Before the construction of the causeway, the Petitcodiac River was home to many aquatic species. Fish originally included hundreds of thousands of Atlantic tomcod and rainbow smelt, tens of thousands of gaspereau and American shad, thousands of American eel, Atlantic salmon, brook trout, lamprey, and striped bass and hundreds of Atlantic sturgeon. Other fish include the blueback herring, the brown bullhead, the chain pickerel, the smallmouth bass, the white perch, and the white sucker. Marine mammals were uncommon, but normally consisted of pilot whales, Atlantic white-sided dolphins, harbour porpoise, harbour seals, and porbeagles. Freshwater mollusc species included the brook floater, the dwarf wedgemussel, the eastern elliptio, the eastern floater, the eastern pearlshell, and the triangle floater. Many other aquatic organisms are thought to have once entered the watershed due to the low salinity of the water.