Enables glucosylceramidase activity. Acts upstream of or within several processes, including glucosylceramide catabolic process; swimming; and swimming behavior. Predicted to be located in lysosomal membrane. Is expressed in brain; fertilized egg; fin; liver; and oocyte. Used to study Gaucher's disease. Human ortholog(s) of this gene implicated in Gaucher's disease (multiple); Lewy body dementia; Parkinson's disease (multiple); and Parkinsonism. Orthologous to human GBA1 (glucosylceramidase beta 1).