E. A. Kirillova

Lipid status and feeding habits of salmonid juveniles in the year preceding seaward migration as factors controlling their future smoltification

Juveniles of coho salmon Oncorhynchus kisutch (Walb.) and mykiss Parasalmo mykiss (Walbaum) of the same age (1+) become differentiated as early as eight months before smoltification and seaward migration by their lipid level, feeding habits, and size and weight parameters. It is found that juveniles of coho salmon and mykiss with a high lipid status have a greater (on average) length and weight and consume more calorific food items. The juveniles with a lower lipid status have a lower length and weight and consume less calorific organisms. It is presumed that a considerable part of juveniles with a high lipid status will migrate seaward next year. The role of the trophic factor in development of this differentiation and, accordingly, in determination of smoltification dates is discussed.

Downstream migration in ammocoetes of the Arctic lamprey Lethenteron camtschaticum in some Kamchatka rivers

This paper considers the major patterns of downstream migration in Arctic lamprey ammocoetes in Kamchatka rivers. Ammocoetes of different age groups are shown to be constantly noted in the composition of the migrant part of a river community. The greatest intensity of downstream migration in ammocoetes of the age class 0+ is noted in the period of their primary dispersion in late July-early August. The ammocoetes of the age groups 1+ and older migrate from spring to late autumn, but their concentrations are not high. The significant similarity of such a biologic feature as downstream migration in ammocoetes and juvenile salmonids serves as an example of ecological analogy.

Patterns and some mechanisms of downstream migration of juvenile salmonids (with reference to the Utkholok and Kalkaveyem Rivers in Northwestern Kamchatka)

Principal patterns of the downstream migration of juvenile salmonids (Salmonidae) were discovered on the basis of data of three years of observations. It was found that the time of the beginning, the duration, and the scope of the downstream migration in each particular year are determined by a complex of environmental factors. The crucial abiotic factors are the temperature, the water level of the river, and the illumination. The biotic factors comprise the complex trophic factor. The abiotic environmental factors play the leading role in the realization of the downstream migration at the early ontogenetic stages. The role of the biotic environmental factors increases at the late ontogenetic stages. It was demonstrated that the juveniles that perform downstream migrations are a heterogeneous group consisting of fish of different species and specimens at different ontogenetic stages, of various sizes and ages, and those ready for the transition to the marine environment to variable degrees. The analysis of the patterns of the downstream migration allowed us to describe some mechanisms that control the realization of this process.

The lipid status of young of the year mykiss Parasalmo mykiss and coho salmon Oncorhynchus kisutch

The young of the year mykiss Parasalmo mykiss and coho salmon Oncorhynchus kisutch which perform downstream migration and which stay in the coastal zone during the period of primary dispersion represent different phenotypic groups. They differ in weight, length, and lipid status. Such differentiation is a factor controlling the formation of intrapopulation diversity and of the life strategy of fish. It may determine the timing of smoltification in the future and, further on, of the return for spawning. There were found some analogies and differences in characteristics of lipid metabolism in the investigated species. The content of total lipids decreases by autumn in underyearlings of both species. Furthermore, changes in the content of particular lipid fractions are multidirectional and various scaled, seemingly being related to physiological preparation for the wintering.

Lipid content in the young-of-the-year sockeye salmon Oncorhynchus nerka during feeding migration (the Ozernaya River, Western Kamchatka)

235 Sockeye salmon Oncorhynchus nerka of Kam� chatka populations in comparison to other Pacific salmon differs in that it spends its freshwater period predominantly in lakes. Spawning grounds of sockeye salmon are situated both in lakes and in rivers flowing in or out of the lakes. Therefore, to reach a rearing lake juvenile sockeye salmon perform differently directed migrations as soon as in the first year of life. The direc� tion of migrations depends on the location of spawn� ing areas relative to the rearing lake. Before the escape to the lake youngoftheyear sockeye salmon accu� mulate in the river source in the zone of reverse flow (5, 6). Along with mass upstream migration, down� stream migration occurs in rivers flowing out of lakes (6, 7, 13). The youngoftheyear of sockeye salmon per� forming upstream and downstream migrations and those preparing for escape to the lake differ in body length, behavior, and feeding patterns. On the basis of these characteristics, they could be assigned to differ� ent phenotypic groups (6, 7). There are data on physi� ological and biochemical differentiation in the fish performing upstream and downstream migrations: Patterson et al. and Pon et al. (14, 15) demonstrated that the fry performing differently directed feeding migrations differ in swimming performance and in the content of oxidative enzymes. Depending on the direction, migrations may require considerable energy expenditures and there� fore may be accompanied by restructuring at the cellu� lar level, which are provided by lipids to a considerable extent. Individual classes of lipids perform various functions in the body. Each of these functions has a determinative significance in a certain ecological- physiological situation (10). Therefore, lipids are a major index of biochemical differentiation. This determined the aim of the present study, namely, com� parative analysis of the content of lipids in sockeye salmon juveniles of the first year of life from different phenotypic groups in the period of feeding migration, in order to confirm the presence of these groups at the physiological-biochemical level.

