Morphology of the Digestive Tract of the African Catfish (Clarias gariepinus Burchell, 1822)

Abstract

Seventy five African catfish made up of 25 fingerlings, 25 juveniles and 25 adults, sourced from Yuep Farms, Umuahia, Abia State of Nigeria, were used for the study. The fish were weighed, and the standard and total body lengths were measured. The fingerlings and juveniles were euthanized with chloroform, while the adults were humanely immobilized by stunning. The digestive tracts were dissected out and the intestinal lengths were measured. The relative intestinal lengths were also determined. Slices of oropharyngeal wall, tongue, oesophagus, stomach, intestine, rectum and anus were excised and fixed in 10% neutral buffered formalin, for 16-24 hours. They were embedded in paraffin wax, sectioned and stained with haematoxylin and eosin. Adult pharyngeal pad was sliced into small pieces, decalcified and similarly processed. The carbohydrate histochemistry was carried out using periodic acid Schiff (PAS), alcian blue (AB) at pH 2.5, and a combination of AB and PAS procedures. Sections were examined with a light microscope and photographed with a Moticam camera fixed to the microscope. Data were analysed statistically using analysis of variance. Duncan’s multiple range test was used to separate variant means, and significance was accepted at p< 0.05. Grossly, the oral surfaces of the palatine and mandibular rostral ends of the fish contained roughened grinding plates, with a degree of roughness that increased with age. The tongue was attached to the floor of the oro-pharyngeal cavity. Pharyngeal pads were absent in the fingerlings, rudimentary in the juveniles and well developed in the adults. The oesophagus connected the oropharyngeal cavity to the stomach. The stomach was J-shaped with a Seventy five African catfish made up of 25 fingerlings, 25 juveniles and 25 adults, sourced from Yuep Farms, Umuahia, Abia State of Nigeria, were used for the study. The fish were weighed, and the standard and total body lengths were measured. The fingerlings and juveniles were euthanized with chloroform, while the adults were humanely immobilized by stunning. The digestive tracts were dissected out and the intestinal lengths were measured. The relative intestinal lengths were also determined. Slices of oropharyngeal wall, tongue, oesophagus, stomach, intestine, rectum and anus were excised and fixed in 10% neutral buffered formalin, for 16-24 hours. They were embedded in paraffin wax, sectioned and stained with haematoxylin and eosin. Adult pharyngeal pad was sliced into small pieces, decalcified and similarly processed. The carbohydrate histochemistry was carried out using periodic acid Schiff (PAS), alcian blue (AB) at pH 2.5, and a combination of AB and PAS procedures. Sections were examined with a light microscope and photographed with a Moticam camera fixed to the microscope. Data were analysed statistically using analysis of variance. Duncan’s multiple range test was used to separate variant means, and significance was accepted at p< 0.05. Grossly, the oral surfaces of the palatine and mandibular rostral ends of the fish contained roughened grinding plates, with a degree of roughness that increased with age. The tongue was attached to the floor of the oro-pharyngeal cavity. Pharyngeal pads were absent in the prominent constrictiSeventy five African catfish made up of 25 fingerlings, 25 juveniles and 25 adults, sourced from Yuep Farms, Umuahia, Abia State of Nigeria, were used for the study. The fish were weighed, and the standard and total body lengths were measured. The fingerlings and juveniles were euthanized with chloroform, while the adults were humanely immobilized by stunning. The digestive tracts were dissected out and the intestinal lengths were measured. The relative intestinal lengths were also determined. Slices of oropharyngeal wall, tongue, oesophagus, stomach, intestine, rectum and anus were excised and fixed in 10% neutral buffered formalin, for 16-24 hours. They were embedded in paraffin wax, sectioned and stained with haematoxylin and eosin. Adult pharyngeal pad was sliced into small pieces, decalcified and similarly processed. The carbohydrate histochemistry was carried out using periodic acid Schiff (PAS), alcian blue (AB) at pH 2.5, and a combination of AB and PAS procedures. Sections were examined with a light microscope and photographed with a Moticam camera fixed to the microscope. Data were analysed statistically using analysis of variance. Duncan’s multiple range test was used to separate variant means, and significance was accepted at p< 0.05. Grossly, the oral surfaces of the palatine and mandibular rostral ends of the fish contained roughened grinding plates, with a degree of roughness that increased with age. The tongue was attached to the floor of the oro-pharyngeal cavity. Pharyngeal pads were absent in the on separating it from the intestine. The proximal intestinal wall was thick and continuous with coiled middle and distal parts of the intestine in all groups. The relative intestinal length of the juveniles (1.28 ± 0.06) was significantly