Quantitative Assessment of Brain Volumes in Fish: Comparison of Methodologies

Abstract

When correlating brain areas with behavioral and environmental characteristics, a variety of techniques are employed. In fishes (elasmobranchs and teleosts), 2 methods, histology and the idealized ellipsoid and/or half-ellipsoid technique, are primarily used to calculate the volume of a brain area and therefore its relationship to social or ecological complexity. In this study on a perciform teleost, we have quantitatively compared brain volumes obtained using the conventional techniques of histology and approximating brain volume to an idealized ellipsoid (or half ellipsoid) and magnetic resonance imaging, an established clinical tool typically used for assessing brain volume in other vertebrates. Our results indicate that, when compared to brain volumes measured using magnetic resonance imaging of brain regions in situ, variations in brain shape and histological artifacts can lead to significant differences in brain volume, especially in the telencephalon and optic tecta. Consequently, in comparative studies of brain volumes, we advise caution when using the histological and/or ellipsoid methods to make correlations between brain area size and environmental, behavioral and social characteristics and, when possible, we propose the use of magnetic resonance imaging.

Allometric Scaling of the Optic Tectum in Cartilaginous Fishes

“…material, see www.karger.com/doi/10.1159/000339875). For method E, it was assumed that each of the bilateral lobes of the tectum takes the form of an idealized half-ellipsoid [Huber et al, 1997;Wagner, 2001a, b;Lisney and Collin, 2006;Pollen et al, 2007;Ullmann et al, 2010]. Linear measurements of the length (l) , width (w) and height (h) of the left tectal lobe were made directly using digital calipers or were measured from digital photographs of the dorsal and lateral (left) aspects of each brain, using Image J [Rasband, 1997[Rasband, -2011 ( fig.…”

“…In some species, the cerebellar corpus covered the dorsal aspect of the optic tectum, so this brain area was removed prior to making measurements. The width of the lobe was defined as described in Ullmann et al [2010], while the length was defined as a line parallel to the sulcus tectotegmentalis (which delineates the tectum from the underlying tegmentum Smeets, 1998]) and extends the maximum length of the structure. The height was defined as a line that extends perpendicularly from the dorsal surface to the sulcus tectotegmentalis.…”

“…from histological coronal sections and magnetic resonance imaging, or MRI) have found that the ellipsoid and half-ellipsoid methods can result in an overestimation of the volume of a brain area in fishes [Pollen et al, 2007;Ullmann et al, 2010]. For the 45 species from which we were able to measure optic tectum volume using both method E and method S, it was possible to assess the variation between the two methods and to calculate correction factors.…”

“…These include gross dissection [Northcutt, 1977[Northcutt, , 1978Yopak et al, 2007;Lisney et al, 2008], the idealized ellipsoid or half ellipsoid approaches, which assume that brain areas take the form of an idealized ellipsoid or halfellipsoid, respectively [Huber et al, 1997;Wagner, 2001a, b;Pollen et al, 2007], serial sectioning (with or without histological staining) and summation of the area of delineated brain regions then multiplied by the section thickness [Northcutt, 1978;Smeets et al, 1983;Brandstätter and Kotrschal, 1990;Kotrschal and Palzenberger, 1992;Yopak et al, 2007], and MRI Ullmann et al, 2010]. In order to avoid drawing misleading conclusions about relationships between brain organization and various ecological niche factors across a range of studies that employ different techniques, it was essential that the measurements quantifying the sizes of various brain areas are comparable, or at the very least, that technique-specific biases are quantified.…”

“…In order to avoid drawing misleading conclusions about relationships between brain organization and various ecological niche factors across a range of studies that employ different techniques, it was essential that the measurements quantifying the sizes of various brain areas are comparable, or at the very least, that technique-specific biases are quantified. For example, a recent study comparing the four methods, the idealized ellipsoid and idealized halfellipsoid methods, conventional sectioning and histology, and MRI, revealed that all four methodologies provide significantly different estimates of volume for the same brain region in the teleost fish Lates calcarifer [Ullmann et al, 2010]. This study highlighted the need for more consistent, quantitative measures of brain structure size, and erred against using ellipsoid and half-ellipsoid approaches.…”