Essence of keratin in lips and associated structures of a freshwater fish Puntius sophore in relation to its feeding ecology: histochemistry and scanning electron microscope investigation

Trophic transfer patterns of arsenic in freshwater ecosystem layers in arsenic-endemic Ganges Delta and its potential human health risk

Arsenic (As) is a toxic environmental contaminant with global public health concern. In aquatic ecosystems, the quantification of total As is restricted chiefly to the individual organisms. The present study has quantified the total As in different trophic layers (sediment-water-phytoplankton-periphyton-zooplankton-fish-gastropod-hydrophytes) of lentic freshwater ecosystems. As transfer pathways quantifying the transmission rate across trophic-level compartmental route were delineated using a novel model-based approach along with its potential contamination risk to humans. Lentic water bodies from Indo-Gangetic region, a core area of groundwater As, were selected for the present investigation. The study revealed that among the lower biota, zooplankton were the highest accumulator of total As (5554-11,564 µg kg-1) with magnification (rate = 1.129) of the metalloid, followed by phytoplankton (2579-6865 µg kg-1) and periphytic biofilm (1075 to 4382 µg kg -1). Muscle tissue of zooplanktivore Labeo catla is found to store higher As (80-115 µg kg-1 w.w.) compared to bottom-dwelling omnivore Cirrhinus mrigala (58-92 µg kg-1 w.w.). Whereas, Amblypharyngodon mola has accumulated higher As (203-319 µg kg-1 w.w.) than Puntius sophore (30-98 µg kg-1 w.w.) that raised further concern. The hepatic concentration indicated arsenic-mediated stress based on As stress index (threshold value = 1). Mrigal and Mola showed significant biomagnification among fishes while biodiminution was observed in Catla, Bata, Rohu and Punti. All the studied fishes were under the arsenic mediated stress. In the 'sediment-water-periphytic biofilm-gastropod' compartment, the direct grazing accumulation was higher (rate = 0.618) than the indirect path (rate = 0.587). Stems of edible freshwater macrophytes accumulated lesser As (32-190 µg kg-1 d.w.) than roots (292-946 µg kg-1 d.w.) and leaves (62-231 µg kg-1 d.w.). The target cancer risk (TCR) revealed a greater concern for adults consuming edible macrophyte regularly. Similarly, the varied level of target hazard quotient and TCR for adults consuming fishes from these waterbodies further speculated significant health concerns. The trophic transfer rate of environmental As in soil-water-biota level at an increasing trophic guild and consumer risk analysis have been unravelled for the first time in the Indo-Gangetic plains, which will be helpful for the strategic mitigation of As contamination.

Epidermal modifications in a hill stream catfish, Hara hara in relation to its natural habitat: A scanning electron microscope and histochemical investigation

In the present study, the epidermis of the hill stream fish Hara hara has been investigated employing scanning electron microscope, histology, histochemistry and immunofluorescence techniques. The epidermis is characteristically differentiated into plaques separated from each other by deep furrows. In plaques, the epidermis is keratinized. In contrast, in furrows, it is mucogenic. Surface epithelial cells in plaques get modified into characteristic spine-like unculi. At the distal ends of these unculi, we find tree-like branched dendritic structures. The keratinized epithelial cells in plaques together with unculi frequently exfoliate at the surface. The epidermis in furrows is equipped with secretory glandular cells, that is, mucous goblet cells, sacciform cells and club cells; and sensory structures, that is, the taste buds. These glandular cells are involved in the elaboration of different types of carbohydrate and protein moieties. Further, in the epidermis of both, plaques and furrows, melanophores are frequently interspersed between the epithelial cells. In the plaque epidermis, in addition to melanophores, melanin granules are observed in epithelial cells undergoing keratinization as well as in those sloughing at the surface. Sloughing of keratinized epithelial cells together with spine-like unculi at the surface of the plaques; the secretions of the glandular cells, the distribution of melanophore and the taste buds interspersed between the epithelial cells and the presence of melanin granules in the keratinized epithelial cells have been associated with different functional roles. These include hydrodynamic advantage, protection from mechanical stress, pathogens, UV radiation, localization of food accurately and so on in relation to the natural habitat of the fish.

