A Fish That Lives Two Lives
The hilsa, Tenualosa ilisha, is an anadromous species: it spends most of its adult life in the Bay of Bengal and the coastal sea, then swims hundreds of kilometres upstream into freshwater rivers to spawn. This is the same biological strategy used by salmon, and it makes the hilsa acutely sensitive to everything that happens along the entire length of a river, not just the stretch where it's caught. A dam, a sand bar, a sewage discharge point, an industrial effluent pipe: any of these can interrupt the migration before the fish reaches its breeding ground. The hilsa doesn't get a second chance. If it can't reach the spawning site, it doesn't breed that season.
