The present work was carried out on 40 specimens of oesophaguses of both sexes of catfish (carnivorous fish) and grass carp (herbivorous fish) in order to observe the morphological and histological differences between the two species. Oesophagus of catfish was divided into 2 parts: anterior and posterior ones. The anterior part of the oesophagus of catfish was characterized by the presence of numerous mucosal folds. It was lined by stratified epithelium with goblet cells. In addition to club cells were observed in between the stratified epithelium. Scanning electron examination of the oesophageal epithelium of catfish demonstrated the presence of microvilli and fingerprint-like microridges in the superficial cell layer. The posterior part of the oesophagus of catfish was characterized by simple columnar mucus-secreting epithelium. The oesophagus of grass carp had shown the same structure along its entire length. It consisted of less folded mucosa than that observed in the oesophagus of catfish. The epithelium was characterized by the presence of taste buds. In conclusion, the present work revealed some differences in the structure of catfish oesophagus and grass carp oesophagus. These differences are related to type of food and feeding habits of each species.
Nile catfish (
The aim of the present study is to describe and compare the anatomical and histological structures of the oesophagus of the catfish as an example of carnivorous fish and the grass carp as an example of herbivorous fish, using light and electron microscopy. This may provide a comparative basis for future studies of the feeding patterns of both species as well as a contribution to the development of fish farming.
The materials employed in this study consisted of randomly obtained 20 adult specimens of both sexes of the catfish
The oesophagus was dissected immediately and then put on a filter paper, and the length (cm) and diameter (cm) were measured using a caliber.
For histological studies, the samples were dissected as soon as possible from the anterior and posterior parts of the oesophagus of both species at
For scanning electron microscopy, formaldehyde-fixed specimens of oesophagus of both species were washed in 0.1 M cacodylate buffer for 1 h and then transferred to a 1% solution of tannic acid for 2 h at room temperature. The pieces then were washed again in buffer and postfixed for 2 h in 1% osmium tetroxide. The postfixed materials were washed and dehydrated in a series of increasingly concentrated solutions. They were then mounted on aluminum stubs and sputter-coated with gold/palladium for 3 min. The specimens were examined with a JEOL. JSM-5400 LV scanning electron microscope.
For transmission electron microscopy, small pieces 2-3 mm long from the different portions of anterior part of oesophagus of catfish were fixed and dehydrated as in semithin. Ultrathin sections obtained by a Reichert ultramicrotome were stained with uranyl acetate and lead citrate (Reynolds, 1963) and examined with a JEOL. JEM-100 electron microscope.
Morphometrical measurements were performed by using Image analysis system (Leica Q500MC). Measurements include diameter of the oesophagus, thickness of the wall, mucosa, submucosa and tunica muscularis, diameter of the lumen, number of mucosal folds/cross section, height and width of the mucosal folds, and height of the surface epithelium.
The catfish had a slender blackish-coloured body without scales and a flat bony head, which took an eel-like appearance. The mouth was large terminal in position with four pairs of barbels (Figure
Showed statistical analysis of various measurements of catfish and grass carp.
Measurements | Catfish | Grass carp |
---|---|---|
Body weight (gm) |
|
|
Total length of fish (cm) |
|
|
Standard length of fish (cm) |
|
|
Length of oesophagus (cm) |
|
|
Diameter of oesophagus (cm) |
|
|
The values were represented by mean
Photomicrographs of catfish and grass carp and their anatomical features of their oesophagi. (a) Dorsolateral view of catfish. (b) Photograph of the gastrointestinal tract of catfish, showing their oesophagus (O), stomach (S), which is overlapped by liver (L) and connected to intestine (I) caudally. (c) Lateral view of grass carp. (d) Photograph of the gastrointestinal tract of grass carp showing their oesophagus (O) connected to the intestinal bulb (IB). g: gall bladder. Bars: (a) 0.75 cm; (b) 1.5 cm; (c) 0.67 cm; (d) 0.80 cm.
The oesophagus of catfish run from the posterior end of the pharynx anteriorly to the anterior part of cardiac region of the stomach caudally; being ventrally overlapped by the liver, its anterior region was wide and funnel-shaped and its posterior region was tubular in shape (Figure
The oesophagus of grass carp run from the posterior end of the pharynx anteriorly to the intestinal bulb caudally, being ventrally overlapped by the liver and its shape was cylindrical and straight along its entire length (Figure
The oesophagus of catfish was divided into 2 parts; anterior and posterior parts based on type and thickness of the epithelium and tunica muscularis.
