Enables glycogen (starch) synthase activity. Acts upstream of or within glycogen biosynthetic process and heart development. Located in cytoplasm and inclusion body. Is expressed in several structures, including alimentary system; brain; genitourinary system; respiratory system; and sensory organ. Human ortholog(s) of this gene implicated in cardiovascular system disease. Orthologous to human GYS1 (glycogen synthase 1). [provided by Alliance of Genome Resources, Apr 2022]