Lip service: Histological phenotypes correlate with diet and feeding ecology in herbivorous pacus

Complex prey processing requires the repositioning of food between the teeth, as modulated by a soft tissue appendage like a tongue or lips. In this study, we trace the evolution of lips and ligaments, which are used during prey capture and prey processing in an herbivorous group of fishes. Pacus (Serrasalmidae) are Neotropical freshwater fishes that feed on leaves, fruits, and seeds. These prey are hard or tough, require high forces to fracture, contain abrasive or caustic elements, or deform considerably before failure. Pacus are gape-limited and do not have the pharyngeal jaws many bony fishes use to dismantle and/or transport prey. Despite their gape limitation, pacus feed on prey larger than their mouths, relying on robust teeth and a hypertrophied lower lip for manipulation and breakdown of food. We used histology to compare the lip morphology across 14 species of pacus and piranhas to better understand this soft tissue. We found that frugivorous pacus have larger, more complex lips which are innervated and folded at their surface, while grazing species have callused, mucus-covered lips. Unlike mammalian lips or tongues, pacu lips lack any intrinsic skeletal or smooth muscle. This implies that pacu lips lack dexterity; however, we found a novel connection to the primordial ligament which suggests that the lips are actuated by the jaw adductors. We propose that pacus combine hydraulic repositioning of prey inside the buccal cavity with direct oral manipulation, the latter using a combination of a morphologically heterodont dentition and compliant lips for reorienting food.

Scanning electron microscopic and histological studies of the buccal cavity of a phytoplanktivorous small freshwater fish, Amblypharyngodon mola

The electron microscopic and histological studies of the buccal-cavity of herbivorous fish Mola (Amblypharyngodon mola) were performed. The studies revealed that the architectures of the buccal cavity of A. mola support the herbivory nature of the fish. Both the upper and lower jaws of the fish are rich in mucus glands, unculi, and microridges. The presence of papillae like taste buds in the lower jaw of A. mola indicates the mechanosensory role of the lower jaw during gustation. These features directly support a gustatory feeding behavior associated with filter feeding in this small freshwater fish.

The microstructure of buccal cavity and alimentary canal of Siganus rivulatus: Scanning electron microscope study

The microstructure of the oral cavity and alimentary canal of herbivorous fish Siganus rivulatus collected from the Red Sea were investigated by using scanning electron microscope (SEM). The results showed that S. rivulatus has three types of teeth, tri-cusped, bi-cusped, and papilliform. A taste bud (Type I) was recorded in the oropharyngeal cavity. Characteristic styles of microridges on the cell's surface inside the buccal cavity were recorded. Also, the distribution of the mucous cells in the lining of the mouth cavity, alimentary canal was observed. Mucosal folds along the distinct parts of alimentary canal, showed characteristic pattern which was complex in the intestinal mucosa. The results concluded that there are characteristic microstructures according to feeding habitat compared with other bony fishes.

Keratinization and mucogenesis in the epidermis of an angler catfish Chaca chaca (Siluriformes, Chacidae): A Histochemical and fluorescence microscope investigation

The present study describes keratinization and mucogenesis in the epidermis of an angler catfish Chaca chaca, using a series of immunochemical, fluorescence and histochemical methods. The epidermis is primarily mucogenic and shows characteristic specialised structures at irregular intervals. These structures are identified keratinized in nature. The superficial layer epithelial cells in the keratinized structures often detach from the underlying epithelial cells and exfoliate either singly or in the form of sheet. This is associated to provide protection by removing silty depositions, pathogens, and debris along with exfoliated keratinized cells/sheets periodically to keep the skin surface clean. Mucogenic epidermis is equipped with the mucous goblet cells and the club cells. Nevertheless, these cells are not discernible in the keratinized structures. This suggests an inverse relationship between mucogenesis and keratinization in the epidermis of the fish. The mucogenic epidermis is involved in the secretion of different classes of glycoproteins. These include glycoproteins with oxidizable vicinal diols, glycoproteins with O-sulphate esters and glycoproteins with sialic acid residues without O-acyl substitution. Secretion of these glycoproteins on the surface are associated to control the acidity of the acidic glycoproteins, to protect the skin surface against bacterial, viral infection and other pathogens, and help in lubrication to protect against abrasion during burrowing. Epidermal keratinization and glycoprotein characterization are associated with the physiological adaptations in relation to the characteristic habit and habitat of the fish.

