The biochemical and histochemical properties of intestinal mucin glycoproteins of virus and parasite-free common carp Cyprinus carpio were investigated. The presence of carbohydrates in mucin glycoproteins could be demonstrated by histochemical methods, but generally, no obvious differences in specific staining for mucin glycoproteins were observed in contrast to biochemical techniques. Biochemical staining methods displayed differences in structure and composition of intestinal glycoproteins. Released intestinal glycoproteins contained two types of mucin glycoproteins: type 1 mucins displayed a size of >2000 kDa, and were highly glycosylated, while type 2 mucins ranged between 700 and 70 kDa, and were weakly glycosylated. In epithelial (intracellular) glycoproteins, mainly N-acetyl-a-galactosamine and mannose were found, while in luminal (extracellular) glycoproteins in addition sialic acid was evident. Fucose was not detected. Thus, structure and composition of intestinal glycoproteins of common carp were similar to those found in mammals.

Water in aquaculture systems may contain a high load of microorganisms. Reduction in overall bacterial tank water load improves fish health and growth parameters. In this study, the effect of an increase of overall bacterial load in tank water on carp skin mucus was assessed. Intracellular and released high molecular weight glycoproteins (HMGs) of carp skin mucus were analysed for changes using histological, histochemical and biochemical techniques. Increase of bacterial load did not induce obvious clinical responses in carp, but the skin of exposed carp responded quickly. The amount of skin mucus HMGs isolated increased as well as their total glycosylation. An increased goblet cell number was observed for all carbohydrate stainings, but most clearly for acidic glycoconjugates. A change in the terminal presence of some sugars was also seen. After the initial response of carp, an adaptation to the higher bacterial load in the water appeared to occur as mucins had a higher glycosylation. The changes observed suggest that these skin mucus adaptations are part of a primary defence mechanism of mucosal epithelia, even at a low pathogenic pressure.

Mucins are high molecular weight glycoproteins produced by goblet cells and secreted on mucosal surfaces. We investigated biochemical and histochemical properties of intestinal mucins of virus-and parasite-free common carp Cyprinus carpio in response to a single peroral application of endotoxin (lipopolysaccharide = LPS). Intracellular mucins were quantified histochemically by their carbohydrate content and characterized by specific, lectin-based methods. In addition, secreted epithelial (intracellular) and luminal (extracellular) mucins were isolated and separated by downward gel filtration. Carbohydrate and protein content were determined photometrically. Subsequently, terminal glycosylation was characterized by a lectin-binding assay. A peroral endotoxin application altered intestinal secretion and composition of intestinal mucin glycoproteins in common carp. A statistically significant decrease in mature luminal mucins was demonstrated, linked to a new biosynthesis of intracellular mucin glycoproteins. Simultaneous changes in the glycosylation pattern of isolated mucins were found. The intestinal mucosal system is purported to provide a removal mechanism for bacterial noxes by increasing secretion of mucins inducing a flushing-out effect, in combination with altered glycosylation patterns that change adhesion properties. Consequently, pseudofaeces of fish, which are a common sign of intestinal parasitical infections, may also be interpreted as an elimination mechanism for strong bacterial noxes. KEY WORDS: Carp · Mucus · Intestinum · Endotoxin · Lipopolysaccharide Resale or republication not permitted without written consent of the publisherDis Aquat Org 77: [17][18][19][20][21][22][23][24][25][26][27] 2007 in fish are considered to be similar to those of mammals. As in mammals, there is production of secretory vesicles with neutral, acidic or sulphated glycoproteins (Shephard 1994, Bosi et al. 2005. Histological and histochemical studies also indicate that fishes with parasitic infections (like infected mammals) exhibit goblet cell hyperplasia and hypertrophy, whereby as a chronic reaction their intracellular mucins shift towards acidic and sulphated glycoprotein types (George & Nadakal 1981, Dezfuli et al. 2002, Bosi et al. 2005.However, to our knowledge little information is available on the biochemical composition of piscine glycoproteins and their response to enteric bacterial infections. We mimicked bacterial infection by an oral application of endotoxin. Endotoxins are lipopolysaccharide (LPS)-protein complexes synthesized mainly by gram-negative bacteria. LPS is an integrated part of the bacterial membrane. Endotoxin has, at least in mammals, a local and systemic immune-inducing function in inflammation reactions (Raetz 1990, Raetz & Whitfield 2002. Toxic effects are mainly mediated by cell receptors (TLR-4) and leucocyte mediators; however, there are numerous key differences between fish and mammals. In many in vitro studies on cells of lower vertebrates, such as fish, extremely high co...