Barbels of the Larval and Adult African Catfish (Clarias gariepinus): Light, Scanning and Transmission Electron Microscopy Investigation

Transcription

1 Barbels of the Larval and Adult African Catfish (Clarias gariepinus): Light, Scanning and Transmission Electron Microscopy Investigation S.A.A. El-Gendy 1,*,Amira Derbalah 2 and Ramy, M. Shourbela 3 1 Department of Anatomy and Embryology, 2 Department of Histology, 3 Dept. of Animal Husbandry and Animal Wealth Development, (Fish breeding and production), Faculty of Veterinary Medicine, Alexandria University, Edfina, El Behera, Egypt With 34 figures Received December 2016, accepted for publication February 2017 Abstract The present study describes the structure of the barbels in larval and adult African catfish. The African catfish has four pairs of barbels. The two types of barbels appear in first-day larvae, without taste buds. The barbels of the third-day larvae had slight folding and their taste buds had few microvilli. In the fifth-day larvae, the taste buds were concave and their microvilli were condensed at the periphery and loosely arranged centrally. Taste buds of the seventh-day larvae appeared as volcano-like elevations with alternative arrangement. In the thirteenth-day larvae, taste buds were placed on the epidermal papillae and they possessed large and small microvilli. The adult catfish barbels consisted of an epidermis, dermis and a central rod of cartilage. The flask-shaped taste buds were scattered among the epidermal cells. By SEM, the epithelial surface appeared as circular whirlpools, the center of each whirlpool was a Mulberry-form taste bud. By TEM, the taste buds consisted of light, dark and basal cells. Interdigitations between light and dark cells and unmyelinated nerve fibers were found in between basal and light cells. Light cells had membranebound vesicles. Basal cells had a ruffled appearance and unmyelinated nerve fibers were noticed among the basal cells. Synapse-like structures were seen in the basal region of the taste buds; due to convergence of these structures we suggest that the dark, light, basal cells and unmylinated nerve fibers act as a modifier in the transmission of taste information from receptor to central nervous system in the dark. Keywords: Ultrastructure, SEM, Barbels, African catfish J. Vet. Anat. 17

2 Introduction Egyptian aquaculture has grown rapidly over the past fifteen years. It provides an important part of the national food supply. The African catfish (Clarias gariepinus) is a common national food and a part of the overall fish supply and demand in Egypt (Ibrahim and El-Naggar, 2010). African catfish production provided 4.4% (31.9 thousand tons a year) of the total Egyptian fish from 1995 to 2007 (Abdel- Hafez and El-Caryony, 2009). The African catfish are piscivorous fish. They possess a great economic importance because they attain a large body size with minimum cost (Elshebly, 2006). The African catfish possesses external appendages named barbels. The barbels are accessory feeding structures that contain sensory organs and they play an essential role in fish activities (Kapoor and Bhargava, 1967; Park et al., 2005, 2006). Barbels fluctuate in number and size. There are many varieties of barbel textures; they may be tender, rigid, without cartilage, with an axial rod of striated muscle, and with or without taste buds (Fox, 1999). The barbels are present on the nasal (Channel catfish) Elaine et al., 2005 and mental (Artedidraco phaine) (Richard,et al.2001) regions. The feeding, direction of swimming, and community behavior of the fish depend on the sense of olfaction especially chemical sensation (Boudriot and Reutter, 2001). The catfish larvae and adults have the ability to feed in the dark and dim light conditions (Hossain et al., 1998), which indicates that their behavior depends on sensory organs other than the eye. C. gariepinus has numerous taste buds and it has been proposed that the taste buds had a role in their rearing behavior Mukai et al. (2008). Our study aims to explain the macro and microstructure of the barbels at the larval and adult stages of African catfish and the functional relation between the different cell units of barbels. Materials and Methods Samples Ten larvae each day from 1-14-dayold larvae and five adult of African catfish were collected from a local fisher hatchery at the Faculty of Veterinary Medicine. The procedures were approved by the ethical committee of Alexandria University, Egypt. For light microscopy The whole larva and small pieces from different parts of barbels of adult African catfish were fixed in 10% neutral buffered formaldehyde for 48 hrs., then dehydrated in ascending grades of ethyl alcohol. They were cleared in xylene and embedded in three changes of paraffin. The paraffin blocks were cut 6 μm thick and stained by J. Vet. Anat. 18

