Enables mannose-6-phosphate isomerase activity. Acts upstream of or within chondrocyte morphogenesis; chordate embryonic development; and liver development. Predicted to be active in cytosol. Is expressed in several structures, including female organism; margin; nervous system; neural tube; and polster. Used to study congenital disorder of glycosylation type I. Human ortholog(s) of this gene implicated in carbohydrate metabolic disorder and congenital disorder of glycosylation Ib. Orthologous to human MPI (mannose phosphate isomerase).