Skeletal Anomalies in Senegalese Sole (Solea senegalensis), an Anosteocytic Boned Flatfish Species

Abstract

Skeletal anomalies affect animal welfare and cause important economic problems in aquaculture. Despite the high frequency of skeletal problems in reared Solea senegalensis, there is lack of information regarding the histological features of normal and deformed vertebrae in this flatfish. The aim of this study was to describe the histopathological and radiographical appearance of vertebral body anomalies. Sixty-seven juvenile fish were radiographically examined 104 or 105 days after hatching. Through radiographic images, vertebral segments were selected and processed for histopathological examination from 7 normal and 7 affected fish. Alterations in bone shape and vertebral fusion were the most significant anomalies in the vertebral bodies. These alterations occurred most frequently between the last 3 abdominal vertebrae and the first 10 caudal centra. Radiographically, deformed vertebrae showed flattening of the endplates and narrowing of the intervertebral spaces. The radiographic findings concurred with the histological lesions where affected vertebrae exhibited irregular endplates and changes in trabecular bone. Radiolucent cartilaginous tissue was evident in the endplates of the deformed vertebra and, in some cases, the cartilaginous material extended from the growth zone into the intervertebral space. These changes were likely the primary alterations that led to vertebral fusion. Fused vertebrae were often reshaped and showed a reorganization of the trabeculae. The formation of metaplastic cartilage is frequent in a variety of anomalies affecting teleost species.

Deformity or variation? Phenotypic diversity in the zebrafish vertebral column

“…In zebrafish, the urostyle is the result of five or rather six fusion events, as can be inferred from the presence of supernumerary modified haemal arches/spines (hypurals) (Bensimon‐Brito, Cardeira, et al, 2012; Wiley et al, 2015). On the other hand, fusion of vertebral centra anterior to the caudal fin endoskeleton is a common pathology in reared teleosts (Cotti et al, 2020; de Azevedo et al, 2019; Martini et al, 2021; Witten et al, 2006, 2009; Ytteborg et al, 2010). Although its aetiology is often unknown, some possible causative factors have been identified, such as temperature, rearing density, and high dietary phosphorous content (Cotti et al, 2020; Martini et al, 2021; Ytteborg et al, 2010).…”

“…In zebrafish, the urostyle is the result of five or rather six fusion events, as can be inferred from the presence of supernumerary modified haemal arches/spines (hypurals) (Bensimon-Brito, Cardeira, et al, 2012;Wiley et al, 2015). On the other hand, fusion of vertebral centra anterior to the caudal fin endoskeleton is a common pathology in reared teleosts (Cotti et al, 2020;de Azevedo et al, 2019;Martini et al, 2021;Witten et al, 2006Ytteborg et al, 2010).…”

“…Some of the phenotypes described here are to be considered normal intraspecific variation, as they occur frequently and are the truncated outcome of developmental programmes that produced the character as a normal element of the Bauplan in ancestral species (and thus could appear as vestigial characters), whilst others are to be considered anomalies. The vertebral fusions resemble those which occur both as a normal part of development as well as occurring as a pathology (Cotti et al, 2020;de Azevedo et al, 2019;Martini et al, 2021;Witten et al, 2006Ytteborg et al, 2010). They could be considered as both, depending on the position within the vertebral column.…”

Genetic Estimates for Growth and Shape-Related Traits in the Flatfish Senegalese Sole

“…In the case of Senegalese sole, body shape is expected to be highly elliptic and lanceolate with short jaws and long dorsal and anal fins that contrast with the shape of most pleuronectids or scophthalmids with deeper bodies, longer jaws and short dorsal and anal fins. However, several reports that dealt with morphological traits in Senegalese sole in aquaculture reported high rates of malformations that in most cases do not have a severe impact on external gross morphology [ 4 , 6 , 7 , 8 ]. In this study, we investigate for first time in Senegalese sole the phenotypic and genetic variation associated with shape-related traits under industrial conditions in RAS.…”

“…However, this species exhibits a high plasticity of the skeletal components, such as the vertebral number, which oscillates between 44 and 48 (mode = 45) with 8–9 in the abdominal region, 34–35 in the caudal region and 3–4 in the caudal complex [ 4 , 5 ]. Moreover, this species is highly prone to vertebral abnormalities and other skeletal malformations that can reach even more than 70% of individuals in cultured populations, most of them corresponding to vertebral fusions in the caudal region and deformities in the caudal complex [ 4 , 6 , 7 , 8 , 9 ]. Most of these malformations are usually externally unnoticed or they have a moderate effect on gross phenotypic morphology (approximately 46% of animals with vertebral deformities were categorized as normal) [ 4 ].…”