higher (p<0.05) than that of the fingerlings (0.87 ± 0.07) and adults (0.78 ± 0.04). Histologically, the tunica mucosa of oro-pharynx, tongue, pharyngeal pad and oesophagus were lined by stratified mucous epithelium in all age groups. Taste buds were observed in the adult oro-pharyngeal mucosa. The adult pharyngeal pad contained teeth, mucous cells and taste buds in the stratified epithelium. The adult and juvenile oro-pharyngeal and oesophageal epithelium contained eosinophilic club cells. Lamina propria of the oro-pharynx contained dense collagen connective tissue in the adult. Muscularis mucosa was absent in all groups. The oesophageal tunica muscularis was composed of skeletal muscle fibres arranged in an inner longitudinal and outer circular layers in juveniles. In the adult oesophagus, the circularly oriented muscle fibres predominated and were interspersed with bundles of longitudinal muscle fibres. An intermediate region between the adult oesophagus and stomach (oesogaster) was characterized by presence of stratified mucous epithelium and gastric gland within the lamina propria. The entire stomach surface was covered by simple columnar mucous epithelium at the base of which were intraepithelial leukocytes. In all age groups, the cardiac and fundic regions of the stomach contained glands in the lamina propria while the pyloric region lacked these glands. The pyloric sphincter was comprised of thickened circular smooth muscle coat in all age groups. The proximal intestine in all ages presented complex labyrinthine mucosal folds, the luminal parts of which bore villar extensions. The middle and distal intestinal mucosa presented simple finger-like mucosal folds in all age groups. The intestinal epithelium in all groups comprised of simple absorptive columnar cells with brush border, intraepithelial leukocytes and goblet cells. The tunica muscularis contained a myenteric plexus in all groups. Carbohydrate histochemistry in all ages under study revealed positive reaction to PAS in the oesophageal mucous cells, stomach simple columnar epithelium and intestinal goblet cells. At pH 2.5, the oesophageal mucous cells and intestinal goblet cells were positive to AB reaction but the stomach epithelium was AB negative in all groups. On subjecting the mucin containing entities to combined AB and PAS reaction after diastase pre-treatment, the oesophageal and oro-pharyngeal wall mucosa presented mixed acid and neutral mucins in all the age groups. The stomach presented only neutral mucins while the intestine presented mixed mucin with acid mucin dominating in the adult proximal intestine. The presence of stratified mucous epithelium observed in the oro-pharyngeal wall and oesophagus is for protection of the tract from abrasion from rough feed. The mucin in the oesophagus is also associated with pregastric digestion of food since the teleost digestive tract lacks salivary glands. The eosinophilic club cell is for non-specific immunity. The taste buds seen in the adult group is for selection and rejection of food materials by gustation. The oesogaster seen in the adult group suggests a structure involved in increasing surface area for gastric digestion and production of extra mucin to reduce the effect of acidic gastric content. The glands in the stomach lamina propria contain oxyntopeptic cells that produce both hydrochloric acid and pepsinogen. The absence of gastric glands in the pyloric region may be an adaptation to reduce the quantity of gastric acid that enters the proximal intestine that needs an alkaline medium for maximal activity of pancreatic enzymes. The reticulated labyrinthine mucosal folds in the proximal intestine increases surface area for feed digestion and absorption. The increasing number of goblet cells towards the rectum is for increased mucin production to reduce abrasion from fecal materials. The acid mucin seen is associated with protection against mechanical injury from food fibres and pathogenic agents while the neutral mucin is involved in pre-gastric digestion in the oesophagus, buffering the effect of gastric acid in the stomach and transport of small molecules in the intestine. Seventy five African catfish made up of 25 fingerlings, 25 juveniles and 25 adults, sourced from Yuep Farms, Umuahia, Abia State of Nigeria, were used for the study. The fish were weighed, and the standard and total body lengths were measured. The fingerlings and juveniles were euthanized with chloroform, while the adults were humanely immobilized by stunning. The digestive tracts were dissected out and the intestinal lengths were measured. The relative intestinal lengths were also determined. Slices of oropharyngeal wall, tongue, oesophagus, stomach, intestine, rectum and anus were excised and fixed in 10% neutral buffered formalin, for 16-24 hours. They were embedded in paraffin wax, sectioned and stained with haematoxylin and eosin. Adult pharyngeal pad was sliced into small pieces, decalcified and similarly processed. The carbohydrate histochemistry was carried out using periodic acid Schiff (PAS), alcian blue (AB) at pH 2.5, and a combination of AB and PAS procedures. Sections