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.

The implantation of optical sensors is a promising method for monitoring physiological parameters of organisms in vivo. For this, suitable hydrogels are required that can provide a biocompatible interface with the organism’s tissues. Amorphous hydrogel is advantageous for administration in animal organs due to its ease of injection compared to resilient analogs. In this study, we investigated the applicability of a semi-liquid 2.5% polyacrylamide hydrogel (PAAH) as a scaffold for fluorescent polyelectrolyte microcapsules (PMs) in rainbow trout. The hydrogel was injected subcutaneously into the adipose fin, which is a small, highly translucent fold of skin in salmonids that is convenient for implanting optical sensors. Using histological methods, we compared tissue organization and in vivo stability of the applied hydrogel at the injection site after administration of uncoated PMs or PMs coated with 2.5% PAAH (PMs-PAAH) for a period of 3 to 14 days. Our results showed that the introduction of PMs into the gel did not have a masking effect, as they were recognized, engulfed, and carried away by phagocytes from the injection site. However, both PMs and PMs-PAAH were found to provoke chronic inflammation at the injection site, although according to cytokine expression in the fish spleen, the irritating effect was local and did not affect the systemic immunity of the fish. Therefore, our study suggests low applicability of 2.5% polyacrylamide as a scaffold for injectable sensors within a timeframe of days.

The article presents the results of quantitative indicators of the growth of rainbow trout when growing feed with a partial replacement of animal proteins with plant proteins. The results obtained show that the growth rate of fish and the feed coefficient when replacing protein by 10% with plant proteins do not change, provided that the animal, as well as the macro- and microelement balance of feed, are observed.

The paper studied the effect of feed bioadditives Levabon Rumen E and Digestarom P.E.P. 1000 and a complex of organic acids on the dynamics of mass accumulation, indices of visceral organs, anatomical pathological changes, and hematological parameters of juvenile trout. The maximum positive effect on the morphophysiological parameters and health of fish was revealed for yeast in combination with a phytobiotic as a feed bioadditive. The immune response was found to increase in fish fed bioadditives. A complex of organic acids adversely affects the state of the visceral organs and tissues of fish. A combined use of feed additives in the diet of juvenile trout is recommended in the following concentrations: 2% Levabon Rumen E and 1.5% Digestarom P.E.P. 1000. This combination helps to reduce intensive development of pathological processes in adult fish and improve the physiological parameters of juvenile trout.

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.