Evolutionary-physiological aspects of adaptation of the Pacific salmon fry of the oncorhynchus genus to migration to the sea water

A complex of adaptive changes occurring in the Pacific salmon fry in the process of migration to the sea is described, including behavior, ion content in carcasses, and morphological changes in Stannius bodies, gill epithelium, and nephron tubular epithelium. Participating in experiments with transfer from fresh water into a two-layer aquarium (the lower layer—sea water, the upper layer—fresh water) were smolts of chum salmon and underyearlings of cherry salmon as well as the trachurus and leiurus forms of the three-spined stickleback Casterosteus aculeatus. All fish, regardless of their salt preference, at once after placement into the two-layer aquarium, occupied the sea water zone, at the very bottom of the aquarium. After 1 h, there started brief excursions of cherry salmon and chum salmon to the upper, fresh water layer; however, both forms of the three-spined stickleback did not participate in these excursions. After 12 h, the chum salmon settled down in the lower, sea water layer, while the cherry salmon—in the upper, fresh water layer. Both forms of the three-spined stickleback never left the sea water layer and felt quite comfortably on the aquarium bottom. It seems that the high tolerance of the both stickleback forms to wide salinity limits allows them to choose the convenient position regardless of the water salt composition. By analyzing the material obtained for three years (2001–2003) on structure and functions of the gill epithelium chloride cells (CC), we have come to the conclusion that the fresh water fry of two salmon species, chum and cherry salmons, caught at the same time and practically in the same water reservoirs can be divided into three groups. The underyearlings of the cherry salmon as a rule are characterized by the thickened epithelium of secondary gill lamellae, but by a very small number of CC. In smolts of chum salmon, on the contrary, the epithelium is sufficiently thin, but enriched in the CC that demonstrate an active structure in the very beginning of migration to sea. However, with approaching the sea (and with an increase of terms of migration) the CC activity drops, but their amount does not change. And only after migration to the sea the CC activity rises again, although their amount seems to remain unchanged. The described peculiarities of behavior and of the ion composition regulation in the migrating salmon fry confirm the hypothesis that the salmons evolutionized in fresh water, that the Oncorhynchus genus appeared in large spaces of saltish waters, such as the Japan sea at the period of the early Pleistocene, and that learning of fry of the Oncorhynchus genus (for instance, of O. gorbuscha and O. keta) is the most specialized in the salmons migration to the sea, whereas the fresh water species of chars (Salvelinus) and of trouts (Salmo) are more primitive.     

Preferences of invasive Ponto-Caspian and native European gammarids for zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>, Bivalvia) shell habitat

The migratory behavior and swimming patterns of anadromous upstream migratory fish have been poorly described in the Shibetsu River in eastern Hokkaido, Japan. In this 2004 study, we used electromyogram (EMG) transmitters and depth/ temperature (DT) loggers to compare the upstream migratory behavior of adult male chum salmon (Oncorhynchus keta) and pink salmon (O. gorbuscha) in the canalized and reconstructed segments of the Shibetsu River, where a part of canalized section was preliminary reconstructed meander to restore a more natural section. The EMG transmitter and DT logger were externally attached to the left side of the body, below the front edge of the dorsal fin. Fish of both species often migrated along the riverbanks and near the bottom of the water column, sometimes engaged in holding behavior, which was defined as cessation of swimming during their upstream migration for 5 minutes. Modal swimming depth calculated by DT loggers for chum salmon (0.2–0.4 m) was shallower than pink salmon (0.6–0.8 m). Further, modal swimming speeds measured by calibrated EMG for chum salmon (0.2–0.4 BL s⁻¹) were slower than pink salmon (1.2–1.4 BL s⁻¹). Pink salmon swam faster as well as in relatively deeper than chum salmon, suggesting that they expend more energy than chum salmon in the reconstructed segment. Based on these results, it seemed likely that the upstream migration behavior of chum and pink salmon was different with species-specific strategies.     