A functional evaluation of feeding in the surgeonfish Ctenochaetus striatus: the role of soft tissues

Ctenochaetus striatus is one of the most abundant surgeonfishes on Indo-Pacific coral reefs, yet the functional role and feeding ecology of this species remain unclear. This species is reported to possess a rigid structure in its palate that is used for scraping, but some authors have reported that this element is comprised of soft tissue. To resolve the nature and role of this structure in the feeding ecology of C. striatus we examined evidence from anatomical observations, scanning electron microscopy, histology, X-ray micro-computed tomography scanning, high-speed video and field observations. We found that C. striatus from the Great Barrier Reef possess a retention plate (RP) on their palates immediately posterior to the premaxillary teeth which is soft, covered in a thin veneer of keratin with a papillate surface. This RP appears to be used during feeding, but does not appear to be responsible for the removal of material, which is achieved primarily by a fast closure of the lower jaw. We infer that the RP acts primarily as a 'dustpan', in a 'dustpan and brush' feeding mechanism, to facilitate the collection of particulate material from algal turfs.

Tgm1-like transglutaminases in tilapia (Oreochromis mossambicus)

Among the adaptations of aquatic species during evolution of terrestrial tetrapods was the development of an epidermis preventing desiccation. In present day mammals, keratinocytes of the epidermis, using a membrane-bound transglutaminase (Tgm1), accomplish this function by synthesizing a scaffold of cross-linked protein to which a lipid envelope is attached. This study characterizes the abilities of two homologous transglutaminase isozymes in the teleost fish tilapia to form cross-linked protein structures and their expression in certain tissues. Results indicate they are capable of membrane localization and of generating cellular structures resistant to detergent solubilization. They are both expressed in epithelial cells of the lip, buccal cavity and tips of gill filaments. Adaptation of transglutaminase use in evolution of terrestrial keratinocytes evidently involved refinements in tissue expression, access to suitable substrate proteins and activation of cross-linking during terminal differentiation.

Morphological study of the asymmetrical buccal cavity of the flatfish common solea (Solea solea) and its relation to the type of feeding

OBJECTIVE

To investigate the surface architecture of the asymmetrical buccal cavity of Solea solea which are considered one of the most important predators in benthic communities.

METHODS

Adult Solea solea were obtained from Mediterranean Sea near Damietta. The heads were removed and processed for scanning electron microscopy. Its buccal cavity is asymmetrical and divided into roof and floor and the tongue for histological studies.

RESULTS

The buccal cavity roof is formed from upper jaw, velum and the palate. The upper jaw has several wing like processes with teeth arranged in several rows which may help in cutting and pushing the food to the entrance of the digestive canal while the floor is formed from the lower jaw and the tongue. The tongue is divided into apex, body and root. There is a gradual decrease of goblet cells in the tongue from anterior to posterior. These goblet cells function in protection of the epithelium.

CONCLUSIONS

Teeth in the floor of the buccal cavity and taste buds can be considered adaptive changes of the oral cavity related to the feeding habits and was a source to identify new and better methods of nutrition in aquaculture of Solea solea.

Chicken corneocyte cross-linked proteome

Shotgun proteomic analysis was performed of epidermal scale, feather, beak and claw from the domestic chicken. To this end, the samples were separated first into solubilized and particulate fractions, the latter enriched in isopeptide cross-linking, by exhaustive extraction in sodium dodecyl sulfate under reducing conditions. Among the 205 proteins identified were 17 keratins (types α and β), 51 involved in protein synthesis, 8 junctional, 8 histone, 5 heat shock, and 5 14-3-3 proteins. Considerable overlap among the beak, claw, feather, and scale samples was observed in protein profiles, but those from beak and claw were the most similar. Scale and feather profiles were the most distinctive, each exhibiting specific proteins. Less than 20% of the proteins were found only in the detergent-solubilized fraction, while 34-57% were found only in the particulate fraction, depending on the source, and the rest in both fractions. The results provide the first comprehensive analysis of the content of these cornified structures, reveal the efficient use of available proteins in conferring mechanical and chemical stability to them, and emphasize the importance of isopeptide cross-linking in avian epithelial cornification.