3 Harris hematoxylin and eosin stain (H&E) for standard histological examination (Bancroft and Gamble, 2008) and Masson trichrome stain for the detection of muscular tissue, blood vessels and collagen fiber (Masson, 1929). For scanning electron microscopy The whole larva and small pieces from different parts of barbels of the adult African catfish were immediately immersed in a fixative (2% formaldehyde, 1.25%glutaraldehyde in 0.1 M sodium cacodylate buffer, ph 7.2) at 4 C. Once fixed, the samples were washed in 0.1 M sodium cacodylate containing 5% sucrose, processed through tannic acid, and finally dehydrated in increasing concentrations of ethanol (15 min each in 50,70, 80, 90, 95 and 100% ethanol). The samples were critical-point dried in carbon dioxide and attached to stubs with colloidal carbon then coated with gold palladium in a sputtering device. Specimens were examined and photographed with a JEOL scanning electron microscope operating at 15 Kv. For transmission electron microscopy Small cubes (1 mm3) of barbels from adult catfish were immediately fixed in 6% solution of phosphate-buffered glutaraldehyde, ph 7.4, at 4 C for 6 hrs. (McDowell and Trump,1976). After initial fixation, tissues were washed in several changes of cold (4 C) 0.1 M phosphate buffer every 15 min for 2 hrs. Samples were then rapidly dehydrated through increasing concentrations of ethanol, transferred to propylene oxide and placed over-night in a 1:1 mixture of propylene oxide and epoxy araldite. Semi-thin sections (1 mm) were first cut and stained with toluidine blue and viewed with a light microscope to choose areas suitable for transmission electron microscopy. Ultrathin sections ( nm) were then cut by a glass knife with an L.K.B. micro-tome and stained with uranyl acetate followed by lead citrate (Hayat, 1986). The ultrathin sections were examined with a JEOL transmission electron microscope operating at 100 Kv. Results Light microscopic examination of the 1-day larvae of the African catfish head revealed the presence of a wide yolk sac, encephalic vesicles, an optic cup and the barbels which appeared as miniature protuberances with stratified squamous epithelium (Fig 1). SEM of the 1-day larvae with opened mouth showed the maxillary and outer mandibular barbels as miniature protuberances with expanded membranes toward the rostral region from the angle of the mouth to the ventrolateral part of the lower lip (Fig 2). The origin of the nasal and inner mandibular barbels had slight elevation. The barbels were smooth and J. Vet. Anat. 19

4 had no taste buds. SEM of the 3-day larvae with opened mouth showed four types of barbels. The barbels had slight foldings. The barbels were cylindrical in shape with a tapered external contour and a blunt end (Fig 3). The taste buds were present at the same levels of the surrounding epithelium. The taste buds were characterized by the presence of many pores and few sensory microvilli. Some of the microvilli were thin and others were thick in diameter (Fig 4). Light microscopic examination of the head of 5-day larvae of African catfish showed prominent short and long barbels around the mouth opening. The short barbels had a core of connective tissue surrounded by stratified squamous epithelium. A central axis of cartilage was found in the long barbels (Figs 5&6). By SEM, four pairs of barbels attained a longer cylindrical shape and they were folded. Taste buds were concave and at the top of tucked areas they present (Fig 7), sensory microvilli and pores. The microvilli were condensed mainly at the periphery and loosely arranged mainly at center of the taste buds (Fig 8). Light microscopic examination of the head of 13-day larvae showed that barbels increased in length and a layer of smooth muscle was found near the cartilaginous rod (Fig 9). By SEM, the barbel surface of 7-day larvae showed folded epithelial surfaces and the taste buds alternated along the barbels (Figs 10&12). Taste buds appeared as volcano-like elevations with a folded wall and a rough framework (Fig 14). The barbel surface of 13-day larvae of African catfish exhibited undulant epithelial surfaces with deep ruts (Figs 11&13). Taste buds placed on the epidermal papillae showed conical elevations (Fig 15). Large and small microvilli coated the tip and the surrounding wall of the taste buds (Fig 15). In the adult catfish we observed four pairs of unbranched barbels; one nasal, one maxillary (longest and most mobile) and two mandibulars (inner and outer) on the lower jaw; they were conical in shape with tapered ends (Fig 16). The longest barbels were the maxillary, followed by the outer mandibular and inner mandibular with the shortest being the nasal barbels. The barbels of the African catfish were similar in structure. The barbels were comprised of three main strata: an epidermis and a dermis, in addition to a focal rod of cartilage (Figs 17&18). The epidermal stratum was composed of stratified epithelial cells. It had superficial, middle and basal layers. The superficial layer was characterized by flattened or oval cells (Fig 19) with vacuolated cytoplasm and central nucleus (Fig 19) and the basal layer contained columnar cells (Fig 19).We noted numerous flask-shaped taste buds were scattered among the epidermal cells. A few pigment cells were J. Vet. Anat. 20

