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Background: The mortality of freshwater fish due to stress during various production manipulations is a severe problem, which requires a thorough understanding of the basic mechanisms involved, including the hemostasis system. Therefore, on the application level, the study of blood clotting can perform fish coagulopathies diagnostics and develop practical preventive and therapeutic anticoagulation methods for fish farming. Aim: The goal of this research was a comparative assessment of the reaction of some hemostasis parameters of two commercial fish species, carp Cyprinus carpio and tilapia Oreochromis niloticus, to the stress of different duration induced by corticosteroids. Methods: The fishes were divided into three groups: chronically stressed (induction by betamethasone), acutely stressed (induction by dexamethasone), and control animals with blood taken from the caudal hemal canal before hormone treatment(by dexamethasone and betamethasone), then 7 and 21 days after. Results and Discussion: Changes in the following parameters were studied: thrombin time, prothrombin time, activated partial thromboplastin time, the concentration of fibrinogen, soluble fibrin monomer complexes, antithrombin. It was found that both hormone-induced stress and handling stress associated with blood sampling strongly increased blood clotting ability in carps (prothrombin time decrease by 78,5-86,1%, fibrinogen increase by 12,7-100%, thrombin time decrease by 83,4-85%, and antithrombin III decreases by 15,3-21,7%), while in tilapias, acceleration of blood clotting by intrinsic and extrinsic pathways were recorded by the end of the experiment only in fishes with imitation of chronic stress (prothrombin time decrease by 76,8%, activated partial thromboplastin time decrease by 20,0%, and 2,3 multiplying soluble fibrin monomer complexes). Conclusions: It was concluded that the adaptive mechanisms of the tilapia (Oreochromis niloticus) organism allowed the clotting function to recover in most cases by the end of the experiment in all groups of fish, in contrast to carps (Cyprinus carpio). Смертность пресноводных рыб в результате стресса при различных манипуляциях на производстве представляет серьезную проблему, что требует глубокого понимания основных задействованных механизмов, в том числе системы гемостаза. На прикладном уровне проведение исследования свертывания крови имеет потенциал для диагностики коагулопатий рыб и разработки практических профилактических и терапевтических противосвертывающих методов для рыбоводства. Цель: Целью этого исследования была сравнительная оценка реакции некоторых параметров гемостаза двух видов промысловых рыб - карпа Cyprinuscarpio и тиляпии Oreochromisniloticus в условиях экспериментальной модели стресса различной продолжительности, индуцированного кортикостероидами. Методы: Рыбы были подразделены на три группы: рыбы с хроническим стрессом (индукция бетаметазоном), острым стрессом (индукция дексаметазоном) и контрольные животные, кровь у которых брали из хвостового гемального канала до обработки гормонами, и далее через 7 и 21 день после. Результаты и Обсуждение: Было исследовано изменение следующих параметров коагулограммы: тромбиновое время, протромбиновое время, активированное частичное тромбопластиновое время, концентрацию фибриногена, растворимых фибрин-мономерных комплексов, антитромбина. Было установлено, что как индуцированный гормонами стресс, так и хэндлинг-стресс, связанным с забором крови, сильно увеличивают свертывающую способность крови у карпов (сокращение протромбинового времени на 78,5-86,1%, увеличение фибриногена на 12,7-100%, сокращение тромбопластинового времени на 83,4-85% и антитромбинаIIIна 15,3-21,7%), тогда как у тиляпий ускорение свертывания крови по внутреннему и внешнему путям к концу эксперимента было зафиксировано только у рыб с имитацией хронического стресса (снижение протромбинового времени на 76,8%, снижение активированного частичного тромбопластинового времени на 20,0%, увеличение фибрин-мономерных комплексов в 2,3 раза). Заключение: Можно отметить, что адаптивные механизмы организма тиляпий позволили свертывающей функции в большинстве случаев восстановиться к концу эксперимента у всех групп рыб, в отличие от карпов. [ABSTRACT FROM AUTHOR]

Carp (Cyprinidae) is one of the dominating and most valuable fish species in fish farming. Under conditions of high-intensity cultivation, fish are systematically exposed to extreme factors that cause stress reactions, accompanied by changes in the functional state of the defense of the body systems and exert impact, primarily, on hematological parameters. The hemostatic system is one such defense systems, which counteracts bleeding through a coagulation mechanism. Hemocoagulation follows the same pattern in all vertebrates, from jawless fish to mammals, and represents an ancient adaptation of animals to stressful conditions, often associated with blood loss in nature. This research aimed to study the effect of hormone-induced stress on plasma (secondary) hemostasis in fish. Given the data fragmentation and differences in methodology and conditions, the lack of standardization in studying hemostasis in fish, especially in critical conditions, this problem remains not fully disclosed in global science. The article presents the results of studying carp (Cyprinus carpio) coagulogram parameters under the influence of acute and chronic stress responses, simulated by injections of synthetic cortisol analogs (dexamethasone for short-term stress, and betamethasone for chronic stress) during 21 days. The dynamics of these indicators were analyzed in comparison to intact fish. It has been established that by accelerating the activated partial thromboplastin time, prothrombin time, and increasing the amount of fibrinogen in the blood of fish, blood coagulation processes were clearly accelerated in all groups of animals tested by the last day of the experiment. The dynamics of other parameters, such as the content of soluble fibrin monomer complexes or antithrombin III content, indicated the simultaneous development of hypercoagulation processes in some groups. Assumptions have been made to explain the pattern of changes observed not only in treated fish but also in control animals. [ABSTRACT FROM AUTHOR]