Morphological Examination of Vertebral Bodies (Centrum) From Grass Carp (Ctenopharyngodon idella) Using High‐Resolution Micro‐CT Scans

Abstract

The vertebral column, a defining trait of all vertebrates, is organized as a concatenated chain of vertebrae, and therefore its support to the body depends on individual vertebral morphology. Consequently, studying the morphology of the vertebral body (centrum) is of anatomical and clinical importance. In this study, we have investigated the morphology of Grass carp (Ctenopharyngodon idella) vertebral centrum using high‐resolution micro‐CT scans. Grass carp is a member of the interclass Teleostei (teleost fish), part of the class Actinopterygii, which accounts for the majority of all vertebrate species; thus, Grass carp vertebral morphology can help us understand normal vertebrate vertebral morphology and development. Based on previous studies done on teleost fish, we hypothesized that vertebral centrum will demonstrate bilateral symmetry along the sagittal (left/right) and transverse (cranial/caudal) planes. To this end, three vertebrae (numbers V9‐11) from eight Grass carps that were housed in a Living Stream Systems for 8 weeks at 15⁰C were harvested and micro‐CT scanned at a resolution of 19.29 µm (SkyScan1173, Bruker Inc). The scans were reconstructed into 16‐bit TIFF image stacks and then imported into Dragonfly (ORS Inc.) for segmentation using an Otsu algorithm. After centering each vertebrae along its three principal axes various morphological measurements were performed. Grass carp vertebral centrum demonstrated an hourglass shape where both endplates are concave. While the vertebral centrum demonstrated bilateral symmetry along the sagittal plane (left/right, in line with our hypothesis), vertebral centrum demonstrated deviation from bilateral symmetry along the transverse plane (cranial/caudal, refuting our hypothesis). The vertebral centrum cranial endplate size (perimeter and area) was found to be smaller and less circular compared to the caudal endplate. This implies that the vertebral body tapers off from caudal to cranial. In addition, the cranial endplate was found to be shallower (i.e. more obtuse angles, α > β, see figure 1) compared to the caudal endplate. As a result of the shallower cranial endplate, the center of the vertebrae (narrowest part of the hourglass, between the two endplates) was shifted cranially (A < B, see figure 1). The sum of these findings implies that the caudal aspect of Grass carp vertebral centrum is bigger and more robust. Currently we have no information whether this is due to nature, e.g. differences in gene expression, or nurture, e.g. environmental effect. As the vertebral transverse and spinous processes are slanted caudally, the direction of muscle action during swimming may create a gradient of stresses from cranial to caudal, resulting in a more robust caudal aspect of the vertebral centrum. Expanding our study to include additional quadrupedal and bipedal (i.e. humans) vertebrae, as well as testing if these morphological aspects of the vertebrae are indeed plastic and can be affected by environmental factors (i.e. temperature or other stressors) may help answering this interesting question.