Enables ammonium transmembrane transporter activity. Involved in ammonium transmembrane transport and regulation of pH. Located in apical plasma membrane. Is expressed in medulla oblongata basal plate ventricular layer; renal calyx; and spinal cord ventricular layer. Orthologous to human RHCG (Rh family C glycoprotein). [provided by Alliance of Genome Resources, Apr 2022]