Species with effective thermal adaptation mechanisms allowing them to thrive within a wide temperature range can benefit from climatic changes as they can displace highly specialized species. Here, we studied the adaptive capabilities of the Baikal endemic amphipods Eulimnogammarus verrucosus (Gerstfeld, 1858) and Eulimnogammarus cyaneus (Dybowsky, 1874) compared to the potential Holarctic Baikal invader Gammarus lacustris Sars, 1863 at the cellular level including the energy metabolism and the antioxidant system. All species were long-term exposed to a range of temperatures (1.5 °C to mimic winter conditions and the three species-specific preferred temperatures (i.e., 6 °C for E. verrucosus, 12 °C for E. cyaneus and 15 °C for G. lacustris). At 1.5 °C, we found species-specific metabolic alterations (i.e., significantly reduced ATP content and lactate dehydrogenase activity) indicating limitations on the activity level in the Holarctic G. lacustris. Although the two Baikal endemic amphipod species largely differ in thermal tolerance, no such limitations were found at 1.5 °C. However, the cold-stenothermal Baikal endemic E. verrucosus showed changes indicating a higher involvement of anaerobic metabolism at 12 °C and 15 °C, while the metabolic responses of the more eurythermal Baikal endemic E. cyaneus may support aerobic metabolism and an active lifestyle at all exposure temperatures. Rising temperatures in summer may provide a competitive advantage for G. lacustris compared to the Baikal species but the inactive lifestyle in the cold is likely preventing G. lacustris from establishing a stable population in Lake Baikal.

Polyelectrolyte microcapsules are among the most promising carriers of various sensing substances for their application inside the bloodstream of vertebrates. The long-term effects of biodegradable microcapsules in mammals are relatively well studied, but this is not the case for non-biodegradable microcapsules, which may be even more generally applicable for physiological measurements. In the current study, we introduced non-biodegradable polyelectrolyte microcapsules coated with polyethylene glycol (PMs-PEG) into the circulatory system of zebrafish to assess their long-term effects on fish internal organs with histopathologic analysis. Implantation of PMs-PEG was not associated with the formation of microclots or thrombi in thin capillaries; thus, the applied microcapsules had a low aggregation capacity. The progression of the immune response to the implant depended on the time and the abundance of microparticles in the tissues. We showed that inflammation originated from recognition and internalization of PMs-PEG by phagocytes. These microcapsule-filled immune cells have been found to migrate through the intestinal wall into the lumen, demonstrating a possible mechanism for partial microparticle elimination from fish. The observed tissue immune response to PMs-PEG was local, without a systemic effect on the fish morphology. The most pronounced chronic severe inflammatory reaction was observed near the injection site in renal parenchyma and within the abdominal cavity since PMs-PEG were administered with kidney injection. Blood clots and granulomatosis were noted at the injection site but were not found in the kidneys outside the injection site. Single microcapsules brought by blood into distal organs did not have a noticeable effect on the surrounding tissues. The severity of noted pathologies of the gills was insufficient to affect respiration. No statistically significant alterations in hepatic morphology were revealed after PMs-PEG introduction into fish body. Overall, our data demonstrate that despite they are immunogenic, non-biodegradable PMs-PEG have low potential to cause systemic effects if applied in the minimal amount necessary for detection of fluorescent signal from the microcapsules.

Proper diet is critical for laboratory-reared animals, as it may affect not only their welfare, but also experimental results. Amphipods (Crustacea: Amphipoda) play important roles in ecosystems and are often used in environmental research. Endemic amphipods from the ancient Lake Baikal are promising for laboratory bioassays; however, there are currently no laboratory cultures. In this work, we determine how different diets affect the color and metabolism of a laboratory-reared Baikal amphipod, Eulimnogammarus cyaneus. We found that in freshly collected blue-colored animals, body color correlated with total carotenoid content. Total carotenoid levels did not differ after long-term (two months) feeding with a close to natural carotenoid-enriched, or even a carotenoid-depleted diet. Nevertheless, antennae color was closer to red in the natural-like diet group. It is likely that the carotenoids from the commercial diet are not properly metabolized in E. cyaneus. The animals fed commercial diets had a higher glycogen content, which may signify a higher metabolic rate. Overall, we show that a carotenoid-enriched diet optimized for decapods is not optimal for amphipods, likely due to different carotenoid compositions, and the diet for long-term rearing of E. cyaneus and other Baikal amphipods requires supplementation.

Hemocytes are cells circulating in the hemolymph and playing an important role in crustacean immunity. These cells not only function as phagocytes but also express immune compounds to the hemolymph. Here we obtained hemocyte proteome of the endemic amphipod (Amphipoda, Crustacea) Eulimnogammarus verrucosus from Lake Baikal, the first hemocyte proteome of an amphipod, using liquid chromatography/tandem mass spectrometry (LC-MS/MS). A total of 1152 unique proteins were discovered with LC-MS/MS. We discovered both proteins directly involved in the immune response, such as pattern recognition proteins (C-type lectins), and compounds with antimicrobial activity (ctenidin and anti-lipopolysaccharide factor/scygonadin). Moreover, hemocyanins which may act as a phenoloxidase and C-type lectins were among the most diverse protein groups in the hemocyte proteome. The obtained data can be useful for further studies of immune components and mechanisms in Baikal amphipods.

В экспериментах определено влияние плотности посадки особей и температуры среды (воды) на параметры роста (длительность межлиночного периода, масса особей и прирост массы после линьки) мраморного рака Procambarus virginalis. Выявлено, что содержание раков в малых сосудах (площадь дна 5,7 см 2) негативно сказывается на их росте и в итоге приводит к гибели. Эксперимент показал, что особи P. virginalis из летней серии линяют чаще, чем из зимней. В среднем длительность межлиночного периода в зимнее время (17-20 о С) в 1,5 больше, чем в летнее (22-30 о С). При этом повышение температуры свыше 25 о С приводит к увеличению межлиночного периода. The influence of the environment temperature and the density of the landing on the growth parameters (duration of the inter-molting period, weight of individuals and weight gain after molting) of marble crayfish Procambarus virginalis in laboratory experiments have been estimated. It was revealed that the cultivation of crayfish in small vessels (bottom area 5.7 cm 2) negatively affects their growth and ultimately leads to death. The experiment showed that individuals of P. virginalis from the summer series molt more often than from the winter one. Аverage duration of the inter-molting period in winter (17-20 °C) is 1.5 times longer than the summer (22-30 °C). In this case, temperature rise over 25 °C leads to an increase in the inter-molting period.