The mean diameter of the anterior part of oesophagus was
Measurements of oesophagus of both fish species and their relation (%) to the wall measurements.
Grass carp | Catfish | Measurements | |
---|---|---|---|
Oesophagus | Posterior part of oesophagus | Anterior part of oesophagus | |
|
|
|
Diameter of the organ (µm) |
|
|
|
Thickness of the wall (µm) |
|
|
|
Diameter of the lumen (µm) |
|
|
|
Thickness of the mucosa (µm) |
|
|
|
Number of mucosal folds/cross section |
|
|
|
Height of mucosal folds (µm) |
|
|
|
Width of mucosal folds (µm) |
|
|
|
Height of the epithelium (µm) |
|
|
|
Thickness of submucosa (µm) |
|
|
|
Thickness of muscularis (µm) |
The values were represented by mean ± standard error.
The mean thickness of the tunica mucosa was
Photomicrograph showed the morphological characteristic features of the anterior part of oesophagus of catfish (a–e), posterior part of oesophagus of catFish (f–i), and oesophagus of grass carp (j–n). Highly folded mucosa (m); short mucosal folds (mf); wide channels of lumen (L); columnar epithelium (ep); goblet cells (gc); taste buds (Tb); club cells (cc). Notice the negative PAS reaction of club cells (cc), muscularis mucosa (mm), lamina propria (Lp), tunica submucosa (S), tunica muscularis (M), and adventitia (ad). The square indicated one mucosal fold. (a), (e), (i), (f), (j), and (n)
Transmission electron micrograph of the club cells of the anterior part of oesophagus of catfish showing 2 nuclei (N), many vesicles (V), moderate dense secretory materials (s), and mitochondria (M) (
Semithin sections showed that the mucosal epithelial cells were stratified in type and their superficial cells bore microridges, in addition to presence of toluidine blue-positive goblet cells. The goblet cells appeared spherical or oval in form and lacked the basal narrow part that was found usually at the base of these cells. The club cells appeared as giant polyhedral cells with pale staining cytoplasm. They were mononucleated or binucleated cells, where the two nuclei were situated very close to each other. Undifferentiated or basal cells were located at the base of the epithelium (Figure
Semithin section of the stratified mucosal epithelium of the anterior part of oesophagus of catfish (a) showing the apical microridges (arrowheads), club cells (cc), goblet cells (gc), and basal cells (bc). In the posterior part of oesophagus of catfish (b), positive toluidine blue reaction was observed in apical epithelial cells (ep). Basal cells (arrow). (c) Oesophagus of grass carp showing microridges (arrowheads), metachromatic reaction of goblet cells (gc), and taste bud (Tb). Connective tissue lamina propria (Lp). (Toluidine blue,
Scanning electron microscopic observations of the mucosa of the anterior part of the oesophagus showed numerous primary, secondary, and tertiary longitudinal folds (Figure
Scanning electron micrograph of the anterior part (a–c) and posterior part (d–f) of oesophagus of catfish and oesophagus of grass carp (g–i). Polyhedral-shaped superficial epithelial cells (ep). Mucosal folds (mf), microvilli (mv), microridges (mr), and long concavities (c) between them. Notice the presence of goblet cells (gc), microvilli (arrow), microridges (arrow head), and mucus (m).
The mean thickness of the tunica submucosa was
The mean diameter of the posterior part of oesophagus of catfish was
As in the anterior part of the oesophagus, the wall of the posterior part was formed of 4 distinct layers: tunica mucosa, tunica submucosa, tunica muscularis, and tunica adventitia.