5 scattered in the dermis (Fig 20). They consisted of basal cells with centrally located basophilic nuclei and columnar cells with elongated nuclei and lightlystained cytoplasm (Fig 21). By SEM, the epithelial surface of the barbels of adult African catfish appeared to have circular whirlpools; these appeared where epidermal projection was arranged peripherally and at the center of whirlpool where there were taste buds. These taste buds were polyhedral semi-circular forms or oval-shaped (Fig 23). The taste buds appeared as concave discs or they were Mulberry-form with a groove surrounding the taste buds. Epidermal projections were separated by deep furrows. Each epidermal projection had two pits for mucous secretion. It was covered by rough epithelial bristles which gave it a velvety appearance (Fig 24). The concave apex of the taste buds had a central pore and microvilli (Fig 25). The many microvilli appeared at the lateral aspect of the Mulberry-form taste buds (Fig 26). The dermis was composed of numerous collagen fibers, abundant blood vessels, nerve fibers and few pigment cells (Fig 20&30). The chondrocytes were triangular in shape with central nucleus (Fig 21). By TEM, taste buds consisted of three types of cells; light, dark, and basal cells. The light and dark cells were located at the proximal two-thirds of the taste bud, while the distal third of the taste bud was composed of basal cells found adjacent to the basal lamina (Fig 27). The dark cells were elongated and thin with short thick microvilli on their apex. They also showed irregular branching cytoplasmic processes at their lateral surfaces which were interposed among light cells (Figs 28 & 29). The cytoplasm of the dark cells contained abundant mitochondria, large irregular shaped nuclei and scanty rough endoplasmic reticulum (Fig 29). The basal portion of dark cells extended into the elongated processes which interdigitated with neural elements; also numerous desmosomes were found between adjacent dark cells. Langerhans-like cells with tennis racket-shaped granules were seen (Fig 30). The light cells were spherical to cuboidal in shape; their cytoplasm was filled with numerous ribosomes, rough endoplasmic reticulum and mitochondria. The supranuclear region contained membrane bound vesicles. Desmosomes were seen between neighboring light cells, the dark cells processes interlocked with the light cells. Nuclei were spherical to elongated in shape and they were lightly stained (Figs 28, 31 & 32). The apical surface of the cells carried short microvilli (Figs 28 & 32). The basal cells were found near the basal lamina which had a ruffled appearance. J. Vet. Anat. 21

6 Unmyelinated nerve fibers were found in between the basal cells. Synapselike structures were represented at the distal third of the taste buds (Figs 33 & 34). Discussion The African catfish has four pairs of unbranched barbels; one nasal, one maxillary and two mandibular (inner and outer) on the lower jaw. The mandibular barbels were conical in shape with tapered ends. The Corydoras arcuatus type of catfish holds only three pairs of appendages; two large maxillary and a small pair at the chin that showed under a SEM, the condensation of minute risings at surface of barbels (Ovalle and Shinn 1977). The maxillary and outer mandibular barbels showed as minute protuberances in the first-day old larva. All types of barbels appeared in the second-day larva. The 1 st day larva barbels did not have taste buds, while the third-day larva had taste buds that were arranged at the same levels of the surrounding epithelium and possessed few sensory microvilli. The fifth day larva taste buds were concave in shape and were present on the top of the tucked areas. The taste buds in the seventh-day larva appeared as volcano-like elevations. The taste buds in the thirteenth day larva were found on the epidermal papillae and were showing conical elevations. Microvilli coated the tip and the surrounding wall of taste buds and they showed variable diameters. (Mukai et al. (2008) demonstrated that the hatched larvae did not possess taste buds, but it appeared in the first-day stage after the appearance of barbels. The changes in the shape and development of taste buds may be due to the beginning of the exogenous feeding process which starts two days after hatching (Verreth et al., 1992). Larvae of the Clarias gariepinus readily consumed rotifers at the onset of feeding in the hatchling tank after yolk absorption up to the 7th day of feeding. Weaning onto a dry diet takes place gradually from 6 or 7 d after hatch to the end of day 10 (Nyina-Wamwiza et al., 2007). The African catfish larvae and juveniles have the capability to feed in faint light or dark environments indicating that their behavior must be dependent on sensory organs other than the eyes (Appelbaum and Kamler, 2000). Hecht and Appelbaum (1988) carried out behavioral Investigations. Their study showed that feed intake average of larvae with barbels removed was reduced in comparison to the untreated group and the blinded group. In zebra fish maxillary barbels are considered to be a system for studying epithelial mesenchymal development, wound repair, and regenerative cell biology. The J. Vet. Anat. 22

