The Vertebral Column of Flatfish: A Review

Flatfish (Pleuronectiformes) encompass fascinating fish species known for their high gastronomical value, rearing performances, and market prices, which attract both economic and scientific interest. Despite these attributes, flatfish exhibit unique morphological, developmental, and biological features, as well as distinctive swimming movements, which require special approaches in skeletal biology research, an area that remains relatively unexplored for this diverse group of fishes. These unique features emerge during metamorphosis, at the end of the larval period, when bilateral symmetric pelagic larvae gradually become asymmetric and undergo various morphological and physiological changes. Consequently, the skeletal characteristics of these species include a certain degree of asymmetry in the skeletal structures. These fish also present acellular bone (bone devoid of osteocytes). Research on flatfish skeletons is crucial for improving animal welfare and promoting sustainable farming, as the literature indicates that more than 50% of the larvae and juveniles of different cultured flatfish can be affected by skeletal deformities. This review aims to compile the available studies on the development of vertebral column deformities in flatfish in an integrative manner, addressing state-of-the-art research on the etiology, diagnostics, and innovative studies on this issue. It also covers the fundamental aspects of teleost skeletal development, particularly the flatfish vertebral column.