Light microscopic characterization of glycoconjugates in secretory cells of the carp (Cyprinus carpio) gill epithelium

Histochemical distribution of four types of enzymes and mucous cells in the intestine of koi carp (Cyprinus carpio var. koi)

The main purpose of this study was to investigate the distribution of acid phosphatase (ACP), alkaline phosphatase (ALP), non-specific esterase (NSE), peroxidase (POD), and mucous cells in the intestine of the koi carp Cyprinus carpio var. koi. ACP activity was located in the striated border, enterocytes, and lamina propria of the anterior and middle intestines. The ACP activity in the anterior intestine was higher than that in the middle and posterior intestines. ALP existed in the striated border of enterocytes and lamina propria, serosa, muscular layer, and the junction between muscular layer and submucosa layer of the intestine. The ALP activity in the anterior intestine was higher than that in the middle and posterior intestines. NSE activity was localized in the cytoplasm of enterocytes in the whole intestine, and the middle intestine showed the lower NSE activity than the anterior and posterior intestines. POD activity was localized in the blood cells of the lamina propria and cytoplasm of enterocytes in all intestinal segments. The POD activity among the anterior, middle, and posterior intestines was non-significantly different. Alcian blue periodic acid-Schiff histochemical results revealed three types of mucous cells in the intestine. The total number of mucous cells and percentage of type I cells among the anterior, middle, and posterior intestines were non-significantly different. The percentage of the type II cells was the highest in the posterior intestine, while the lowest in the anterior intestine. The percentage of the type III cells was the highest in the anterior intestine, while the lowest in the posterior intestine.

Blood cues induce antipredator behavior in Nile tilapia conspecifics

In this study, we show that the fish Nile tilapia displays an antipredator response to chemical cues present in the blood of conspecifics. This is the first report of alarm response induced by blood-borne chemical cues in fish. There is a body of evidence showing that chemical cues from epidermal 'club' cells elicit an alarm reaction in fish. However, the chemical cues of these 'club' cells are restricted to certain species of fish. Thus, as a parsimonious explanation, we assume that an alarm response to blood cues is a generalized response among animals because it occurs in mammals, birds and protostomian animals. Moreover, our results suggest that researchers must use caution when studying chemically induced alarm reactions because it is difficult to separate club cell cues from traces of blood.

Alteration of photoresponses involved in diel vertical migration of a crab larva by fish mucus and degradation products of mucopolysaccharides

Photoresponses involved in the descent phase of nocturnal diel vertical migration (DVM) of larvae of the crab Rhithropanopeus harrisii were measured in a laboratory system that mimicked the underwater angular light distribution. The test hypothesis was that kairomones from fish that activate zooplankton photoresponses involved in DVM are derived from polysaccharides from the external mucus of fishes. Studies considered fish mucus from the mummichog (Fundulus heteroclitus) and disaccharides (originating from chondroitin sulfate A and heparin polysaccharides) that are likely constituents of fish mucus. R. harrisii larvae descend at sunrise with an isolume and remain near the isolume during the day. Since depth maintenance near the isolume depends upon a negative phototaxis, the lowest light intensity (threshold) that induces this response was used to quantify the effects of the test chemicals. It was predicted that exposure to fish kairomones would lower the photoresponse threshold, thereby resulting in larvae remaining deeper in the water column where light for visual predation was reduced. The photoresponse threshold declined as the concentration of fish mucus increased. Disaccharides originating from chondroitin sulfate A and heparin also decreased the photoresponse threshold as compared to responses in aged, filtered seawater. Collectively, the results support the hypothesis and indicate that disaccharide degradation products of predator mucus containing sulfated and acetylated amines can serve as kairomones.

Lectin histochemistry of rainbow trout (Oncorhynchus mykiss) gill and skin

In order to characterize the glycoconjugate residues in skin and gills of the adult rainbow trout, the binding pattern of five biotinylated lectins with different carbohydrate specificities was examined. In the skin, mucous cells revealed binding sites for PNA and SBA; filament-containing cells were additionally labelled with Con A. However, the basal cell layer showed no reaction. In the gill, subpopulations of mucous cells reacted with Con A, PNA, SBA and UEA-I. This broader spectrum of glycoconjugates in gill mucous cells compared with the epidermal mucous cells could point to the additional function of gill mucus in ion and osmoregulation. Lectin binding sites were less common in the respiratory epithelial cells of the secondary lamellae than in those of the primary lamellae. Chloride cells revealed mannose, galactose and fucose residues. Immature chloride cells, as indicated by a comparison with Na+/K+ ATPase immunolabelling, reacted with Con A; subpopulations of them reacted with PNA, SBA and UEA-I. The results form the basis for further investigations in which these cell populations can be analysed under different environmental conditions.