Carbohydrate histochemistry of the alimentary canal of the shi drum, Umbrina cirrosa L

Morpho-histochemical adaptations of the digestive tract in Gangetic mud-eel Ophichthys cuchia (Hamilton 1822) support utilization of mud-dwelling prey

Freshwater mud-eel, Ophichthys cuchia is nocturnal, carnivorous and economically important fish, yet its digestive physiology is unknown. We therefore studied the gastrointestinal (GI) tract of O. cuchia using morphological, osteological, histological and histochemical approach to understand how the structural adequacy of GI tract helps in acquisition of bottom and mud-dwelling prey and supports utilization of uncommon food resources. Morphologically the GI tract showed typical features of carnivorous fishes in the form of sub-terminal mouth, short muscular esophagus, expendable stomach, short intestine and rectum. Osteological investigation clearly showed that the specialized arrangement of teeth in the oral cavity and pharyngeal region helps in digging and manipulation of bottom and mud-dwelling prey. Longitudinal mucosal folds, stratified squamous epithelium with numerous goblet cells of esophagus protect mucosa from mechanical harm and also allow easy transit of prey into the stomach. Large-sized rugae of stomach are complemented with numerous gastric glands which together increase the transit time of carnivorous food stuff and ensure its complete digestion. The pylorus specifically allows only digested and finely ground food stuff into the intestine and thus avoids the intestinal blockage due to entry of undigested food. The enterocytes and goblet cells of intestine are absorptive and lubricative in their functions respectively. A significant increase in the number of goblet cells and thickness of muscularis from the intestine to the rectum was evident which facilitates the easier transit of food, protection for the epithelium from abrasion, and helps in defecation. Histochemistry revealed that the mucins are secreted throughout the GI tract and thus catalyze faster digestion of carnivorous food stuff, providing protection to mucosal membrane from abrasion, acts as a co-factor to support digestion, absorption of proteins, ions, fluids and helps in defecation. The outcome of this study clearly supports the notion that structural adaptations in the digestive tract of fishes can be effectively used as a blueprint to understand why and how particular fish species feed and use unique food. Additionally, the structural and functional adequacy of the digestive tract helps the fishes to acquire and utilize novel habitats and food resources. The results presented in this study will serve as a reference point for future studies, which focus primarily on understanding the evolution of carnivory in Synbranchids.

Comparative histochemical study of the gastrointestinal tracts of the Nile tilapia (Oreochromis niloticus) and the hybrid catfish (Clarias batrachus x Clarias gariepinus)

Because of the wide variety of cells which are arrayed in the tissue of the gastrointestinal tracts of these two fish, basic histological examination is not appropriate to clarify the histological structure. But histochemical techniques can be applied to identify the chemical differences contained in the tissues. The present study aimed to compare the histochemical characteristics of the gastrointestinal tracts of adult fishes which consume different types of food: the Nile tilapia is herbivore and the hybrid catfish is carnivore. The esophagus, stomach and intestine of each fish was stained with 1) Masson's trichrome, for the muscular and connective tissues, 2) Periodic acid Schiff, for neutral mucin, 3) Alcian blue pH 2.5 and pH 1.0, for acid and sulfated acid mucin. The neutral and acid mucins were observed in the esophagus of the tilapia and catfish but sulfated acid mucin was found only in the catfish. Both neutral and acid mucins presented in the stomach of the tilapia, whereas the stomach of the catfish contained only the neutral mucin although it is contained more collagen in the submucosa. The tilapia intestine revealed that neutral and acid mucins were presented throughout the tissue, and small amounts of sulfated acid mucin were observed in the anterior intestine. However, sulfated acid mucin was very obviously located in posterior intestine of the catfish. Moreover, all parts of the catfish intestine showed both neutral and acid mucins with a thick collagen layer in the submucosa. This research will be useful for understanding the physiology of the relevant digestive systems and making a diagnosis of some gastrointestinal diseases in these two fish.