Agonistic behavior in a schooling fish: form,function and ontogeny

Synopsis Although juvenile chum salmon,Oncorhynchus keta, are generally regarded as a schooling fish, when presented with a defensible point-source of food, some individuals abandon schooling, aggressively subordinate competitors, and monopolize food. When food is removed, fish gradually abandon solitary agonistic behaviors and return to schooling behavior. Agonism increases in frequency and intensity as juveniles age. The ability to alternate facultatively between schooling and solitary agonistic behavior may enable juvenile chum to respond to local patterns of food distribution and predation risk. The ontogenetic increase in agonism may result in school dispersal as fish move from the estuary into coastal waters, and may well reflect a shift in the costs versus the benefits of schooling as fish mature and become less vulnerable to predation.     

Riverine movements of hatchery-reared Atlantic salmon (Salmo salar) upon return as adults

Synopsis Hatchery-reared Atlantic salmon returning as adults to Maine's Penobscot River drainage basin were tagged with radio transmitters to permit long-term observation of their movements. Locations of salmon carrying small stomachemplaced transmitters were periodically determined primarily from an airplane; canoes and road vehicles were also used. Objectives were to determine the patterns, routes and rates of salmon movement; to assess the effect of dams on the migration; and to compare the behavior of salmon that had been imprinted as smolts to headwaters with that of salmon released as smolts near the head of tide. No consistent pattern of salmon movement emerged. Movement was erratic with wandering both up and downstream interspersed with position holding. A weak seasonal aspect to the movement was detected, with the minimum numbers moving in early September and the rates and distances of movement decreasing as the season progressed. Salmon often remained at various locations in the rivers for periods of time before subsequently moving. Salmon were also apparently impeded by dams, as on numerous occasions they were observed to approach a dam, then move back downstream. Some differences in behavior were found between the salmon imprinted as smolts to headwaters and those released as smolts at head of tide. Several imprinted salmon homed to a particular tributary when unimpeded by dams or homed by surmounting a dam, and several moved up to the base of the dam. Few unimprinted salmon moved up that tributary. The variable behavior and lack of strong upstream movement may be due to the salmon's lack of genome adapted to the Penobscot River drainage, the scarcity of conspecifics with their possible pheromonal influence, and the lack of a home stream and concomitant motivation to stimulate unimprinted salmon to progress upstream.     

Variability in Migration Routes Influences Early Marine Survival of Juvenile Salmon Smolts

Variability in animal migratory behavior is expected to influence fitness, but few empirical examples demonstrating this relationship exist. The initial marine phase in the migration of juvenile salmon smolts has been identified as a potentially critical life history stage to overall population productivity, yet how fine-scale migration routes may influence survival are unknown. Large-scale acoustic telemetry studies have estimated survival rates of outmigrant Pacific salmon smolts through the Strait of Georgia (SOG) along the British Columbian coastline to the Pacific Ocean, but these data have not been used to identify and characterize fine-scale movements. Data collected on over 850 sockeye salmon (Oncorhynchus nerka) and steelhead (Oncorhynchus mykiss) smolts detected at an array in the Strait of Georgia in 2004–2008 and 2010–2013 were analyzed to characterize migration routes and link movements to subsequent survival at an array 250 km further along the marine migration pathway. Both species exhibited disproportionate use of the most eastern route in the Strait of Georgia (Malaspina Strait). While many smolts moved across the northern Strait of Georgia acoustic array with no indication of long-term milling or large-scale east-to-west movements, large proportions (20–40% of sockeye and 30–50% of steelhead) exhibited a different behavior, apparently moving in a westward or counterclockwise pattern. Variability in migratory behavior for both species was linked to subsequent survival through the Strait of Georgia. Survival for both species was influenced by initial east-to-west location, and sockeye were further influenced by migration timing and duration of time spent near the northern Strait of Georgia array. Westward movements result in a net transport of smolts from Malaspina Strait to the Strait of Georgia, particularly for steelhead. Counterclockwise movements may be due to the currents in this area during the time of outmigration, and the higher proportion of steelhead smolts exhibiting this counterclockwise behavior may reflect a greater exposure to wind-altered currents for the more surface-oriented steelhead. Our results provide an empirical example of how movements can affect migration survival, for which examples remain rare in movement ecology, confirming that variability in movements themselves are an important part of the migratory process.     