Tunica mucosa was a thin layer; its mean thickness was
Semithin sections showed that the mucosal epithelium of the posterior part consisted of tall columnar cells with middle oval light nucleus that contained distinct nucleoli. The apical part of these cells contained mucous granules, which reacted positively to toluidine blue. Some basal dark cells of irregular shape were present in the basal part of the epithelium (Figure
Scanning electron microscopic observations of the mucosa of the posterior part of oesophagus showed simple longitudinal folds (Figure
Muscularis mucosa consisted of bundles of smooth muscle fibers, surrounded by numerous collagenous fibers (Figure
The mean thickness of the tunica submucosa was
The posterior part of the oesophagus had thicker muscularis than the anterior part, and it was composed of inner circular and outer longitudinal smooth muscle fibers that were held by connective tissue fibers (Figure
The tunica adventitia was formed of loose connective tissue that contained collagenous fibers and small blood vessels (Figure
The oesophagus of grass carp was of the same structure and appearance along their entire length. Its mean diameter was
The mean thickness of the tunica mucosa was
Semithin sections showed microridges in the apical part of the superficial epithelial cells of the oesophagus of grass carp. Undifferentiated basal cells were located at the base of the epithelium. Goblet cells were not found typically at the surface but usually were lain deeply and characterized by a metachromatic reaction to toluidine blue. Taste buds appeared as fusiform structure of pale cells with prominent taste pore (Figure
Scanning electron microscope observation of the oesophageal mucosa revealed numerous folds that left distinct long concavities in between them (Figure
The tunica submucosa was formed of dense irregular connective tissue that contained collagenous fibers and numerous striated longitudinal muscle bundles that were sparsely distributed (Figure
The mean thickness of the tunica muscularis was
The present work was carried out on 40 specimens of both sexes of catfish (carnivorous fish) and grass carp (herbivorous fish) in order to observe the morphological and histological differences between the two species. The results of the present work revealed some differences in the structure of the oesophagus of both species related to type of food and feeding habits of both species. The gastrointestinal tracts of fish show remarkable differences in function and structure, these differences were related to type of food, feeding habits, body weight, shape, and sex [
The present study revealed that the oesophagus of catfish was divided into anterior and posterior parts. The differentiation of oesophagus into two morphologically distinct zones, based on type and thickness of the epithelium and tunica muscularis has been documented in many fishes such as garfish [
The current observations revealed that the anterior part of the oesophagus of catfish was characterized by the presence of numerous mucosal folds that may allow maximal distension for prey and broken down food, and it was lined by stratified epithelium with goblet cells. The epithelium of the anterior part of the oesophagus of carnivorous fish acted as a constitutive adaptation that protected the oesophagus against live prey damages [
Our results revealed that the oesophagus of both species possessed a high density of goblet cells as compared with other sections of the gastrointestinal tract. The increased number of goblet cells in the oesophagus of all fish species in general was probably due to the absence of salivary glands, as the mucin excreted in the oesophagus and buccal cavity compensates the absence of salivary glands in fish [
The present study revealed the presence of club cells in the anterior part of the oesophagus of catfish, which appeared as large acidophilic cells in between the lining stratified epithelium. The transmission electron microscopic observations revealed that the cytoplasm of the club cells contained rER, free ribosomes, mitochondria, and many vesicles, which contained electron dense secretory material. Several names have been given to club cells such as “clavate,” “giant,” and “alarm substance cells” [
The basal part of the epithelium of the oesophagus of catfish contained undifferentiated cells. These cells undergo cytoplasmic changes and eventually become epithelial cells or goblet cells and also the club cells arise from it [
The present study demonstrated the presence of taste buds in the oesophagus of grass carp, indicating that the fishes select the type of food intake by either food rejecting or swallowing. The taste buds acted as chemoreceptors for specific selection of food before swallowing [
Scanning electron microscopic examination of the oesophageal epithelium of catfish demonstrated the presence of microvilli in the superficial cell layer. The presence of these prominent microvilli indicates an adaptation to rapid ion absorption [
Histological examination of the oesophagus of grass carp and catfish also revealed that the presence of numerous elastic fibers in the lamina propria and submucosa (data not shown) increases elasticity for swallowing large items of foods. In addition, the extensive core of lamina propria in the mucosal folds of oesophagus of catfish was probably to maintain the integrity of the wall and prevent rupture of the mucosal lining as it is to be stretched around the prey during the act of swallowing [
Our results also revealed the presence of bundles of striated longitudinal muscles in the oesophageal submucosa. Otherwise, these striated muscles might be important for catfish to reject any unpalatable food and provide reinforcement to the oesophagus, which is subjected to violent extensions by ingestion of food. However, these muscles in submucosa of grass carp might be related to the coordination of the contraction of the oesophagus with movements of the pharyngeal teeth to allow expansion of the oesophagus for the ingestion of foods.
The thickness of the tunica muscularis particularly in the posterior part of the oesophagus of catfish might represent a powerful tool to strengthen the oesophageal wall, protect it from engorged bulky food, facilitate regurgitation, and also act as a triturating device for solid ingested materials [