World Applied Sciences Journal 12 (8): 1133-138, 2011 ISSN 1818-4952 © IDOSI Publications, 2011
Comparative Scanning Electron Microscope Study of the Buccal Cavity in Juvenile and Adult Sea Bass (Dicentrachus labrax) N.E.R. El-Bakary Department of Zoology, Faculty of Science, Mansoura University, New Damietta, Egypt Abstract: The buccal cavity is the entrance of nutrients into juvenile and adult fish body and its therefore important to know the surface architecture of it in both stages of sea bass in order to insure a continuity of the species. The buccal cavity of both stages were examined with scanning electron microscopy. The roof and the floor of the mouth cavity of juvenile was characterized by the presence of long, conical shaped, papilliform teeth which was pointed inward and arranged in four rows while that of the adult characterized by several rows of papilliform teeth and several epithelial protrusions. The dorsal lingual region of juvenile appeared smooth than that of the adult which was characterized by the presence of papilliform teeth. Each epithelial cell was characterized by the presence of a series of microridges. The microridges of the lingual epithelium of juvenile were smooth, uniform in width, sinous and not sinuous while that of the adult were rough and sinous. Mucous cell openings and the taste pores of the taste buds were found numerous in the dorsal lingual epithelium of the adults than those of juvenile tongues. The buccal cavity shows significant modifications in relation to food and feeding ecology of the fish. Information gathered may help in formulating diets needed for optimum growth of fishes. Key words: Buccal cavity %Fish % Juvenile % Adult % Scanning electron microscope INTRODUCTION The buccal cavity is the entrance of nutrients into the larval and adult fish body and its therefore important to understand the functions and limitations in processing capacity during early life stages. Fish larvae are characterized by digestive systems and diets that differ from adults. Larvae undergo a pattern of trophic ontogeny, changing diet with increasing size and these changes result in differences in digestive requirements. At first feeding, the larval alimentary canal is functional, but is structurally and functionally less complex than that of adults [1]. Few scanning electron microscope studies were done on the buccal cavity and feeding habits of the juveniles if compared with that of the adults plankton feeder, Catla catla [2] and on carnivorous fish species, Gadus morhua [3]. The secretory epithelium in the buccal cavity of the carnivorous cichlid Oreochromis alcalicus grahami using scanning and transmission electron microscopy was observed [4]. Large interspecific differences regarding the morphology, presence of teeth and structure of the mucosa in the oral cavity of teleosts were reported [5, 6].
Thus descriptions available for one species do not necessarily hold for another. There are generally two stages to feeding in teleost fishes, prey capture and processing. The prey may be separated from unwanted material, such as sand or other debris, by winnowing behaviors, or a protective armor may be cracked to access the flesh of the prey, as in the case of molluscivore. During these processing behaviors teleost fishes usually employ a second set of jaws, the pharyngeal jaw apparatus. There are broad methods of prey capture in fishes: i) filter feeding, whereas the prey is filtered from the water using a variety of retention mechanisms. ii) biting where the teeth of the oral jaws are applied to the prey.iii)ram feeding whereas the prey is overtaken and engulfed in an open mouth. iv) suction feeding where the prey is sucked into the mouth by a stationary predator. Suction feeding is belived to be the primary method of prey capture in teleost fishes [7]. It is the most common method of prey capture in predators of mobile animal prey. The aim of the present study was to provide a basis for better knowledge of the surface architecture of the mouth cavity of juvenile and adult Dicentrachus labrax
Corresponding Author: N.E.R. El-Bakary, Department of Zoology, Faculty of Science, Mansoura University, New Damietta, Egypt, E-mail:
[email protected].
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in relation to its feeding habits. It is mostly a night hunter, feeding on small fish, polychaetes, cephalopods and crustaceans. The basic knowledge about the buccal cavity of early life stage will provide insight into how the fish adapt to their environment and survive.