The lipid status and feeding habits of yearlings of mykiss Parasalmo mykiss and coho salmon Oncorhynchus kisutch in autumn

Juveniles of coho salmon Oncorhynchus kisutch and mykiss Parasalmo mykiss at the age 1 + (yearlings) are differentiated by the content of different fractions of lipids (the lipid status), feeding habits, and by size-weight characteristics even eight months prior to smoltification. The juveniles of coho salmon and mykiss with high lipid status consume more calorific food items and, as a rule, have higher (on average) body length and weight. The juveniles with low lipid status consume less calorific organisms and have lower body length and weight. It is supposed that a considerable part of juveniles with high lipid status will migrate seaward the next year. The role of feeding habits in formation of this differentiation and, accordingly, in determination of timing of smoltification are discussed.

Migration of Young of the Year of Dolly Varden Char Salvelinus malma (Walbaum) from the Spawning Tributary in the Basin of Lake Kuril'skoye (Southern Kamchatka)

The downstream migration of young of the year Dolly Varden char Salvelinus malma from the spawning tributary of Lake Kuril’skoye has been studied. It is demonstrated that this migration is an essential stage in the life cycle of this species. Both alevins and fry of Dolly Varden char perform the first feeding migration. It lasts for about 1 month in the examined creek, from early June to mid-July. The migration comes to an end when the sockeye salmon begin spawning in the creeek. Clear diurnal dynamics is inherent for the migration: it occurs only in the dark time of the day. The mass migration from the creek is caused by the deficiencies of habitats and unfavorable feeding conditions.

Downstream migration of fry of pink salmon Oncorhynchus gorbuscha (Walbaum) in the Malaya Huzi River (Northeastern Sakhalin)

Patterns of downstream migration in pink salmon fry are investigated; data on migration time, its seasonal and daily dynamics, morphobiological characteristics of fry, and total number of migrants are obtained. Behavioral features of fry during the migration both in the main stream and in the estuary of the river are studied. Mechanisms of fry distribution in the flow and its connection with hydraulic structure of the flow and active behavioral elements are revealed. A comparison of two alternative methods for quantitative assessment of downstream migrants has proved the efficiency of both of them.

Downstream migration, behavior, and distribution of fish fry in the lower reaches of the Ozernaya river (Southwestern Kamchatka)

Fry of five species of salmonids are found in the lower reaches of the Ozernaya River. The most abundant are chum salmon and pink salmon which compose the bulk of fry which migrate downstream from the river to the sea. The dates and duration of migration of particular species differed according to the specific traits of their biology. Pink salmon is characterized by a simple migration strategy: it migrated downstream in a short time after emergence from the ground. Chum salmon has two strategies of downstream migration: some fry start migration soon after emergence, and others remained in the river for several weeks. Downstream migration of pink salmon occurred mainly at night in contrast to that of chum salmon, over 24 h, the part of daytime increased with growth of the fish. Migration of pink salmon was passive. Passive migration of chum salmon changed into active-passive with growth of the fish. The ratio of fish in the inshore zone and in the current was different in the course of 24 h. The number of fish in the inshore zone decreased in the period of intensive downstream migration.

Morpho-ecological patterns and feeding of coho salmon Oncorhynchus kisutch fry in the period of downstream migration

The principal patterns of feeding of downstream-migrant and coastal young of the year of coho salmon are considered. The so-called potential downstream migrants and residents, which differ in size and feeding patterns, were distinguished among coastal fry. It is assumed that identification of particular coastal specimens to phenotypic groups of downstream migrants or nonmigrants of young of the year of coho salmon may be determined even in the daytime by such parameters as the body length, feeding intensity, and food spectrum.