How do you know whether a fish is stressed? It sounds like a question for a biologist, but for Saif Khawaja it's an entire business model. His company Shinkei, backed by the well-known venture fund Founders Fund, is building a fridge-sized robot that kills fish - humanely, they claim, and more profitably.

The machine is called Poseidon and is mounted on fishing boats. Using computer vision it scans every catch, recognises the species and locates the brain, then spikes it so the fish dies at once, before it can convulse or suffocate. It sounds brutal, but the alternative is a slower death of anywhere from a few minutes to an hour, which floods the fish with stress hormones and lactic acid - spoiling the taste and shortening the shelf life. It's an automated version of ike jime, a centuries-old Japanese technique that fishers have long performed by hand on the dock.

The idea came when Khawaja read an essay at university titled "If Fish Could Scream" - whose point is that fish have no vocal cords, so their suffering is invisible. But Shinkei is long past being just a killing machine. The company now describes itself as a vertically integrated processor: it gives fishers free Poseidon machines, then pays them a higher-than-market price, but takes the whole catch for itself. The fish ends up in a 1,500-square-metre plant in Tacoma and is sold under the brand Seremoni, marketed as fish of "ceremonial quality".

The proof is for now on the menu of Erewhon, the pricey Californian grocery chain beloved by influencers. Khawaja claims he already supplies restaurants with a combined 50 Michelin stars, and even - something that supposedly never happened before - Japan importing American catch onto its markets, which have historically deemed American fish inferior to their own. But whether the buyer will pay extra for "humanely killed" fish, as they already pay for humanely raised meat, remains an open question. Khawaja himself says the real argument isn't ethics but quality: a shelf life of 12 to 14 days instead of 5 to 7.

Behind the whole story sits a bigger game around the supply chain. A large share of fish caught in American waters is frozen and shipped abroad, often to China, for the manual work of cleaning and filleting, then returned. Reports link that Chinese sector to forced labour. Shinkei and Founders Fund's bet is that the whole chain - catch, kill, processing and distribution - can come back home and be profitable enough to beat that cheap foreign labour. Partner Delian Asparouhov put it bluntly: almost no one in the world wants to spend their life building robots that kill fish. Sometimes that's exactly where, in the unwanted, the story hides.