1 dialect, rare A North American freshwater mussel, Lasmigona complanata, with rough ridges on the shell.
2 dialect The shovelnose sturgeon, Scaphirhynchus platorynchus, a small freshwater sturgeon of the Missouri and Mississippi river systems. Often attributive, especially with reference to the use of its black roe as caviar.
Late 19th century. From hackle + back.