Skeletal ontogeny of the vertebral column and of the fins in shi drum Umbrina cirrosa (Teleostei: Perciformes: Sciaenidae), a new candidate species for aquaculture

The osteological development of the vertebral column and fins in shi drum Umbrina cirrosa was studied in order to improve knowledge for its introduction in Mediterranean aquaculture. The osteological development was studied in 171 individuals, of total length (L_T ) from 2·7 to 30·2 mm that were reared under the mesocosm technique. Vertebral ontogeny starts at 3·4 and 4·0 mm L_T , with the formation of the first cartilaginous neural and haemal arches, and spines, respectively, and is completed with the full attainment of epicentrals (12·5 mm L_T ). The formation of vertebral centra occurs between 4·1 and 7·4 mm L_T . Pectoral supports are the first fin elements to develop (3·0 mm L_T ), followed by those of the caudal fin (3·8 mm L_T ), pelvic fin (3·9 mm L_T ) and finally by those of the dorsal and anal fins (4·5 mm L_T ). The caudal fin is the first to develop fin rays and attain the full count of principal fin rays (4·5-6·8 mm L_T ), but the last to be fully completed with the formation of procurrent fin rays (6·9-17·5 mm L_T ). The next fins starting to present rays are the dorsal (5·3 mm L_T ) and the pectoral fins (5·6 mm L_T ), while the anal and pelvic fins are the last (5·7 mm L_T ). Following the caudal principal fin rays (6·8 mm L_T ), the dorsal, anal (6·9 mm L_T ), pelvic (7·4 mm L_T ) and pectoral fins (9·8 mm L_T ) are the next with fully completed ray counts. Aggregation of qualitative changes, such as the appearance of cartilages, the beginning and the complement of the ossification process and the full complement of elements in U. cirrosa were measured as cumulative frequency counts. These measurements reveal three ontogenetic intervals: one very developmentally active period during early life stages (from 3 to 5·9 mm L_T ), a second slower developmental period (from 6·0 to 8·9 mm L_T ) and finally a period of ontogeny more focused on structure refinement up to metamorphosis and settlement (>9·0 mm L_T ).

Histochemical and biometric study of the gastrointestinal system of Hyla orientalis (Bedriaga, 1890) (Anura, Hylidae)

This study was carried out to assess the localization of hyaluronic acid (HA) and the distribution of glycoproteins in the gastrointestinal system of adult Hyla orientalis. Histochemical analysis of the gastrointestinal system in H. orientalis showed that mucous content included glycogene and/or oxidable dioles [periodic acid/Schiff (PAS)+], neutral or acid-rich (PAS/AB pH 2.5+), sialic acid residues (KOH/PAS+) and acid sulphate [Aldehyde fuchsin (AF)+] glycoproteins. However the mucus content was not the same in stomach, small and large intestine. The mucus content of stomach included only glycogene and/or oxidable dioles and sialic acid residues. Besides these histochemical methods, the localization of HA was detected using biotinylated hyaluronic acid binding protein labeled with streptavidin-fluorescein isothiocyanate (FITC). In the extracellular matrix of the submucosa, the reaction for HA was evident. Since HA was located in submucosa beneath the epithelial layer of gastrointestinal system, it has a significant role in hydric balance, and essential to provide the gastrointestinal system integrity and functionality. According to biometric results, there were statistical differences between small and large intestine in terms of the amount of material stained positive with PAS/AB, PAS, KOH/PAS and AF/AB. Additionally, number of goblet cells in the small and large intestine was significantly different.

Comparative Histomorphological Studies on Oesophagus of Catfish and Grass Carp

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.

Goblet cell types in intestine of tiger barb and black tetra (Cyprinidae, Characidae: Teleostei)