RESULTS
MATERIALS AND METHODS The roof and floor of the mouth cavity of juvenile and adult Dicentrachus labrax which were collected from the Mediterranean Sea near Damietta-Egypt were treated and prepared for scanning electron microscopy. They were fixed in 10% formalin, post fixed with 1% osmium tetroxide in 0.1M sodium cacodylate buffer at pH 7.2 for 1h at 4°C. Thereafter, the specimens were dehydrated through graded series of ethanol and critical point dried. They attached to aluminium stubs facing upwards, covered with carbon tabs and then were, sputtered with gold and then examined with a scanning electron microscope (JSM. 5300) at an accelerating voltage of 15kV.
The buccal cavity is not equal in length and width in both larval and adult stages. The oral aperture is wide. Both jaws are armed with a patch of several irregular rows of papilliform teeth curving inwards. Anatomically, the roof of the buccal cavity consisted of premaxilla, maxilla, velum, palatine bones and palate while the floor consisted of dentaries, angulars, velum and tongue. On the floor of the buccal cavity is a muscular prominence comparable to the tongue of higher vertebrates. Roof of the Mouth Cavity of Juvenile and Adult: In juveniles, the papilliform teeth were long, conical shaped, pointed inward and arranged in four rows (Fig. 1a,b). There are several epithelial protrusions in the upper jaw and the epithelium of the roof are coated with many mucous secretions (Fig.1c,d). The papilliform teeth pierced through the epithelium, thus the distal part of
Fig. 1: Scanning elctron micrograph of the surface architeccture of the roof of the mouth cavity of Dicentrachus labrax (juvenile) a) UJ: upper jaw; P: palatine; PR: palatine regions; arrow: molarifirm teeth in PR. b) papilliform teeth in the palatine regions (PR).c) arrow indicates epithelium of the roof.e) m: mucus secretions. Arrow indicates microridges in the epithelium of the papilliform teeth.f) papilliform teeth (black star) in the parasphenoid region.
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Fig. 2: Scanning electron micrograph of the surface architecture of the roof of the mouth cavity of adult Dicentrachus labrax. A,b) several rows of papilliform (black star) and molariform (white star) teeth.c) serveral epithelial protrusions are found between papilliform teeth which directed backward.
Fig. 3: Scanning electron micrograph of the floor of mouth cavity of juvenile (a,b) and adult (c,d) Dicentrchus labrax. LJ, llower jaw; white head arrow, papilliform teeth; black head arrow, papilliform teeth directed backward; black star, a depression in the middle of the floor; white star; molariform teeth.
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Fig. 4: Scanning electron micrograph of the dorsal lingual epithelium of juvenile (a,b) and adult (c-e) Dicentrachus labrax (a,b) m: mucus secretions, arrow:microridges, arrow head: taste pores. c) arrow: papilliform teeth, white star: epithelial protrusions. d) arrow: taste pores on epithelial protrusions.e) epithelial cells with distinct boundaries and compactly arranged microridges. each teeth was exposed (Fig.1e,f). The tooth tips appeared fragile and often show wear and breakages. The proximal part of each tooth remained covered under the epithelium (Fig.1e,). In adults, several rows of papilliform teeth are arranged and pointed inward and between them are found several epithelial protrusions (Fig.2a-c). Floor of the Mouth Cavity of Juvenile and Adult: The teeth has the the same appearance like that of the upper jaw in both stages. The floor of the mouth cavity is distinguished by a space in the middle of it. It was clear in the adult than juvenile stage (Fig.3a-d).