7 maxillary barbel contained a simple cylindrical assemblage of ectodermal, mesodermal and neural crest derivatives, including skin, glands, pigment cells, taste buds, and sensory neurons (Le Clair and Topczewski, 2010). In our work the barbels of the African catfish Clarias gariepinus entail three strata ; an epidermis, a central rod of cartilage and a dermis containing numerous blood vessels, pigment cells, nerve fiber. A similar structure was found in barbels in the Chinese Catfish (Park et al., 2012). We noted numerous flask shaped taste buds scattered among the epidermal cells. Taste buds and club cells in the skin of the barbel have been described in the marine catfish (Kapoor and Bhargava, 1967). In addition, taste buds, mucous cells and club cells have been observed in the barbels of Rita rita (Singh and Kapoor, 1967).Taste buds, mucous cells, and club cells were not detected in the barbels of Mystus vittatus; thus, the barbels were restricted to tactile, and not gustatory, functions (Agarwal and ajbanshi,1965). We observed that the dark and light cells were found in the upper two-third of the taste bud and the basal cells were the third cell type present. In Walking catfish, the taste buds appeared somewhat small and consisted of two long cells which can be distinguished into bright and dark cells (Raji and Norozi,2010), whereas the third type of cell was spindle-shaped with low density in zebra fish (Hansen et al., 2002). Farbman and Yonkers (1971) suggested that the light cells were pickup cells, and so the fluctuations in their potential that in relation to flow pass smooth endoplasmic reticulum lining. We detected membrane-bound vesicles in the supra nuclear region of light cells and desmosomes were seen between adjacent light cells and in the inter digitations between cells at the upper part of taste buds. We also observed fibers of unmyelinated nerves in the area between the lower portions of light cells and the lower third of taste buds. The connections between the membranes of these cells, the existence of the membrane-bound vesicles in the bright cells, and the dense granules in the basal cells provide support for Reutter s (1971) suggestion that the lower third of taste buds gathered taste stimuli from bright cells to translate taste sense into impulses to the responsible sensory nerve. In the barbels of catfish (Parasdurus asotus), light and dark cells of the taste buds had branching processes at their bases, which were in contact with unmyelinated nerve fibers. The base region of light cells was connected with nerve fibers in a configuration resembling a synapse (Changlin and Zuohua, 1981). In addition to chemo-sensibility, J. Vet. Anat. 23