Histochemical properties of goblet cells in intestine of a stomach-less teleost, tiger barb (Puntius tetrazona), and a stomach-containing teleost, black tetra (Gymnocorymbus ternetzi), are described and compared. The intestine goblet cells were mostly wide in both species, but in tiger barb, some of them were markedly thinner. In black tetra, all the intestine goblet cells displayed magenta colour after PAS, whereas in the tiger barb, only the thinner goblet cells displayed such affinity. The latter cell type was coloured strongly magenta when the tissue was treated with alcian blue (pH 2.5) followed by PAS, whereas the wide goblet cells in tiger barb and all goblet cells in black tetra displayed mainly a blue colour after such treatment. Further, the goblet cells in both species were coloured cleanly blue after high iron diamine followed by alcian blue (pH 2.5). The intestine goblet cells in both species displayed a moderate affinity to WGA and concanavalin A lectins and no affinity to DBA. Most of the goblet cells displayed no affinity to PNA, but some of them in the tiger barb displayed a moderate or strong affinity to this lectin. The affinity to WGA was somewhat strengthened after pre-treatment with neuraminidase. These results suggest that tiger barb contains two types or variants of intestinal goblet cells: high numbers of wide cells filled by acidic, non-sulphated mucin and some thinner cells filled by neutral mucin. The intestine goblet cells in black tetra were filled by variable amounts of neutral and acidic mucin, but the total number of such cells is much less than in tiger barb. The present lectin and neuraminidase results suggest that the intestinal mucins in both species contain significant amounts of N-acetylglucosamine, sialic acid and glucose/mannose, but seem to lack N-acetylgalactosamine. However, some of these cells in tiger barb contain moderate to large amounts of galactose. Together, these results suggest significant species-specific features of the intestine goblet cells and mucin types in tiger barb and black tetra. In conclusion, the present results suggest that the diet and feeding habits in stomach-less teleosts compared with stomach-containing teleosts, greatly influence the number of intestine goblet cells and type of mucin in these cells.

Characterization of cholecystokinin-producing cells and mucus-secreting goblet cells in the blacktip grouper, Epinephelus fasciatus

The characteristics and distributions of cholecystokinin (CCK)-producing cells and mucus-secreting goblet cells were investigated in the digestive tract of the blacktip grouper (Epinephelus fasciatus). CCK-producing cells were scattered throughout the digestive tract. The highest frequency of CCK-producing cells was observed in the anterior intestine portion and pyloric ceca, with a very small number of cells distributed as far as the rectum. Mucus-secreting goblet cells were found to differ remarkably in their regional distributions and relative frequencies. High frequencies of mucus-secreting goblet cells were found in the digestive tract, mainly in the anterior intestine portion and pyloric ceca, but not the esophagus; the frequency decreased slightly toward the rectum. Our result suggests that food digested by gastric acid in the stomach moves on the anterior (including the pyloric ceca) and mid intestine portion, thereby ensuring effective stimulation of the CCK-producing cells. In addition, the distribution pattern of the CCK-producing cells closely resembled that of mucus-secreting goblet cells. In E. fasciatus, CCK-producing cells and mucus-secreting goblet cells seem to be well adapted to promoting optimal control of the digestive process.

Effect of nutrition and Enteromyxum leei infection on gilthead sea bream Sparus aurata intestinal carbohydrate distribution

The effect of a practical plant protein-based diet containing vegetable oils (VO) as the major lipid source on the mucosal carbohydrate pattern of the intestine was studied in gilthead sea bream Sparus aurata challenged with the myxosporean parasite Enteromyxum leei. Fish fed for 9 mo either a fish oil (FO) diet or a blend of VO at 66% of replacement (66VO diet) were exposed to parasite-contaminated water effluent. Samples of the anterior, middle and posterior intestine (AI, MI and PI, respectively) were obtained for parasite diagnosis and histochemistry. Fish were categorised as control (C, not exposed), early (E) or late (L) infected. Mucin and lectin histochemistry was applied to detect the different types of mucins and sialic acid in goblet cells (GC), the brush border and enterocytes. The number of GC stained with periodic acid Schiff (PAS), alcian blue (AB), aldehyde fuchsin-alcian blue (AF-AB), for the detection of neutral, acidic, sulphated and carboxylic mucins, and with the lectin Sambucus nigra agglutinin (SNA), were counted in digital images. The 66VO diet produced a significant decrease of GC with neutral and acidic mucins in the AI and MI, and also of those with carboxylic mucins and sialic acid in the MI. Sulphated mucins and sialic acid were less abundant in the AI than in the MI and PI in the C-66VO treatment. E. leei infection had a strong effect on the number of GC, as E and L infected fish had a significant decrease of GC positive for all the stains versus C fish in PI. Time and diet effects were also observed, since the lowest values were mostly registered in E-66VO fish in PI. In conclusion, though GC depletion was mainly induced by enteromyxosis, an effect of the diet was also observed. Thus, the diet can be a predisposing factor that worsens the disease course.

