This article describes the clinical manifestation of natural Vibrio anguillarum infection in rainbow trout (Oncorhynchus mykiss) during an outbreak on a fish farm. (i) Using an integrated approach, we characterized the pathogenesis of vibriosis from the morphological, hematological, and biochemical points of view. The molecular mechanisms associated with the host immune response were investigated using mass spectrometric analysis of trout plasma proteins. (ii) According to the severity of infection (the extent of tissue damage, the level of expression of pro-inflammatory genes, and changes in the leukocyte profile) three fish populations were identified among infected trout: fish with severe lesions (SL), fish with the moderate infectious process (IP) and asymptomatic fish (AS). (iii) Lymphopenia, granulocytosis, and splenomegaly were strong trends during the progression of infection and informative indicators of severe manifestation of disease, associated with hemorrhagic shock, metabolic acidosis, and massive tissue damage. (iv) As expected, pro-inflammatory interleukins, complement components, acute phase proteins, and antimicrobial peptides were implicated in the acute pathogenesis. Systemic coagulopathy was accompanied by increased antithrombotic reactions. (v) Reconstruction of metabolic pathways also revealed a high energy requirement for the immune response in severely affected fish. (vi) An unexpected result was a small difference between fish with moderate symptoms and fish with no or minor external signs of pathology (putatively resistant to infection). Increased production of antiproteases and enhanced blood coagulation cascade were observed in healthier fish, which may underlie the mechanisms of a controlled, non-self-damaging immune response to infection. (vii) Depending on the progression of the disease and the presence of the pathogen, a stepwise or linear change in the abundance of some plasma proteins was revealed. These proteins could be proposed as molecular markers for diagnosing the health and immune status of trout when cultured in fish farms.

The lipopolysaccharide (LPS)-induced inflammation model is widely used in mammalian studies but remains poorly investigated in a variety of fish species. We reproduce this model in rainbow trout, Oncorhynchus mykiss, a species of high economic value, to validate specific inflammatory biomarkers for reliably assessing the health and immune status of farmed fish. The inflammatory process, together with the effect of preconditioning, was modeled using two consecutive intraperitoneal injections of 300 and 600 µg LPS. We assessed innate immunity biomarkers, including the expression of inflammation-related genes (il1ß, il8), peripheral blood leukocyte profiles, serum bactericidal activity (SBA), and various serum and hepatic biochemical parameters. These parameters comprised the concentration of C-reactive protein (CRP, an acute phase protein), and the activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione-S-transferase) measured at 24 and 96 h post-injection. In trout, LPS-induced effects involved the overexpression of pro-inflammatory interleukins (il1ß, il8), a left shift in white blood cells (characterized by a prevalence of immature neutrophils), and enhanced SBA. In contrast to warm-blooded animals, LPS challenge in trout did not appear to significantly elevate CRP levels or antioxidant enzyme activity. Further investigations in other fish species are needed to determine whether these are traits specific to trout or common to bony fish. Our findings provide a foundation for developing a biomarker panel suitable for the routine assessment of welfare, early detection of infection-associated inflammation in cultured fish, and the screening of the anti-inflammatory and immunostimulant activities of drugs and feed additives.

В статье приведены результаты оценки эффективности применения препарата «Флавомицин 80» в кормах для радужной форели породы Камлоопс при выращивании в установке с системой замкнутого водоснабжения. Показано, что данная кормовая добавка приводит к повышению жизнеспособности годовиков форели и улучшению рыбоводно-биологических показателей рыб. Применение препарата в дозировке 44 мг/кг способствовало снижению интенсивности поражения форели возбудителями бактериозов различной этиологии. Доказан положительный бактериостатический эффект кормовой добавки «Флавомицин 80» на развитие условно-патогенной микрофлоры кишечника рыб.