8 taste buds were considered to be multisensory (Hirata, 1966). Desgranges (1978) found that, after nerve transection, the taste buds of the mental barbels of Ictalurus melas remain apparently normal in appearance for up to three weeks, before they disappeared. The sustentacular cells persisted for a longer time than the sensory cells due to differences in taste bud survival time and degeneration. Conclusions The modifications of shape and arrangement of microvilli from larval stage to adult may due to the beginning of the exogenous feeding which started two days after hatching and due to the ability of rearing at the bottom of water and in the dark. The presence of membrane-bound vesicles of light cells, desmosomes found between adjacent light cells, inter digitations between light and dark cells and unmyelinated nerve fibers found in between basal cells and light cells suggest that light cells, dark cells, basal cells and unmylinated nerve fibers act as modifiers in the transmission of taste information from receptor to central nervous system. References Abdel-Hafez, S.M. and El-Caryony, I.A. (2009): An Economic Study on the Production of Catfish In the Egyptian Fisheries: Journal of the Arabian aquaculture society Vol. 4 No 1 June: Agarwal, V.P. and Rajbanshi, V.K. (1965): Morphology and histology of the cutaneous sense organs of Mystus vittatus (BI). Proc Indian Acad Sci 61: Appelbaum, S. and Kamler, E. (2000): Survival, growth, metabolism and behaviour of Clarias gariepinus (Burchell 1822) early stages under different light conditions. Aquacultural Engineering 22: Bancroft, J. D. and Gamble, M. (2008): Theory and practice of histological techniques. Elsevier Health Sciences. Boudriot, F. and Reutter, K. (2001): Ultrastructure of the taste buds in the blind cave fish Astyanax Jordani (Anoptichthys) and the sighted river fish Astyanax mexicanus (Teleostei, Characidae). J. Comp. Neurd., 434: Changlin, L. and Zuohua, S. (1981): Studies on the submicroscopic structure of taste buds in the barbels of the catfish Parasilurus asotus. Acta Zoologica Sinica, 273: Desgranges, J. (1978): Nerves and taste bud degeneration in the catfish Ictalurus melas. Experientia, 34: J. Vet. Anat. 24

9 Elaine, C.J. and George, B.C. (2005): Fine structure of the nasal barbel of the Channel catfish. Ictalurus Punctatu. Journal of Morphology, Vol. 158, Issue 2, Version of Record online: 6 FEB El-Shebly, A.A. (2006): Evaluation of growth performance, production and nutritive value of the African catfish, Clarias gariepinus cultured in earthen ponds. Journal of Aquatic Biology and Fisheries, Vol. 10, No.3: ISSN Farbman, A. and Yonkers, J. (1971): Fine structures of taste buds in the mudpuppy, Necturus maculosus. Amer.J.Anat.131: Fox, H. (1999): Barbels and barbellike tentacular structures in submamalian vertebrates: A Review. J. Hydrobiol., 403: Hansen, A., Reutter, K. and Zeiske, E. (2002): Taste bud development in the Zebrafish, Danio trerio. Developmental Dynamics, 223: Hayat, M. (1986): Basic techniques for transmission Electron Microscope, second ed. Academic press, Baltimore. Hecht, T. and Appelbaum, S. (1988): Observations on intraspecific aggression and sibling cannibalism by larval and juvenile Clarias gariepinus (Clariidae: Pisces) under controlled conditions. Journal of Zoology (London), 214: Hirata, Y. (1966): Fine structure of the terminal buds on the barbels of some fishes Archivum Histologicum Japonicum26: Hossain, M.A., Beveridge, M.C. and Haylor, G.S. (1998): The effects of density, light and shelter on the growth and survival of African catfish (Clarias gariepinus Burchell, 1822) fingerlings. Aquaculture, 160: Ibrahim, N. and El Naggar, G. (2010): Water Quality, Fish Production and Economics of Nile Tilapia, Oreochromis niloticus, and African Catfish, Clarias gariepinus,monoculture and Polycultures. J. World Aquaculture Society. Vol. 41, No 4.: Kapoor, B.G. and Bhargava, S.C. (1967): A study on the barbels of a marine catfish, Arius thalassinus (Rüpp.). Jpn J Ichthyol 14: Le Clair, E.E., & Topczewski, J. (2010): Development and Regeneration of the Zebrafish Maxillary Barbel: A Novel Study System for Vertebrate Tissue Growth and Repair. PLoS one 5(1): e8737. doi: / journal.pone Masson, P. (1929):Trichrome staining and their preliminary technique. J. J. Vet. Anat. 25

