The Influence of Preservation on Fish Morphology in Museum Collections Based on Two Species of the Genus <I>Lepomis</I> (Actinopterygii: Perciformes: Centrarchidae)

Abstract

. 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.Background. 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. Results. 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. Conclusion. 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.Keywords: fixation, geometric morphometrics, bluegill, green sunfish, body shape, formalin, ethyl alcohol preservative; however, more recently this method changed given the toxicity of formalin (Morgan 1997) to using formalin for fixation and ethyl alcohol for preservation (Kelsch and Shields 1996, Al-Hassan et al. 2000). Regardless of the technique, the effects of preservation can be species-and size specific (Ehrlich 1974, Hjörleifsson and Klein-MacPhee 1992, Al-Hassan et al. 2000, Cunningham et al. 2000, Jawad 2003, Santos et al. 2009, Lee et al. 2011 or vary with the type of preservation (Cunningham et al. 2000, Jawad 2003, Santos et al. 2009).The most common effect of preservation is shrinkage, potentially altering morphometric configurations (Al-Hassan et al. 2000, Cunningham ...

Some observations on the biology of two rarely seen deep‐sea chimaerids, Chimaera carophila and Hydrolagus homonycteris

“…Commonly used preservation methodology including fixative (formalin) and preservative (ethyl alcohol) have been found to shrink fishes proportionally along multidimensional planes (Gaston et al ., ). Previous studies on the effects of preservation on elasmobranch and teleost body size have found a decrease in total body length from 2% (Francis, ) to nearly 6% (Jones & Geen, ; Jawad, ; Ebert, ; Gaston et al ., ). To address shrinkage, an increase of 4% was added to external measurements of these specimens.…”

Longitudinal study of rat volar fat pad fixation and ethanol storage: implications for the use of fluid‐preserved specimens in morphological studies

“…; Vervust et al. ; Gaston et al ). Here, the relative regional isolation of each pad likely spares them these changes; it is additionally likely that measurements of the volar surface as a whole (for example, the median length of the surface from the carpometacarpal joint to the 3rd metacarpophalageal joint) would indeed exhibit differences before and after preservation.…”

“…; Gaston et al. ). Further, this shrinkage and associated shape changes have been demonstrated by many authors to be predictable and resolvable with appropriate transformation algorithms (Parker, ; Lasenby et al.…”

“…; Gaston et al. ). Moreover, species classified by traits or measurements that experience preservation changes may be erroneously placed when these changes are poorly understood (Worsaae, ; Oliveira et al.…”

Effect of preservation procedures on the body shape of the golden mojarra, Diapterus aureolus (Actinopterygii: Perciformes: Gerreidae), and its repercussions in a taxonomic study

“…Changes have mainly been based on length or proportion measurements (Leslie and Moore 1986, Sagnes 1997, Smith and Walker 2003, Paradis et al 2007, Florin and Lingman 2008, Wessels et al 2010, Lee et al 2012, or length-weight relations (Al-Hassan et al 2000, Ogle 2009, Beamish et al 2011). To our knowledge, few studies explore the effect of preservation by taking advantage of the benefits of geometric morphometrics (BerbelFilho et al 2013, Gaston et al 2013.…”