 The host of freshwater pearl mussel larvae are juvenile fish from the salmonid family, which includes the Atlantic salmon and sea trout.The chances of a larva encountering a suitable fish are very low, and thus nearly all are swept away and die; only a few are inhaled by an Atlantic salmon or sea trout, where they snap shut onto the fish's gills.Attached to the gills of a fish, the glochidia live and grow in this oxygen-rich environment until the following May or June, when they drop off.