10 tech. Meth. and Bull. int. Ass. Med. Mus.: 12,75. Mukai, Y., Tuzan, A. D., Lim, L. S., Wahid, N., Raehanah, S., and Senoo, S. (2008): Development of sensory organs in larvae of African catfish Clarias gariepinus. Journal of Fish Biology, 73(7): Nyina-Wamwiza, L., Wathelet, B. a Kestemont, P. (2007): Potential of local agricultural by-products for the rearing of African catfish Clarias gariepinus in Rwanda: effects on growth, feed utilization and body composition, Aquaculture Research, vol. 38, no. 2, pp , View at Publisher. Ovalle, W.K. and Shinn, S. L. (1977): Surface Morphology of Taste Buds in Catfish Barbels. Cell Tiss. Res. 178: Park, I.S., Seol, D.W., Kim,E, Kim, Y and Lee,Y.D (2006): Histological structure of the barbels of Liobagrus andersoni and L.obesus (Amblycipitidae: Pices) from Korea. J Kor Fish Soc 39: (in Korean). Park, S.; Kim, C. and Choi, J. (2012): Histological Observations and Regeneration of Barbels injuveniles of the Chinese Longsnout Catfish Leiocassislongirostris. Fish Aquat Sci 15(4): Reutter, K. (1971): The taste buds of dwarf catfish Ameiurus nebulosus (Leseur) morphological and histochemical studies. Z.cell researchers, 120, Raji, A.R. and Norozi, E. (2010): Distribution of External Taste Buds in Walking Catfish (Clarias batrachus) and Piranha (Serrasalmus nattereri). J. Appl. Anim. Res. 37 (2010): Richard, R.; Eakin, R.; Eastman, J.T. and Jones, C.D. (2001): Mental barbel variation in pogonophryne scotti Regan. Pisces: Perciformes: Artedidra conidae. Antarctic Science, 13: Singh, C.P. and Bhargava, S. C. (1967): A study on the barbels of a marine catfish, Arius thalassinus (Rüpp.). Jpn J Ichthyol, 14 (4-6), Verreth, J., Els Torreele, Eljallil Spazier, Ad Van der Sluiszen, Jan H. W. M. Rombout, Ronald Booms and Helmut, S. (1992): The Development of a Functional Digestive System in the African Catfish Clarias gariepinus (Burchell). Journal of the World Aquaculture Society Volume 23, Issue 4, pages J. Vet. Anat. 26

11 Fig (1): Photomicrograph of 1-day larva showing (A) the whole larva with yolk sac (YS), encephalic vesicles (EV) and barbels like structures (arrow). x 10, stain (H &E), and (B) Higher magnification of the previous photo showing optic cup (OC), barbels like structures (arrows) and stratified squamous epithelium (ST). (x 100, stain H &E). Fig (2): Scanning electron micrograph of the head of 1-day larva and Fig (3) of 3-day larva showing; yolk sac (ys), maxillary barbel (MB), outer mandibular barbel (OMB), nasal barbell (NB) inner mandibular barbel (IMB), nasal barbel (NB), eye (E), nasal opening (N). Fig (4): Scanning electron micrograph of the enlarged part of the barbel of 3-day larva showing taste buds with sensory microvilli and pores (TB). J. Vet. Anat. 27

12 Fig (5): Light photograph of 5-day larva showing short nasal and tall maxillary barbels (B). (x 40, stain H&E). Fig (6): Higher magnifications of previous photo showing barbels (B), eye (E) cartilage (C) and stratified squamous epithelium (arrow). (x 100, stain H&E). Fig (7): Scanning electron micrograph of head 5-day old larva showing maxillary barbel (MB), outer mandibular barbel (OMB), nasal barbel (NB), inner mandibular barbel (IMB) were folded, teeth (T), nasal opening (N). Fig (8): Scanning electron micrograph of enlarged part of the barbel at 5-day old larva showing concave taste buds with sensory microvilli and pores (P). The microvilli were designed into two manners, condensed aggregation (CMV) mainly at the peripheral while loosely arranged mainly at the center of the taste buds with pores (LMV). J. Vet. Anat. 28

13 Fig (9): Photomicrograph of 13 day old larvae showing barbels (B), smooth muscle (asterisk), gills (G) and eye (E). (x 40, stain H&E). Figs (10,11): Scanning electron micrograph of the head of 7-day and 13-day larvae showing barbels with prominent taste buds (arrow). Fig (12): Scanning electron micrograph of barbels surface of 7-day larva showing folded wavy epithelial surfaces (E), the taste buds alternated a long the barbels, taste buds appeared as volcano like elevations nearly at same heights, with folded wall, roughly framework (arrow). Fig (13): Scanning electron micrograph of barbels surface of 13day old larva showing that the epithelial surfaces were undulant with deep ruts (E). Taste buds placed on the epidermal papillae showing conical elevations of taste bud (arrow) J. Vet. Anat. 29

