But walk through the doors of Opercule’s self-described “urban fish farm,” and the unmistakable smell of fish fills the air. After donning rubber boots and lab coats, visitors are greeted with the constant hum of the plant’s filtration system. Inside the dimly lit warehouse basement, thousands of sleek, speckled Arctic char swim in a dozen or so round pools, their fins smoothly breaking the surface or sending up alarmed splashes as they scurry away from people who approach the tanks.