Fish species belonging to the Clupeidae family (such as sardine and herring). The allis shad are among the anadromous species (i.e. which swim up rivers to spawn in the middle part of the rivers). As such, their populations have paid a heavy price to river development (dams without fish pass facilities, extraction of gravel changing the spawning, etc). Their presence is therefore a good indicator of the status of a river development. Two species of allis shad are present (and exploited) in French waters: the allis shad (Alosa Alosa) and twaite shad (Alosa fallax).