Spinal Abnormalities in a Specimen of the Panamanian Knifefish Apteronotus rostratus (Apteronotidae: Gymnotiformes) with Comments on Gymnotiformes Locomotion

Skeletal deformities among fishes are well documented in the aquaculture industry and husbandry studies. However, these deformities are noticeably less prevalent among wild caught animals, likely due to their deleterious effects on the fitness of affected individuals particularly at earlier life-history stages. Here we use micro-CT imaging to describe, for the first time, spinal abnormalities in a Neotropical electric fish (Apteronotus rostratus). We find that the deformed specimen exhibits scoliosis and kyphosis of pre-caudal vertebrae 11-14 and an additional fusion of a hemal spine into the descending blade of the anterior displaced hemal spine. We also find that the abnormal specimen was able to reach sexual maturity and forage effectively (as evidenced by ripe ovaries and the presence of insect larvae in the digestive tract) despite exhibiting several spinal deformities. We infer that a highly specialized form of gymn_168.tiform locomotion allowed the deformed specimen to reach maturity and avoid predation in the face of these abnormalities.