Food spectra of the farm juveniles of the Chum Salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> (Salmoniformes,Salmonidae) in the Ryazanovka River (Southern Primor’e)

Qualitative data are presented on the diet of juvenile chum salmon Oncorhynchus keta released from the Ryazanovka experimental fish hatchery farm situated in the south of Primor’e Territory. The stomach fullness, frequency of occurrence of food items, their average weight value, and selectivity are estimated. Food spectra of chum salmon juveniles during downstream migration comprised representatives of 51 taxa of bottom freshwater invertebrates and terrestrial insects. The bulk of the diet consisted of larvae of aquatic insects—chironomids, other Diptera, and mayflies. Their diversity increased with the growth of fry. Fry of chum salmon had a wide spectrum of feeding preference, favorite food items were larvae and pupae of chironomids.     

Temporal differentiation and conditions of reproduction of chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> (Salmoniformes,Salmonidae) from the Tugur River basin (Khabarovsk Krai)

Chum salmon Oncorhynchus keta from the Tugur River of Khabarovsk krai was studied. It was found that, in the river basin, chum salmon of two ecological groups reproduces: the first spawns at river sections with a pronounced underflow and the second spawns at river sections with a groundwater outlet. In the first anadromous migration, usually three maxima of the number of approaches of migrating fish are observed. The first in time maximum is represented by early (or summer) chum salmon, the second includes migrants of early and late (or autumn) form, and the third is represented by chum salmon of only late form. Forms of chum salmon from the Tugur River basin different in dates of the run and the spawning sites differ not only in the ecology of reproduction but also in biological indices. The later chum salmon is larger; its gonads at entry into the river for spawning are less mature as compared with early chum salmon. The autumn form of chum salmon reproducing at key spawning grounds is distributed more widely than the summer form. It is found along the Asian coast from Chukotka in the north to Japan and Korea in the south. Summer chum salmon occupies only part of the range of the autumn form.     

Evolutionary-physiological aspects of adaptation of the Pacific salmon fry of the Oncorhynchus genus to migration to the sea water

A complex of adaptive changes occurring in the Pacific salmon fry in the process of migration to the sea is described, including behavior, ion content in carcasses, and morphological changes in Stannius bodies, gill epithelium, and nephron tubular epithelium. Participating in experiments with transfer from fresh water into a two-layer aquarium (the lower layer - sea water, the upper layer - fresh water) were smolts of chum salmon and underyearlings of masu salmon as well as the trachurus and leiurus forms of the three-spined stickleback Casterosteus aculeatus. All fish, regardless of their salt preference, at once after placement into the two-layer aquarium, occupied the sea water zone, at the very bottom of the aquarium. After 1 h, there started brief excursions of masu salmon and chum salmon to the upper, fresh water layer; however, both forms of the three-spined stickleback did not participate in these excursions. After 12 h, the chum salmon settled down in the lower, sea water layer, while the masu salmon - in the upper, fresh water layer. Both forms of the three-spined stickleback never left the sea water layer and felt quite comfortably on the aquarium bottom. It seems that the high tolerance of the both stickleback forms to wide salinity limits allows them to choose the convenient position regardless of the water salt composition. By analyzing the material obtained for three years (2001-2003) on structure and functions of the gill epithelium chloride cells (CC), we have come to the conclusion that the fresh water fry of two salmon species, chum and masu salmons, caught at the same time and practically in the same water reservoirs can be divided into three groups. The underyearlings of the masu salmon as a rule are characterized by the thickened epithelium of secondary gill lamellae, but by a very small number of CC. In smolts of chum salmon, on the contrary, the epithelium is sufficiently thin, but enriched in the CC that demonstrate an active structure in the very beginning of migration to sea. However, with approaching the sea (and with an increase of terms of migration) the CC activity drops, but their amount does not change. And only after migration to the sea the CC activity rises again, although their amount seems to remain unchanged. The described peculiarities of behavior and of the ion composition regulation in the migrating salmon fry confirm the hypothesis that the salmons evolutionized in fresh water, that the Oncorhynchus genus appeared in large spaces of saltish waters, such as the Japan Sea at the period of the early Pleistocene, and that learning of fry of the Oncorhynchus genus (for instance, of O. gorbuscha and O. keta) is the most specialized in the salmons migrating to the sea, whereas the fresh water species of chars (Salvelinus) and of trouts (Salmo) are more primitive.     