were examined with a light microscope and photographed with a Moticam camera fixed to the microscope. Data were analysed statistically using analysis of variance. Duncan’s multiple range test was used to separate variant means, and significance was accepted at p< 0.05. Grossly, the oral surfaces of the palatine and mandibular rostral ends of the fish contained roughened grinding plates, with a degree of roughness that increased with age. The tongue was attached to the floor of the oro-pharyngeal cavity. Pharyngeal pads were absent in the fingerlings, rudimentary in the juveniles and well developed in the adults. The oesophagus connected the oropharyngeal cavity to the stomach. The stomach was J-shaped with a prominent constriction separating it from the intestine. The proximal intestinal wall was thick and continuous with coiled middle and distal parts of the intestine in all groups. The relative intestinal length of the juveniles (1.28 ± 0.06) was significantly higher (p<0.05) than that of the fingerlings (0.87 ± 0.07) and adults (0.78 ± 0.04). Histologically, the tunica mucosa of oro-pharynx, tongue, pharyngeal pad and oesophagus were lined by stratified mucous epithelium in all age groups. Taste buds were observed in the adult oro-pharyngeal mucosa. The adult pharyngeal pad contained teeth, mucous cells and taste buds in the stratified epithelium. The adult and juvenile oro-pharyngeal and oesophageal epithelium contained eosinophilic club cells. Lamina propria of the oro-pharynx contained dense collagen connective tissue in the adult. Muscularis mucosa was absent in all groups. The oesophageal tunica muscularis was composed of skeletal muscle fibres arranged in an inner longitudinal and outer circular layers in juveniles. In the adult oesophagus, the circularly oriented muscle fibres predominated and were interspersed with bundles of longitudinal muscle fibres. An intermediate region between the adult oesophagus and stomach (oesogaster) was characterized by presence of stratified mucous epithelium and gastric gland within the lamina propria. The entire stomach surface was covered by simple columnar mucous epithelium at the base of which were intraepithelial leukocytes. In all age groups, the cardiac and fundic regions of the stomach contained glands in the lamina propria while the pyloric region lacked these glands. The pyloric sphincter was comprised of thickened circular smooth muscle coat in all age groups. The proximal intestine in all ages presented complex labyrinthine mucosal folds, the luminal parts of which bore villar extensions. The middle and distal intestinal mucosa presented simple finger-like mucosal folds in all age groups. The intestinal epithelium in all groups comprised of simple absorptive columnar cells with brush border, intraepithelial leukocytes and goblet cells. The tunica muscularis contained a myenteric plexus in all groups. Carbohydrate histochemistry in all ages under study revealed positive reaction to PAS in the oesophageal mucous cells, stomach simple columnar epithelium and intestinal goblet cells. At pH 2.5, the oesophageal mucous cells and intestinal goblet cells were positive to AB reaction but the stomach epithelium was AB negative in all groups. On subjecting the mucin containing entities to combined AB and PAS reaction after diastase pre-treatment, the oesophageal and oro-pharyngeal wall mucosa presented mixed acid and neutral mucins in all the age groups. The stomach presented only neutral mucins while the intestine presented mixed mucin with acid mucin dominating in the adult proximal intestine. The presence of stratified mucous epithelium observed in the oro-pharyngeal wall and oesophagus is for protection of the tract from abrasion from rough feed. The mucin in the oesophagus is also associated with pregastric digestion of food since the teleost digestive tract lacks salivary glands. The eosinophilic club cell is for non-specific immunity. The taste buds seen in the adult group is for selection and rejection of food materials by gustation. The oesogaster seen in the adult group suggests a structure involved in increasing surface area for gastric digestion and production of extra mucin to reduce the effect of acidic gastric content. The glands in the stomach lamina propria contain oxyntopeptic cells that produce both hydrochloric acid and pepsinogen. The absence of gastric glands in the pyloric region may be an adaptation to reduce the quantity of gastric acid that enters the proximal intestine that needs an alkaline medium for maximal activity of pancreatic enzymes. The reticulated labyrinthine mucosal folds in the proximal intestine increases surface area for feed digestion and absorption. The increasing number of goblet cells towards the rectum is for increased mucin production to reduce abrasion from fecal materials. The acid mucin seen is associated with protection against mechanical injury from food fibres and pathogenic agents while the neutral mucin is involved in pre-gastric digestion in the oesophagus, buffering the effect of gastric acid in the stomach and transport of small molecules in the intestine