The European catfish, Silurus glanis L., has become an important aqua cultural fish in Croatia, and it is cultivated extensively in ponds in polyculture with carps. The development of the digestive tract in S. glanis was studied with the aim of improving intensive fish production. Research was carried out on S. glanis larval stadium from 1- to 19-day post-hatching (DPH). The main histological methods used were: haematoxylin and eosin staining, periodic acid Schiff staining (PAS), Alcian blue (AB) and toluidin blue staining (TB). A yolk sac was present during the first 5 days (1-5-DPH). During the initial 3-DPH period, there was no trace PAS and AB activity in the digestive tract. Differentiation of the digestive tract began at 3- to 5-DPH. The oesophagus was positive for AB at 5-DPH, PAS and TB after 7-DPH. Differentiation of enterocytes began at 5-DPG and the intestines were complete at 11-DPH. Development of liver and pancreas was also studied. The analysis of data obtained in this study suggests that after 5-DPH catfish larvae have morphologically completed digestive tracts.

Histochemical localization of non-specific esterase, alkaline and acid phosphatase in the intestine of free-living goldline (Sarpa salpa L. 1758) was investigated. Fish were caught in the vicinity of the town of Zadar (Adriatic Sea, Croatia), and samples of three parts of the intestine proper (anterior, middle and posterior) as well as the rectum were used for presentation of non-specific esterases, alkaline phosphatase and acid phosphatase. Non-specific esterase activity was found in the cytoplasm and brush border of enterocytes in all investigated intestinal segments and the rectum. The activity was stronger in the middle and posterior part of the intestine but weaker in the anterior segment of the intestine as well as in the rectum. Intestinal alkaline phosphatase was detected in the brush border and supranuclear cytoplasm of enterocytes of all investigated intestinal segments. Enzymatic activity gradually decreased in a posterior direction. Acid phosphatase activity was observed as a fine granular reaction product in the supranuclear region of enterocytes and was almost equal in all investigated intestinal segments as well as in the rectum. The possible role of enzymes in intracellular digestion and transport is discussed.

ABSTRACT:The histopathological structure as well as content and distribution of mucosubstances in the mid-gut mucosa of the honeybee (Apis mellifera) treated with the phyto-pharmacological preparation Nozevit was studied. For the purpose of describing neutral, acid and sulphate mucopolysaccharides we used the Periodic Acid-Schiff Reaction (PAS), Alcian blue-specific (pH = 1.0 and 2.5) and Toluidine blue-specific staining. Based on our results we have concluded that the herbal preparation Nozevit induces the production and secretion of mucous from the epithelial layer of treated bees, and additionally coats the peritrophic membrane to form a firm and resilient envelope. Thus, the preparation may ensure protection from new invasion with Nosema sp. spores and also from normal physiological processes.

Diet-related differences between the ratio of intestine length to body size and the enzymatic activity in the intestinal tract of wild and reared European eel (Anguilla anguilla L.) were studied. Compared with reared eel, wild eel showed significantly shorter relative intestine length. For the purpose of histochemical examination, different parts (anterior, middle and posterior) of intestine proper were used. Activities of non-specific esterase, alkaline and acid phosphatase, and aminopeptidase were examined in each segment. All enzymes were present in the intestines of both wild and reared European eel. Fish from both groups showed similar enzyme distribution within the enterocytes, but distribution and intensity of enzyme activity along the intestine vary depending on the group. Generally, reared European eel showed highest enzymatic activity and wider distribution of enzymes throughout all parts of the intestine. These results suggest that different diets could be one of the reasons for observed changes.

214 SummaryThe presence of metacercariae of Centrocestus formosanus was detected on the gills of goldfish (Carassius auratus L.) imported from Singapore and obtained from two pet shops. This is the first report of the parasite in Croatia. The histopathological changes observed lead to the conclusion that the infection could be one of the reasons for the death of goldfish.