lingual epithelium of juvenile (Dicentrachus Labrax) were smooth uniform in width, sinous and not sinuous (Fig 4b) while that of the adult were rough and sinous (Fig. 4d,e). The microridges were compactly arranged in juvenile but those of the adult were more compact and extensively branched. Mucous cell openings and the taste pores of the taste buds were found numerous in the dorsal lingual epithelium of the adults (Fig.4d,e) than those of juvenile (Dicentrachus Labrax) tongues. DISCUSSION
The Dorsal Lingual Surface of Juvenile and Adult: The dorsal lingual region of juvenile appeared smooth (Fig.4a) than that of the adult (Fig. 4c) which was characterized by the presence of molariform and papilliform teeth. Epithelium of the tongue of juvenile and adult Dicentrachus labrax consisted of a mosaic irregular polygonal epithelial cells of varied dimensions (Figs. 4b,d,e). Each epithelial cell was characterized by the presence of a series of microridges. The microridges of the
Differences in the dentition, epithelial protrusions and microridges of the dorsal lingual surface of juvenile and adult sea bass (Dicentrachus Labrax) could be taken as an adaptations to the food types and the food preference of these stages. Fishes can have teeth on jaws, the tongue, the roof of the mouth and the pharynx. Some fishes may have a combination of kinds of teeth; for example, in many sharks, the teeth in the upper and lower jaws can be quite different and the teeth at the front of the jaw may differ from those at the sides in shape and, especially, in size.
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The teeth of juvenile and adult Dicentrachus labrax are papiliform and are arranged in masses. The presence of teeth on jaws is required to hold or grasp and to prevent the escape of small prey but to tear the food in the buccal cavity may not be of much significance. In fishes, the tongue is a primary tongue that is not muscular and is used mainly for channeling water. The tongue contributes to feeding behavior by either conducting water through the mouth (as is the case in fishes) or by actively manipulating the prey within the mouth. For some species, such as lampreys and other parasitic fishes, the tongue has bony plates that act like teeth for rasping and obtaining a blood meal [8]. The tongue of adult Dicentrachus labrax was characterized by papilliform teeth which help in the manipulation of the prey before reaching pharyngeal teeth to complete the process while the tongue of juvenile characterized by the absence of teeth. The free surface of the epithelial cells at the mouth cavity of different fishes, is characteristically differentiated into series of microridges and referred to as cytoplasmic folds, microvilli, microfolds, ridges or microridges [9]. Cells bearing microridges are commonly associated with mucus secreting epithelia. The functional significance of microridges has been considered to be related in some way to the function of mucus. Mucous coats are frequently considered to serve as a lubricant, facilitating movement of material over a cell surface and protecting the plasma lemma from damage by abrasion [10]. Microridges on the epithelial surface of the buccal cavity of both juvenile and adult stage help in lubrication of the prey. Compactly sinous microridges in the buccal cavity of the adult Dicentrachus labrax secrete more mucus than juvenile because the prey needs more lubrication and protect plasma lemma from abrasion by hard structure of the prey and possible mechanical injury. This protective function requires that an unbroken layer of mucus covers the tissue surface. In tissues where goblet cells are interspersed among non mucus secreting cells the microridges offer a course of channels for the spread of mucus away from secretory cells on to neighboring cell surfaces. Mechanical deformation of mucus–secreting epithelia, such as stretching or direct pressure, causes goblet cells to secrete mucus. Mucus appears initially as patches on the surface. Microridge define channels into which the mucus can flow. This dispersal is augmented by the pressure of an object advancing along the surface; the greater the force on the surface, the greater the amount of the mucus secreted and this explain the appearance of
many mucous glands opening in the lingual surface of the adult. The form of microridges corresponds to type and rate of secretion at the cell apex. Some variations in surface pattern may reflect the stage of maturation of a particular cell, or groups of cells that have recently reached the surface. Furthermore, the development of microridges are then a consequence of the arrival of new membranes, as vesicles carrying the secretion fuse with the apical plasmalemma and high ridges would indicate a rapid sequence of arrival of secretory vesicles at the surface [6, 10, 11, 12]. Compactly arranged microridges of adult Dicentrachus labrax often interconnected with microbridges, may also be considered to provide rigidity to the free surface of the epithelium, in order to protect against physical abrasions, when manoeuvring of ingested prey. Fish farming workers must take in consideration the nature of food for juvenile must fit with the nature of the oral cavity. The informations gathered about the the feeding habits of juvenile should be studied further and may help in formulating diet and improve their survival as one of the major proplem in fish culture is the high mortality during the initial stages of larval development. REFERENCES 1.
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