Abstract
The paper presents data from ichthyological, trophological and histological studies of the Sandpiper goby (Neogobius fluviatilis) endemic to the Caspian Sea, which has an important role in trophic chains, as food object for sturgeon, semi-migratory fish species, marine migratory Clupeidae family and Caspian seal. Place of sampling for the study were stations in the Northeastern part of the Caspian Sea, which is inferior in trophic content to its other parts, which had confirmed by data from trophic studies. The basis of the studied fish nutrition was Polychaeta, Bivalvia, Crustacea and in some cases juvenile fish, which indicates their nutritional plasticity, and the fact that they are not competitors to each other in nutrition. Depending on results of fish’s visceral organs histological studies, structural changes were determined, which were more adaptive in nature and were a response to the impact of aquatic environment factors. In gills was found protozoan invasion causing hyperplasia of secondary lamellae epithelium and sloughing of respiratory epithelium. There were growths of the epithelial layer of villi in the intestine. In the liver and pancreas were detected fatty degeneration and necrotic changes. In all organs were found microcirculatory disorders, including the presence of erythrocytes with hyperchromic cytoplasm.