Anatomical, histological and immunohistochemical study of the tongue in the rainbow trout (Oncorhynchus mykiss)

Abstract

The rainbow trout (Oncorhynchus mykiss Walbaum, 1792) is a fish commercially farmed all over the world. These fish are usually fed, in aquaculture, with pellets rich in proteins and fat. It is well known that there are close relationships among the adaptation of vertebrates to their environment, the capacity and the modality of feeding and the oral cavity morphology, especially the tongue one. No data are so far available about the morphology of the rainbow trout tongue, and therefore, the aim of this study was to investigate by light, scanning electron and confocal laser microscopy, the morphological characteristics of the tongue. An apex, a body and a root can be distinguished in the tongue, and the presence of teeth, taste buds and fungiformlike papillae was demonstrated. Light microscopy shows the presence of an adipose tissue pad in the deeper layer of the apex and in the most superficial layer of the root. In the deeper layer of the body, a triangular-shaped pad consisting of fusiform cells immersed in abundant extracellular matrix of the mesenchymal tissue was observed. The confocal laser microscopy shows the presence of cells with a fibroblast-like morphology positive for vimentin. In the deepest layer of the tongue root, a large area of osteo-cartilaginous tissue was observed. The results, besides the description of the morphological characteristics of the tongue, related to studies regarding the feeding, could be considered for the eventual applications of the use of mesenchymal cells, observed in adult fish, in cell therapies in different pathologies.

Morphological characteristics of the blackspot seabream (Pagellus bogaraveo) tongue: A structural and immunohistochemical study

“…Tissue samples of 5 fresh specimens (3 male and 2 female) were fixed in Bouin fixative for 24 hr, dehydrated and routinely embedded in paraffin. As in previous studies on tongue (Abbate et al, 2006(Abbate et al, , 2017(Abbate et al, , 2020b(Abbate et al, , 2020a(Abbate et al, , 2012b(Abbate et al, , 2012a, about 10 µm thick transversal, horizontal and sagittal serial sections were obtained using Leica RM 2135 microtome (Leica microsistems Nussloch GmbH).…”

The Alimentary Tract of African Bony-Tongue, Heterotis niloticus (Cuvier, 1829): Morphology Study

“…The posterior intestine, however, was defined as the tract starting from the second fold of the intestine until the 45° curved part of the intestine which represents the rectum, ending up in the anus. The organs were processed for routine histological study (dehydration, diaphanization, and paraffin embedding (for the technique in detail see [ 22 , 23 ]). The histological investigation was carried out on the esophagus, stomach, intestine and pyloric caeca, which in turn were divided into three, two (proventriculus and ventriculus), four (anterior, intermediate, posterior, and rectum) and eight segments respectively.…”

“…The oropharyngeal cavity of vertebrates plays an important role in the collection and initial processing of food [ 19 , 20 ]. Adaptive morphological changes are present in the oropharyngeal cavity of different fishes strictly related to the feeding habits of the fish [ 21 , 22 , 23 , 24 , 25 ]. The tongue, which in most fish species is defined as a thickening of the floor of the mouth [ 26 , 27 ], in some species is described as a real taste organ due to the presence of taste buds scattered on its dorsal surface, demonstrating a gustatory ability [ 28 , 29 , 30 , 31 , 32 ].…”

“…Those findings can be explained by the nature of the diet, in particular, the number of vegetal materials in diets [ 18 , 38 ]. Numerous comparative studies with other vertebrate species such as birds and reptiles are present in the literature [ 20 , 22 , 23 , 32 , 39 , 40 , 41 , 42 , 43 , 44 ]. Although few data concerning the digestive tract of African bony-tongue are present in the literature [ 45 , 46 ], they appear incomplete with minimal descriptions of both gross anatomy and histological features.…”

Involvement of Taste Receptors in the Oro-Sensory Perception of Nutrients in Rainbow Trout (Oncorhynchus mykiss) Fed Diets with Different Fatty Acid Profiles

“…However, research for the oro-detection of long-chain fatty acids have been mainly conducted on rodent models as well as on human taste bud cells [23] but remains poorly studied in fishes [24]. Hovewer, the description of the morphological characteristics of the tongue of RT has recently been published [25]. The study revealed orogustatory structures common to mammals (the presence of taste bud cells), but the molecular mechanism underlying the lingual detection of nutrients has not been elucidated in fishes.…”