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Delhi's sewage has made the Yamuna, once home to millions of fish, one of the world's most polluted rivers. (Hashim Badani)
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.
[Read: How much pain should animals endure for science?]
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.
