Effect of preservation on fish morphology over time: Implications for morphological studies

Abstract

It has long been recognized that the process of preserving biological specimens results in alterations of body shape, though detailed studies examining the degree to which morphological changes occur throughout the preservation process are lacking. We utilize geometric morphometric analyses, an increasingly common tool for examining shape variation in a wide variety of biological disciplines, to examine the effects of formalin and ethanol preservation on the body shape of 10 freshwater fish species over time: from fresh specimens to eight weeks after preservation. We found significant changes in body shape among fresh and formalin fixed specimens. Furthermore, changes in body shape continue to occur after subsequent ethanol preservation. Two fish species collected at multiple localities show significant morphological differences for a limited number of morphometric characters. However, the significance, or lack thereof, often changed inconsistently from one stage of preservation to another. We conclude that morphometric analyses would ideally be performed on fresh specimens. However, recognizing that this is not always feasible, it is important to be aware of the morphometric changes that can occur during preservation.

Eye size and investment in frogs and toads correlate with adult habitat, activity pattern and breeding ecology

“…Using museum specimens to quantify eye and body size presents two potential problems: (i) external eye diameter measurements may not be as accurate as measurements on dissected whole eyes, and (ii) fixation and preservation may alter tissue sizes and shapes (e.g. [42]), potentially introducing error into allometric scaling relationships. Ideally, we would avoid these issues by using fresh specimens, but this was not feasible for the taxonomic range of species in our analyses.…”

Length‐weight relationships of six fish species from the Xiangjiang River in Guangxi region, China

“…Recent studies reported that formalin fixation may be linked to a certain shrinking effect on fish bodies and loss of mass (Anzueto‐Calvo et al., 2017; Buchheister & Wilson, 2005; Campos et al., 2020). This effect can be directly associated with the abnormal values of the LWR parameters (Anzueto‐Calvo et al., 2017) and lead to a higher allometric coefficients (Machado et al., 2020), so it is important to be conscious of the changes of length and weight that occur during preservation (Sotola et al., 2019). Although all coefficients of allometry of the species analyzed in this study are within the general range for fishes (2.5 ≤ b ≤ 3.5; Froese, 2006), further studies should focus on measuring and weighing fish in fresh condition to reduce the impact of preservation of the specimens, which could estimate LWRs more accurate.…”

Length–weight relationships of six fish species from mangroves of Qinzhou Harbor, Southern China

“…Although the measure of standard length and total weight for fish samples were within 1 week after the preservation of formaldehyde (10%), the affect of preserved in formalin needed to be considered, especially there are some small‐size fish samples (Nordeide, 2020; Sotola et al., 2019). Studies show that formalin has an effect on body shrinkage and loss of mass (Anzueto‐Calvo et al., 2017; Buchheister & Wilson, 2005), and lead to the allometric coefficients higher (Machado et al., 2020), so it is important to be conscious of the length and weight changes that occur during preservation (Sotola et al., 2019). Further studies should focus on measuring and weighing fish in fresh condition to reduce the impact of preservation of the specimens, which could estimate LWRs more accurate.…”