Evidence of denticles and attachment fibres in the superficial layer of scales in two fishes: Carassius auratus and Cyprinus carpio (Cyprinidae, Teleostei)

Scale characteristics of two fish species, Acanthopagrus bifasciatus (Forsskål, 1775) and Rhabdosargus sarba (Forsskål, 1775) from the Red Sea at Jeddah, Saudi Arabia

The present work aimed to screening and documenting the diversity of scale characteristics of two species belonging to two different genera of the family Sparidae: Acanthopagrus bifasciatus and Rhabdosargus sarba from the Red Sea. The valid useful scale characters for systematic purposes were determined in the term of morphometry and Scanning Electron Microscopic techniques. A wide spectrum of size-free intraspecific variations between different body regions was recorded in each species in terms of morphometric indices. The scale characters included the overall form of the scales and their morphometrics, radii counts, shape of interradial tongues, the first circuli, form of interradial circuli and their denticles, the outer lateral and inner lateral circuli and the form of their denticles, granulation of the caudal field and the shape of ctenii. Moreover, the form of the lateral line canal, the relative position of their anterior and posterior openings and the cantilevered anterior extension of the canal were valid in differentiation between species.

Structural peculiarities of the tubercles in the skin of the turbot, Scophthalmus maximus (L., 1758) (Osteichthyes, Pleuronectiformes, Scophthalmidae)

The structure of the bony tubercles of the turbot, Scophthalmus maximus (L., 1758), was examined using ground sections, microradiography, SEM, and TEM. The tubercles are small, isolated, mineralized conical plates randomly distributed in the eyed side of the body. They are composed of three layers: the outer limiting layer, the external layer, and the basal plate, which make up the thin and flat elasmoid scales of Teleostei. The main difference between regular elasmoid scales and bony tubercles lies in the organization and the growth of the basal plate. Indeed, the conical shape of the tubercle is the result of a prominent thickening of the central part of the basal plate where the collagen matrix is organized in a complicated three-dimensional network. Densely packed thick collagen fibrils form superimposed plies organized in a plywood-like structure that resembles that of the elasmoid scales but it is criss-crossed by numerous vertical sheets of thin collagen fibrils. The tubercles originate from thin and flat plates located in the skin of larvae and juveniles, whose structure is that of regular-developing elasmoid scales. Thus, the tubercles of Scophthalmus maximus could be considered as modified elasmoid scales rather than bony structures. They might be the result of specific arrangements related to the general trend of reduction of the dermal skeleton in the teleostean lineage.

Fish scale-induced dermatitis

BACKGROUND

Fish scales loosened during the process of cleaning that come in contact with human skin will adhere and "grow," creating a raised skin lesion if not washed off immediately.

OBJECTIVE

The purpose of this study was to examine the process of fish scale-induced dermatitis.

METHODS

Fish scales from the blue gill (Lepomis machrochirus) were placed on the intact skin of denuded Swiss Webster mice that had no prior sensitization.

RESULTS

The scales physically adhered and formed a raised fold of skin within minutes after placement. Lesions were submitted for pathologic evaluation on days 2 and 7. A subacute irritant dermatitis was observed that evolved into a chronic dermatitis with hyperkeratosis. Inverted fish scales (the anatomically reversed surface) and fish epidermis did not produce such lesions on the mice.

CONCLUSION

Fish scales are able to induce an irritant dermatitis. They most likely do so through initial adhesion via mucopolysaccharide secretions.

New data on the structure and the growth of the osteoderms in the reptile Anguis fragilis L. (Anguidae, Squamata)

Light and electron microscopy shows the osteoderms of Anguis fragilis to be small, flat disks located in the dermis along the adult trunk: microradiography established the extent of the mineralization. Each osteoderm coincides exactly with an epidermal fold forming the keratinized scales characteristic of the skin of reptiles. Sections perpendicular to the surface show two mineralized layers differing in histological and histochemical characteristics and in fine structure, although both contain collagen fibrils. The structure of each layer can be related to that of the surrounding dermis. The outer superficial layer located in the loose dermis contains few collagen bundles that form a discontinuous sheet at the upper surface of the osteoderms. This superficial layer appears to be constituted of units separated by furrows and is composed of woven fibered bone. The basal plate comprises stratified lamellae formed of parallel-oriented collagen fibrils; the fibrils of successive lamellae lie at right angles. The densely packed collagen fibrils of the basal plate are distributed similarly to those of the dense dermis within which it lies. This layer exhibits structural and histochemical characteristics of a lamellar bone. The presence of two different layers in the osteoderms of Anguis fragilis may reflect their mode of formation, which consists of the deposit of mineral crystals in the preexisting dermal tissue. This mineralization process, considered as a "metaplastic ossification," may reflect the potentiality retained by the dermis of reptiles to form mineralized structures.

Structure and comparative morphology of camptotrichia of lungfish fins

The present work is devoted to the organization and ultrastructure of the fin rays or camptotrichia of two living Dipnoi (lungfishes) Protopterus and Neoceratodus. In both species, these rods have a dual structure: only the superficial region facing the stratified epidermis is mineralized while the deep one is made of a dense unmineralized network of collagen fibrils forming a permanent pre-osseous tissue. Only the camptotrichia of Neoceratodus is made of cellular bone. This study confirms the structural peculiarities of these camptotrichia when compared to the dermal skeleton of the Actinopterygii constituted by the bony lepidotrichia and the actinotrichia. These results are discussed and compared to fossil dipnoan fin rays.

Ultrastructure of scales in a teleost (Carassius auratus L.) after use of rapid freeze-fixation and freeze-substitution

New data on the ultrastructural features of the elasmoid scales of Carassius auratus have been obtained by use of rapid freezing with subsequent freeze-substitution in anhydrous solvents. These are compared with the results obtained using conventional aqueous fixatives. The external layer of the scales is composed of randomly oriented collagen fibres. In the first stages of mineralization, mineral deposits are located in the interfibrillary substance where dense granules appear to be active sites of mineralization. Spheritic mineralization occurs in this layer. The fibrillary plate is composed of two kinds of collagen fibres. Most of them are organized in lamellae forming the "plywood-like structure". They are thicker than the so-called "TC fibres", which are oriented from the basal part towards the superficial layer. These TC fibres are involved in the first stages of mineral deposition in the fibrillary plate where inotropic mineralization occurs. The mineral phase is almost always located in the interfibrillary matrix in both layers of the elasmoid scale. In this respect, teleost scales differ from those described so far in other lower vertebrates.