, and they’ll trade off avoiding a harmful area against other needs. That trade-off is the mark of an experience being weighed rather than a circuit firing [2].
A few scientists still dispute it, arguing we can’t prove fish consciously suffer the way we do. To be straight, that final step is genuinely hard to demonstrate in any animal, including in each other. But it’s a high bar nobody applies to a dog or a pig. The weight of evidence and the precautionary logic both point one way.
So the honest position runs the other way from the objection. Fish have the equipment, they show the behaviour, and we kill them by the trillion on the assumption that they don’t. The evidence says that assumption is a bet we’re losing.