Morphological and histochemical investigations of esophagogastric tract of a lizard, Laudakia stellio (Agamidae, Linnaeus 1758)

Histological structures of esophagus and stomach tissue samples of Lacerta stellio have been studied, and glycosaminoglycan (GAG) distribution has been histochemically determined. Histologically, esophagus and stomach of L. stellio are composed of four layers: mucosa, submucosa, muscularis mucosae and serosa. Mucosa of esophagus is covered by simple columnar ciliated epithelium with many mucous secreting goblet cells and contains branched tubular glands.Stomach of L. stellio is composed of fundus (oral and aboral) and pylorus regions. Mucosa is covered by columnar epithelium. Fundic glands are branched tubular glands while pyloric glands are usually simple tubular glands. In both regions of the stomach, glands are subdivided into three areas as base, neck and isthmus. Both in the esophagus and stomach, muscular layer is in the form of smooth muscle having inner circular and outer longitudinal layers.According to the results obtained by Alcian Blue (pH 5.8)/Periodic Acid Schiff staining, stomach is similar to esophagus in that neutral mucins and hyaluronic acid (HA) are dominant in isthmus and neck regions of gland tissue of stomach. In the base of the stomach, only neutral mucins have been observed. HA has been observed to be dominant in all other regions of both stomach and esophagus, along with some but not much sulphated GAGs.

Morphology and lectin-binding sites of pyloric caeca epithelium in normal and GnRH-treated Atlantic bluefin tuna (Thunnus thynnus) Linnaeus 1758

Mucosal epithelium of pyloric caeca was studied in normal and in GnRH-treated Atlantic bluefin tuna Thunnus thynnus L., using morphological analysis, conventional and lectin glycohistochemistry. The lining epithelium consisted of columnar (absorptive) cells, goblet cells and intraepithelial leucocytes. The epithelium from normal animals was significantly taller than GnRH-treated samples. Conventional histochemistry displayed the same staining pattern in normal and hormone-treated specimens which showed a mixture of neutral and sulphated acidic glycoconjugates in the luminal surface and goblet cells, and neutral glycans in apical granules of enterocytes. Lectin histochemistry revealed a different glycoconjugate pattern in normal and GnRH-treated tunas. In normal specimens the luminal surface expressed sialoglycoconjugates which bound MAL II, SNA, KOH-sialidase-PNA, KOH-sialidase-SBA as well as asialoglycans stained with HPA, SBA, GSA I-B4 , LTA. N-linked glycans were highlighted by Con A and KOH-sialidase-WGA. In GnRH-treated tunas the luminal surface did not react with SNA, SBA and LTA. The columnar cells of normal tunas bound KOH-sialisase-PNA in the apical region, KOH-sialidase-PNA, KOH-sialidase-DBA, HPA, SBA, KOH-sialidase-SBA and KOH-sialidase-WGA in apical granules, GSA I-B₄ and LTA in the supranuclear region. GnRH-treated specimens showed some columnar cells that stained with KOH-sialidase-WGA in the apical granules and with GSA I-B4 in the supranuclear region. The goblet cells of normal animals produced mucins positive to PNA, HPA, KOH-sialidase-DBA, SBA, GSA II. The latter three binding sites lacked in GnRH-treated tunas. The results suggest that the mucosal epithelium of Thunnus thynnus L. pyloric caeca expresses a complex glycan pattern that is affected by GnRH-treatment.

Histochemical studies on mucin-rich cells in the digestive tract of a teleost, the Buenos Aires tetra (Hyphessobrycon anisitsi)

Types of mucus cells and mucins in the epithelial cell layer throughout the digestive tract of the Buenos Aires tetra (Hyphessobrycon anisitsi) are described and compared. The mucin was produced in three different cell types: in sac-like cells in the esophagus, in surface epithelial cells in the stomach and in goblet cells in the caeca and intestine. Nearly the entire esophageal epithelial cell layer consisted of mucus cells, filled by both neutral mucin and non-sulfated acidic mucin. The gastric mucin occurred in the distal area of the surface epithelial cells only and contained mainly neutral proteoglycans rich in glucosamine and some galactosamine and sialic acid. The goblet cells contained mainly non-sulfated acidic mucin in the caeca and sulfated acidic mucin throughout the entire intestine. Much glucosamine and some galactosamine and sialic acid occurred regularly in these cells in both the caeca and intestine. The observation that goblet cells often displayed colors ranging between blue and purple-magenta when alcian blue staining was followed by periodic acid-Schiff (PAS), or between blue and red-brown when the alcian blue was followed by neutral red, may reflect different ages or stages of development and differentiation for these cells. The highly variable affinities to wheat germ agglutinin (WGA-lectin) seen in these cells in the present study strengthens this view. However, such results may also suggest a true cellular heterogeneity reflecting various roles in lubrication, immunological defence, digestion and absorption.

