Enables polypeptide N-acetylgalactosaminyltransferase activity. Acts upstream of or within protein O-linked glycosylation. Predicted to be located in membrane. Predicted to be integral component of membrane. Predicted to be active in Golgi apparatus. Is expressed in several structures, including alimentary system; brain; eye; integumental system; and limb. Orthologous to human GALNT10 (polypeptide N-acetylgalactosaminyltransferase 10). [provided by Alliance of Genome Resources, Apr 2022]