14 Fig (14): Scanning electron micrograph of the enlarged barbel taste buds of 7-day larva showed volcano like opening (TB) with blunt end and pores and folded surrounding epithelium (E). x Fig (15): Scanning electron micrograph of the enlarged taste buds of 13-day old larvae appeared as conical elevation projecting from the surface epithelium microvilli, coated the tip and surrounding wall of taste buds, there were large diameter microvilli (LMV), small diameter microvilli and pores (P). x Fig (16): Photograph of the head of the adult African catfish showing the types of barbels; one short nasal, one longest maxillary,inner mandibular and outer mandibular barbels at a lower jaw. J. Vet. Anat. 30

15 Fig (17): Photomicrograph of adult fish barbel showing epidermis (ep), dermis (d) and central rod of cartilage (C). (x 10, stain H&E). Fig (18): Photomicrograph of adult fish barbel showing epidermis (ep), dermis (d) and central rod of cartilage (C), nerve fiber (f), RBCS (arrow) and collagen fiber (astrik). (x 25, stain Trichrome). Fig (19): Photomicrograph of the adult fish barbel showing basal cell layer of epidermis (bc), flattened surface cell (arrow), vacuolated cells (v) and dermis (d) (x 40, stain H&E) Fig (20): Photomicrograph of the adult fish barbel showing epidermis (ep), taste buds (t), dermis (d) and pigment cells (arrow). (x 40, stain H&E). J. Vet. Anat. 31

16 Fig (21): Higher magnification of previous photo showing taste buds (t), basal cells with dark nucleus (arrow) and lightly stained columnar cells(asterisk).( x 100,stain H&E). Fig (22): photomicrograph of supporting cartilage showing cartilaginous cell (cc) and nucleus (arrow). (x 100, stain H&E) Fig (23): Scanning electron micrograph showing epithelial surface of barbel of adult African catfish characterized by circular whirlpools, where epidermal projection (EP) arranged peripherally. At the center of whirlpool was taste buds which were polyhedral semi-circular forms or oval shapes. Taste buds had special character like (concave disks) or Mulberry form (TB). Groove surrounded the taste buds (G). (x 2000). The concave apex had central pore and microvilli Fig (24): Epithelial surface showing epidermal projections, deep farrows (F) between projections. It had two pits for mucous secretion (P).The projection is covered by rough epithelial Bristles giving it a Velvety appearance(es). x J. Vet. Anat. 32

17 Fig (25): Higher magnifications of previous photo showing central pore and microvilli (arrow) of concave disk-like taste bud (t) and epidermal cells (ep). (x 5000). Fig (26): Another scanning electron microscope depicting microvilli appeared at the lateral aspect of the Mulberry form taste buds (arrow). (x 5000). Fig (27): Transmission electron micrograph of taste buds showing dark cells (DC), light cells (LC) and basal cells (BC). (x 500) J. Vet. Anat. 33

18 Fig (28): Electron micrograph of dark cell (DC) of taste bud found between 2 light cell (LC) showing microvilli of dark cell (arrow head), process of dark cell (arrow). (x 5000). Fig (29): Another electron micrograph of dark cell depicting numerous mitochondria (m), few r ER rough endoplasmic reticulum (r) and large irregular shape nuclei (N). (x 6000). J. Vet. Anat. 34

19 Fig (30): Electron micrograph of basal portion of dark cells (DC) showing numerous desmosomes (S), neural elements (arrow), Langerhans like cells (G) and nucleus (N). x Fig (31): transmission electron micrograph of light cells showing numerous ribosomes (i), rough endoplasmic reticulum (r), mitochondria (m) and nucleus (N). x Fig (32): Another electron micrograph of light cell depicting short microvilli (arrow head), desmosomes (S), mitochondria (m), rough endoplasmic reticulum(r), ribosomes (i), membrane bound vesicles (arrow) and nucleus with clear nucleolus (u). x J. Vet. Anat. 35

20 Fig (33): Transmission electron micrograph of basal cells (bc) showing ruffled basal lamina (bl) Unmyelinated nerve fiber (arrow), synapse like structure (y) and nucleus of basal cells (N). x Fig (34): Another electron micrograph of basal cells (bc) showing desmosomes (S) unmyelinated nerve fiber (f), and electron dense granules(arrow). x 3000 Author address: Faculty of Veterinary Medicine, Alexandria University, Edfina-Rashid-Behera.Egypt. am_derbalah@hotmail.com. J. Vet. Anat. 36