Gaston K.A., Jacquemin S.J., Lauer T.E. 2013. The influence of preservation on fish morphology in museum collections based on two species of the genus Lepomis (Actinopterygii: Perciformes: Centrarchidae). Acta Ichthyol. Piscat. 43 (3): 219–227.
The wide availability of specimen-based museum collections allows scientists to address a variety of ecological and systematic hypotheses from a broad timeframe and extensive spatial scale. However, techniques employed to preserve and maintain these collections affect morphology, potentially altering or skewing any morphological comparisons inherent in research study questions. The purpose of this study was to better understand and describe the effects that preservation techniques may have on fish specimens.
Materials and methods.
Bluegill, Lepomis macrochirus Rafinesque, 1819, and green sunfish, Lepomis cyanellus Rafinesque, 1819, were initially preserved for six weeks in a 10% formalin solution and then transferred to 70% ethyl alcohol for 46 additional weeks to determine how the commonly used preservation methods influence morphology. Fish were photographed at 0, 3, 6, 12, 24, 39, and 52 weeks of preservation to assess changes in shape. Standard length and maximum depth were measured on all fish images using Sigma Scan Pro. These measurements were then used to generate aspect ratios (maximum depth vs. standard length) for each fish. Additionally, geometric morphometric techniques (relative warp analysis) using 10 digital landmarks, were also used to evaluate overall morphological change.
During the 52-week period of preservation, fish standard length was reduced, but this dimension shrank proportionally with body depth. This finding was confirmed along the major gradients elicited from relative warp axis scores tested using repeated measures ANOVA. However, with both species, morphological contortions were observed immediately after the fish were placed in formalin and again when this fixative was replaced with ethyl alcohol.
Ultimately, shape stabilized after a period of acclimatization of up to 39 weeks. This stabilization phenomenon provides evidence that long term museum collections do plateau in shape change and may be compared to address a variety of ecological and evolutionary hypotheses.
fixation, geometric morphometrics, bluegill, green sunfish, body shape, formalin, ethyl alcohol