Mucus cells in the digestive tract in prenatal platyfish larvae (Poeciliidae, Teleostei)

The appearance and histochemical properties of mucus cells in various parts of digestive tract in prenatal larvae of platyfish (Xiphophorus maculatus), a stomachless teleost, are described and compared. Such cells occurred regularly throughout the entire epithelial cell layer in mouth, pharynx, oesophagus and intestine in 6 mm long larvae i.e. approximately 1 week before delivery, but were very scarce in 4 mm long larvae. The mucin in these cells was strongly stained by alcian blue at pH 2.5 and weakly coloured by this dye at pH 1.0. It displayed a clean blue colour after high iron diamine followed by alcian blue (pH 2.5), except in some very few cells which displayed a purple-brown colour after this treatment. The mucus cells displayed various colours between purple-blue and magenta when the alcian blue (pH 2.5) was followed by periodic acid-Schiff (PAS) solution; the magenta-coloured cells were mainly confined to oesophagus. Together these findings suggest that the mucin in the digestive tract of prenatal platyfish consists mainly of non-sulphated, carboxylated glycoconjugates. The observations from the present lectin histochemistry suggest that the amount of galactosamine and glucosamine in this mucin varies much from cell to cell. Also, the various colours after PAS suggest a significant cellular heterogeneity in the mucus cell population. This may reflect different stages in development and maturation or a true and permanent cellular heterogeneity, suggesting that this mucus is able to play a number of important roles even a week before the larvae start to feed and digest.

Histochemical study on the intestine goblet cells in cichlid and poecilid species (Teleostei)

Histochemical properties of intestine goblet cells in firemouth cichlid, zebra mbuna, freshwater angelfish and platyfish are described. Goblet cells occurred regularly in the epithelial cell layer throughout the entire intestine, they were strongly coloured by alcian blue at pH 2.5. This colour got gradually weaker when the pH was reduced, but still after alcian blue at pH 0.2 these cells displayed a distinct blue colour. When the goblet cells were treated with periodic acid-Schiff (PAS), they displayed a strong purple-magenta colour. The findings that a number of goblet cells displayed various colours between blue and purple-magenta when acidic alcian blue was followed by PAS, and between blue and red-brown when acidic alcian blue was followed by neutral red, may reflect different ages or stages of development and differentiation for these cells. However, such results may also suggest a true cellular heterogeneity in the present population of goblet cells, reflecting that the intestine mucus layer has a number of roles in teleosts like lubrication, protection, immunological defence, digestion and absorption. In the ferritin injected specimens of firemouth cichlid and platyfish, a number of macrophage-like cells in intestine wall displayed Prussian blue precipitations in tissue treated with acid ferrocyanide, suggesting that these cells play a cleansing role in the intestinal wall. No ferritin uptake was seen in the intestine goblet cells and eosinophilic granule cells.

Histology and mucin histochemistry of the digestive tract of yellow catfish, Pelteobagrus fulvidraco

The histology and characteristics of mucins secreted by epithelial mucous cells of the digestive tract in yellow catfish, Pelteobagrus fulvidraco were investigated using light microscope and transmission electron microscope. The digestive tract was divided into a pharynx, oesophagus, U-shaped stomach (with a cardiac, fundic and pyloric part) and intestine, composed of anterior intestine, middle intestine and posterior intestine, which consisted of a mucosa (epithelial layer), lamina propria-submucosa, muscularis and serosa. A large number of isolated longitudinal striated muscular bundles were present in the lamina propria-submucosa of pharynx. Goblet cells were observed throughout the digestive tract, except in the stomach. In the cardiac and fundic stomach, a plenty of gastric glands were observed, whereas they were absent in the pyloric part. Numerous mitochondria and endoplasmic reticulum were observed in the columnar epithelial cells of the intestine, especially of the anterior part. The epithelial mucous cells contained neutral or other two mixtures of acid and neutral mucins, the first being the most common. The neutral mucin was the only type of mucins in the stomach, anterior intestine and middle intestine. The results of this study will be helpful for understanding the digestive physiology and diagnosing some gastrointestinal diseases in yellow catfish.

