Том 44, № 1 (2017)

The growth and morphogenesis of glochidia of the freshwater pearl mussel Margaritifera margaritifera on the gills of the Atlantic salmon Salmo salar in the Syuskyuyanyoki River (Karelia) are studied. Comparative analysis of histological features of glochidia depending on the age of the cyst is made, and the results of studies of the relationship and the influence of seasonal changes in water temperature on growth and morphogenesis of glochidia, which is essential for adaptation of living organisms and ensuring the sustainability of the participants of the parasite–host relationship, are presented.

A comparative study of the lipid status of gills of juvenile Atlantic salmon infested with glochidia of the freshwater pearl mussel inhabiting the Vuokinyoki (White Sea basin) and Syuskyuyanyoki (basin of Lake Ladoga) rivers in the fall is carried out. The most infested gills of juvenile salmon and the lower water temperature (1.3°C) in the Vuokinyoki River reveal higher cholesterol levels and cholesterol/phospholipids ratios, which are due to the influence of infection factors; thereby they slow down biochemical processes. It is noted that variations in the lipid composition in juvenile salmon the gills of which are infected with glochidia reflect the development of adaptive responses that maintain homeostasis of juveniles under invasion.

The locations and the area of the spawning–growing grounds have been assessed in the Syuskyuyanyoki River (the basin of Lake Ladoga), as has the population density of the juveniles of the freshwater form of the Atlantic salmon and the brown trout. The Atlantic salmon spawns at present on the rapids downstream of the hydroelectric power plant because of the insurmountable dam; the population density of this species has decreased dramatically. Only the landlocked form of the brown trout was found; the anadromous form was not. The brown trout has resettled along the major part of the river. We suggest that there are two subpopulations of the freshwater pearl mussel that differ with regard to the host for their larvae. The intensity of invasion of the juveniles of salmonids by the larvae of the freshwater pearl mussel and the survivability of glochidia did not depend on the host species. The growth rate of the mollusks and the age–size structure of the freshwater pearl mussel population have been assessed.

The activity of some enzymes involved in energy and carbohydrate metabolism was studied in Atlantic salmon embryos at the eyed egg stage and in salmon fingerlings (0+) from two trophic–ecological groups: the Varzuga River bed and two tributaries, the Pyatka and Sobachii rivers (Kola Peninsula). It has been demonstrated that heterogeneity of embryos was most evident in the case of cytochrome c oxidase (CO), malate dehydrogenase (MDH), glycerol-1-phosphate dehydrogenase (G1PDH), and glucose-6-phosphate dehydrogenase (G6PDH), while the lowest level of heterogeneity was observed for lactate dehydrogenase (LDH) and aldolase. A positive correlation was revealed between the activities of CO, LDH, MDH, and G1PDH. It was noted that G6PDH showed a negative correlation with almost all enzymes under study. It was found that salmon juveniles inhabiting the tributaries were characterized by high LDH, aldolase, and G1PDH activity and lower activity of G6PDH compared to the juveniles inhabiting the main river bed. Notably, the differences in the activity of the enzymes involved in aerobic metabolism between the two groups of fingerlings under analysis were observed only in the autumn.

This paper reports a study of the activity of calcium-dependent proteases (calpains) and proteasome in the skeletal muscles of parrs and smolts of the Atlantic salmon Salmo salar L. from the Indera River (the Kola Peninsula). It was demonstrated that the growth rate and protein mass accumulation during smoltification in salmonid fishes are inversely related to the activity of proteases in their muscles. It was noted that decreased protein degradation in the skeletal muscles of salmon juveniles serves as a mechanism ensuring the intensive growth and physiological maturity necessary for migration from the river to the sea.

Endangered freshwater pearl mussels Margaritifera margaritifera reveal a complex life cycle with an obligate host-dependent phase. Only two species, Atlantic salmon Salmo salar and brown trout S. trutta, are important hosts in Europe, indicating a high degree of specialization. Whilst freshwater pearl mussels with their filtering activity can provide important ecosystem services and indirectly improve the habitat quality for their salmonid hosts, their direct effects on physiological stress, reduced swimming performance, and increased mortality at high rates of infestation all support a parasitic character of the mussel during its hostdependent phase. From an evolutionary perspective, both the much greater generation time of the parasite compared to the host, as well as the great distribution ranges of M. margaritifera and its hosts should favour local adaptation patterns. The variable suitability of different salmonid strains and species as hosts for M. margaritifera and the resulting differences in the performance of larvae during the host-dependent phase indicate that host-management strategies should focus on maintaining high quality hosts at a regional scale to avoid selection or genetic drift effects which could erode the genetic and evolutionary potential for adaptation to changing environmental conditions.

Information on the present distribution and status of the threatened freshwater pearl mussel Margaritifera margaritifera populations in Finland was updated. The status of the populations was classified into seven categories which are viable, maybe viable, non-viable/partly viable, dying-out, almost extinct, probably extinct, and extinct. The main criteria for judging the viability class were the population size and proportion of juvenile mussels. According to calculated estimate 1.7% populations were viable, 8.5% maybe viable, 40.2% non-viable/partly viable, 14.5% dying-out, 30.8% almost extinct, and 4.3% probably extinct. The present number of rivers with M. margaritifera in Finland is 117.

The populations of two endangered species—the freshwater pearl mussel Margaritifera margaritifera and the thick shelled river mussel Unio crassus in Latvia were studied. The specimens were counted, measured, population density and age structure were calculated. The possible host fish presence was found.