Biomonitoring of post-stress adaptive changes in the digestive organs of sterlet in conditions of a recirculating aquaculture system

Purpose. To analyze the peculiarities of post-stress adaptive changes in the digestive system of sterlet at the micro level in conditions of a recirculating aquaculture system. To investigate the dynamics of changes in the cellular composition of the liver, small intestine and pancreas during the adaptation period. To determine the prospect of using the data of histological monitoring in fish breeding practice in order to assess the morphological and functional status of fish. Methodology. Primary materials were obtained in the conditions of an experimental private enterprise "Oasis Bisan". Cameral processing of ichthyological samples was carried out in accordance with generally recognized methods and guidelines. Histological studies were carried out using in-house equipment and original techniques specially designed for the diagnosis of fish tissue. The obtained results were processed by the methods of variation statistics using MS Excel with an emphasis on standard errors. Findings. Microanatomical studies showed that the adaptation of sterlet to the conditions of a recirculating aquaculture system after transportation was 12 days. According to the monitoring results, the most contrasting adaptive changes to new conditions of captivity were noted in the marginal zone of the liver, the small intestine and the pancreas. Under the potential effect of a stress factor, a shift in cell function was noted in the form of shifts in cytological characteristics in the liver. An increase in the linear dimensions of hepatocytes by 1.54 times adequately leads to an increase in the values of the parameters of nuclei by 1.44 times. This is an indicator of a change in the character of intracellular metabolism. Low values of the number of intracellular cavities at the beginning of adaptation are a direct evidence of attenuation of the lipostatic function of hepatocytes. Low values of the “nucleolus/nucleus” diameter ratio (0.40 and 0.41) indicate a change in cellular function in the form of increased glycogen synthesis. During the period of action of the stress factor, the absorption of the components of the chyme in the small intestine occurs with less intensity. Local accumulation of absorbed particles in the cytoplasm indicates a slowdown in digestive processes. After 8 days, under adequate conditions of feeding and maintenance in the mucous membrane of the small intestine, the appearance of goblet glandulocytes can be observed. This fact indicates the normalization of intestinal functioning. The initial period of adaptation practically coincides with the peak of the maximum stress state. At this moment, attenuation of the secretory activity of the pancreas was observed. A significant decrease in the intensity of zymogen biosynthesis leads to the predominance of acinocytes in the volume of the homogeneous pole over the zymogen pole. In the process of adaptation of fish to new conditions of feeding and keeping, acinocytes acquire a specific form. Proteinases and lipases at the end of the secretory cycle of cells exist mainly in an active form and are detected by light-optical methods in the form of a mass of zymogenic granules. Originality. The paper presents new and significantly updated existing data on the adaptation of sterlet organs and tissues under stress and post-stress adaptation. For the first time, a comparative histological analysis of the structure of the marginal zone of the liver, small intestine and pancreas of age-1+ sterlet individuals was carried out.