Glycoconjugates in the mucosa of the digestive tract of Cynoscion guatucupa: a histochemical study

This study addresses the histomorphology, the histochemistry and the distribution of glycoconjugates (GCs) in the mucosa of the digestive tract of the weakfish Cynoscion guatucupa. The histological characterization of the buccopharyngeal cavity and the esophagus revealed that they are lined by a stratified epithelium where the mucosa is thrown into longitudinal folds. The stomach is lined with a simple columnar secretory epithelium with tubular glands. GCs were analyzed using a range of histochemical methods. They were identified as oxidizable vicinal diols; sialic acids and some of their chain variants, C7, C8 or C9; sialic acid residues with O-acyl substitution at C8 or C9; carboxyl groups and sulfate groups. Sugar residues in the oligosaccharide side chains of the GCs were investigated using seven biotinylated lectins. Mucous cells from the contents of the buccopharyngeal cavity, esophagus and stomach evidenced neutral, sulphated and sialylated GCs. The latter were substituted mainly in C8. A moderately strong lectin labeling was observed in mucous cells of the three organs studied. Nonetheless, the apical edge of the gastric gland cells showed a strong positive labeling. The presence of different classes of GCs has been associated with different functions, such as lubrication, protection, inhibition of microorganisms proliferation and ionic regulation.

Histochemical characterization of glycoproteins in the buccal epithelium of the catfish, Rita rita

Glycoproteins (GPs) elaborated by the buccal epithelium of the catfish, Rita rita, were analysed by a range of histochemical methods. These included methods for the characterization and simultaneous visualization of GPs with oxidizable vicinal diols, with O-acyl sugars, with O-sulphate esters and with sialic acid residues with and without O-acyl substitution at C7, C8 or C9. GPs elaborated at the surface of the buccal epithelium are primarily from two sources, the epithelial cells and the mucous goblet cells. They include GPs with O-sulphate esters, GPs with sialic acid residues without O-acyl substitution and GPs with oxidizable vicinal diols. Different classes of GPs have been associated with specific functions and are discussed in relation to their physiological significance, with special reference to their roles in lubrication, alteration in viscosity, trapping of food particles, buffering of fluids at the epithelial surface, prevention of proteoloytic damage to the epithelium, antimicrobial activity and defence against pathogens. The epithelium shows specialized modifications in the form of the buccal glands. These have been considered to increase the secretory surface that allows profuse secretion of mucus in a very short period of time. The secretions of these glands have been associated with multiple functions similar to those of saliva.

Histochemical analysis of glycoconjugate secretion in the alimentary canal of Anguilla anguilla L

Conventional histochemical methods as well as lectin-binding techniques were used to study glycoconjugates that are present in the alimentary canal of the European eel (Anguilla anguilla). Specimens from pharynx, oesophagus, stomach and intestine were collected from adult ("silver eel" stage) females. Alcian Blue pH 2.5/PAS and High Iron Diamine/Alcian Blue pH 2.5 reactions were performed to stain neutral and acidic glycoconjugates. In addition, lectin histochemistry was applied to identify acidic glycoconjugates containing O-acylated sialic acids. Finally, the presence of sugar residues in the oligosaccharide side chains of glycoconjugates were investigated by using biotinylated lectins. Acidic and neutral glycoconjugates were found to be secreted throughout the alimentary canal, the acidic glycoconjugates appeared to be either sialylated or sulphated. Sialylated glycoconjugates were identified to contain sialic acid substituted at carbon in position 7 (C7). Sulphated glycoconjugates were particularly abundant in the distal intestine and were not present in the secretory products of the gastric mucosa, which contained a variety of sugar residues (D-N-acetyl-galactosamine, beta-D-galactose, alpha-D-mannose, alpha-L-fucose, D-N-acetyl-glucosamine). Lectin binding was observed in mucous cells of pharynx, oesophagus and intestine, and particularly some monosaccharides (D-N-acetyl-galactosamine and beta-D-galactose) were abundantly present.