Temporal Effects of Preservation on the Shape and Size of Yellow Perch: Implications for Morphological Analyses

Long-term preservation of fishes often involves fixation in formalin followed by preservation in ethanol. This preservation technique can alter the shape and size of specimens, although the effects are often species and stage specific. In this study, we evaluated the temporal effects of preservation on the shape and body size of adult Yellow Perch (Perca flavescens). We sampled 42 Yellow Perch from three lakes directly connected to Lake Michigan, USA. Upon capture, fish were transported to the laboratory, fixed in formalin, and then preserved in ethanol. Measurements (length, mass, and photograph to analyze shape) were made on fresh fish (i.e., prior to preservation) and 21, 47, and 61 days after being preserved in ethanol. Shape was analyzed using geometric morphometrics. We identified significant changes in shape, and to a lesser degree, size. The most significant shape change occurred in the comparison of pre-preserved versus 21 days, with most of this variation attributed to dorsal bending. Shape changed slightly when comparing 21- versus 47-day but was not detectable between 47- and 61-days post preservation. Total length and to a lesser degree centroid size and mass also differed over time, but total length and centroid size did not follow a similar pattern to shape. Changes in total length and mass were minor (< 1%) and were observed when comparing 47 vs. 61 days and pre-preserved vs. 21 days, respectively. Changes in centroid size were modest (~5%) and were observed paradoxically when comparing 47 vs. 61 days (similar to total length). Although most of the observed differences in the shape and size of adult Yellow Perch were slight, we recommend the conservative approach of only comparing fresh individuals with other fresh individuals and preserved individuals with other individuals preserved for the same amount of time when performing analyses of shape and size.