Fish have many more kinds of sensors than bacteria do. Their sensors flare when the water temperature spikes, when they come into contact with corrosive chemicals, when a hook rips through their scales and into their flesh. In the lab, when trout lips are injected with acid, the fish do not merely respond at the site. They rock their entire bodies back and forth, hyperventilating, rubbing their mouths against their tanks’ sides or gravel bottoms. These behaviors cease when the fish are given morphine.

Such actions call the ethics of the research itself into question. But the experiences of lab fish are nothing compared with those endured by the trillions of aquatic animals that humans yank, unceremoniously, out of oceans and rivers and lakes every year. Some fish are still alive, hours later, when they’re shoveled into the sickly lit, refrigerated intake tubes of the global seafood supply chain.

Fish pain is something different from our own pain. In the elaborate mirrored hall that is human consciousness, pain takes on existential dimensions. Because we know that death looms, and grieve for the loss of richly imagined futures, it’s tempting to imagine that our pain is the most profound of all suffering. But we would do well to remember that our perspective can make our pain easier to bear, if only by giving it an expiration date. When we pull a less cognitively blessed fish up from the pressured depths too quickly, and barometric trauma fills its bloodstream with tissue-burning acid, its on-deck thrashing might be a silent scream, born of the fish’s belief that it has entered a permanent state of extreme suffering.