The morphology of a population ofD. middendorffianacollected during spring and autumn in a fishless pond of the Southern Andes was examined to identify seasonal variations in growth patterns. Body size, tail spine length, width, thickness and biomass were analyzed, and growth was characterized by correlating various morphological dimensions with biomass. A pattern of three growth stages was identified: a juvenile stage characterized by body growth without variation of the tail spine length, a transition stage during which the tail spine experienced a sudden length reduction, and an adult stage with growth patterns similar to the first stage. Specific cyclomorphic growth patterns were found. The dimensions displaying most apparent seasonal differences were tail spine length and body flatness.