Characterization of feeding and downstream migration of juvenile chum salmon in the Kichiga river (north-eastern kamchatka)

Analysis of the data of fish biology spring-summer researches in the Kichiga river basin in the period 2017–2019 for the first time brought results as next: characterized dynamics of chum salmon juvenile downstrean migration, including daily dynamics, revealed qualitative characteristics of the underyearlings, described diet of the juvenile migrants, demonstrated effects of the spring-summer hydrological regime on the intensity of the underyearling feeding. Also noted, that the conditions for the downstream migration of chum salmon in 2018 were maximum favouravle, and most likely that could enhance later juvenile survival.

A Confocal Microscopic Study of Gene Transfer into the Mesencephalic Tegmentum of Juvenile Chum Salmon, Oncorhynchus keta, Using Mouse Adeno-Associated Viral Vectors

To date, data on the presence of adenoviral receptors in fish are very limited. In the present work, we used mouse recombinant adeno-associated viral vectors (rAAV) with a calcium indicator of the latest generation GCaMP6m that are usually applied for the dorsal hippocampus of mice but were not previously used for gene delivery into fish brain. The aim of our work was to study the feasibility of transduction of rAAV in the mouse hippocampus into brain cells of juvenile chum salmon and subsequent determination of the phenotype of rAAV-labeled cells by confocal laser scanning microscopy (CLSM). Delivery of the gene in vivo was carried out by intracranial injection of a GCaMP6m-GFP-containing vector directly into the mesencephalic tegmentum region of juvenile (one-year-old) chum salmon, Oncorhynchus keta. AAV incorporation into brain cells of the juvenile chum salmon was assessed at 1 week after a single injection of the vector. AAV expression in various areas of the thalamus, pretectum, posterior-tuberal region, postcommissural region, medial and lateral regions of the tegmentum, and mesencephalic reticular formation of juvenile O. keta was evaluated using CLSM followed by immunohistochemical analysis of the localization of the neuron-specific calcium binding protein HuCD in combination with nuclear staining with DAPI. The results of the analysis showed partial colocalization of cells expressing GCaMP6m-GFP with red fluorescent HuCD protein. Thus, cells of the thalamus, posterior tuberal region, mesencephalic tegmentum, cells of the accessory visual system, mesencephalic reticular formation, hypothalamus, and postcommissural region of the mesencephalon of juvenile chum salmon expressing GCaMP6m-GFP were attributed to the neuron-specific line of chum salmon brain cells, which indicates the ability of hippocampal mammal rAAV to integrate into neurons of the central nervous system of fish with subsequent expression of viral proteins, which obviously indicates the neuronal expression of a mammalian adenoviral receptor homolog by juvenile chum salmon neurons.

Long-term trends in distribution and regional composition of the catches of hatchery pink and chum salmon during autumn migrations in the basin of the Sea of Okhotsk

Long-term trends in distribution and regional composition of the catches of hatchery pink and chum salmon during autumn post-catadromous migrations in the basin of the Sea of Okhotsk in 2011–2017 were evaluated based on the otolith marking data. Qualitative and intraspecific structure of the hatchery fish aggregations was analyzed in connection to the interannual variety in forming abundant and not abundant generations of pink salmon. The analyze is carried out allowed to find out that the aggregation density of Russian and Japan hatchery juvenile chum salmon in the eastern part of the Sea of Okhotsk is higher in the even years of observation. Along that the distribution of the active migrants of the Sakhalin-Kurile and Hokkaido stock complexes in the north-east direction withing the Okhotsk Sea basin is better expressed. We think, that the main reason is low abundance of pink salmon generations (odd years of spawning) on West Kamchatka during autumn migration in the even years.In general the results obtained indicate that the cyclic migration of juvenile pink and chum salmon in the basin of the Sea of Okhotsk during post-catadromous migrations is of a systemic and mass character. Hatchery and wild fish have been engaged. The scheme of the juvenile distribution is similar in even and odd years.