In-depth histological, lectin-histochemical, immunohistochemical and ultrastructural description of the olfactory rosettes and olfactory bulbs of turbot (Scophthalmus maximus)

Abstract

Chemical communication through olfaction is crucial for fish behaviours, particularly in the seabed environment, mediating in socio-sexual behaviours as reproduction. Turbot, a flatfish with significant aquaculture production, possesses a well-developed olfactory system from early developmental stages. After metamorphosis, flatfish undergo significant morphological changes, acquiring the characteristic bilateral asymmetry of the order Pleuronectiformes. This results in the emergence of an ocular side facing the open water column, housing the dorsal olfactory rosette, and a blind side in contact with the sea bottom where the ventral rosette is located. This study aims to address the existing gap in specific histological, lectin-histochemical and immunohistochemical studies of the turbot olfactory rosettes and olfactory bulbs. Additionally, due to the small cell size and high cell density, we enhanced the characterization of the adult olfactory epithelium through transmission electron microscopy. We observed no discernible variations in the olfactory epithelium between rosettes, except for the dorsal rosette being larger in size compared to the ventral rosette. Our study involved the description of the olfactory system in premetamorphic larvae and microdissected olfactory organs of adult turbots using routine histological staining techniques, and a wide array of lectins and primary antibodies against G-proteins and calcium-binding proteins. The results obtained significantly enrich the scarce morphological and neurochemical information available on the turbot olfactory system, revealing a highly complex olfactory epithelium with distinct features compared to other teleost species, especially with regard to olfactory cell distribution and immunolabelling patterns.