Enables (N-acetylneuraminyl)-galactosylglucosylceramide N-acetylgalactosaminyltransferase activity. Involved in ganglioside biosynthetic process. Acts upstream of or within glycosphingolipid metabolic process; lipid storage; and spermatogenesis. Predicted to be located in Golgi membrane and plasma membrane. Is expressed in several structures, including alimentary system; eye; genitourinary system; hemolymphoid system; and nervous system. Human ortholog(s) of this gene implicated in hereditary spastic paraplegia 26. Orthologous to human B4GALNT1 (beta-1,4-N-acetyl-galactosaminyltransferase 1). [provided by Alliance of Genome Resources, Apr 2022]