Growth hormone-releasing hormone and corticotropin-releasing hormone enhance non-rapid-eye-movement sleep after sleep deprivation

The neuropeptides growth hormone (GH)-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) regulate sleep and nocturnal hormone secretion in a reciprocal fashion, at least in males. GHRH promotes sleep and GH and inhibits hypothalamo-pituitary-adrenocortical (HPA) hormones. CRH exerts opposite effects. In women, a sexual dimorphism was found because GHRH impairs sleep and stimulates HPA hormones. Sleep deprivation (SD) is the most powerful stimulus for inducing sleep. Studies in rodents show a key role of GHRH in sleep promotion after SD. The effects of GHRH and CRH on sleep-endocrine activity during the recovery night after SD are unknown. We compared sleep EEG, GH, and cortisol secretion between nights before and after 40 h of SD in 48 normal women and men aged 19-67 yr. During the recovery night, GHRH, CRH, or placebo were injected repetitively. After placebo during the recovery night, non-rapid-eye-movement sleep (NREMS) and rapid-eye-movement sleep (REMS) increased and wakefulness decreased compared with the baseline night. After GHRH, the increase of NREMS and the decrease of wakefulness were more distinct than after placebo. Also, after CRH, NREMS increased higher than after placebo, and a positive correlation was found between age and the baseline-related increase of slow-wave sleep. REMS increased after placebo and after GHRH, but not after CRH. EEG spectral analysis showed increases in the lower frequencies and decreases in the higher frequencies during NREMS after each of the treatments. Cortisol and GH did not differ between baseline and recovery nights after placebo. After GHRH, GH increased and cortisol decreased. Cortisol increased after CRH. No sex differences were found in these changes. Our data suggest that GHRH and CRH augment NREMS promotion after SD. Marked differences appear to exist in peptidergic sleep regulation between spontaneous and recovery sleep.     

Gonadal steroid regulation of pineal melatonin synthesis.

The regulation of gonadal function by the vertebrate pineal, primarily through the biological actions of melatonin has received much attention from investigators during the past decade (1–5). Melatonin is synthesized from serotonin through the activities of the pineal enzymes N-acetyl transferase (NAT) and hydroxyindole-O-methyl transferase (HIOMT). NAT converts serotonin to N-acetyl serotonin by coupling of the acetyl function from Acetyl Coenzyme A to serotonin. HIOMT transfers the methyl group from S-adenosylmethionine to N-acetyl serotonin, to form melatonin.     

The involvement of sex steroid hormones in downstream and upstream migratory behavior of masu salmon

From May through July when masu salmon, Oncorhynchus masou, commence downstream migration under natural conditions, yearling precocious male masu salmon (resident form) showed higher GSI and plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) in contrast to immature smolts (migratory form). From March through September coinciding with the upstream migration period, 2-year-old male and female adults also showed higher GSI and plasma levels of T, estradiol-17beta (E(2)) 11-KT, 17alpha-hydroxyprogesterone and 17alpha,20beta-dihydroxy-4-pregnene-3-one (DHP). In order to test the effects of steroid hormones on migratory behaviors, silascone tube capsules containing 500 microg of T, E(2), 11-KT, DHP, or a vehicle was implanted into smolts, castrated precocious males, or immature parr, and downstream and upstream behavior were observed in artificial raceways in spring and autumn. Downstream behavior of smolts was inhibited significantly by T, E(2) and 11-KT. Upstream behavior was stimulated by T and 11-KT in castrated precocious males and stimulated by T, E(2) and 11-KT in immature parr. These results indicate that T, E(2) and 11-KT are the factors regulating downstream and upstream migratory behavior. In particular, because of its changing patterns in plasma and significant effects, T, the common precursor hormone of E(2) (female) and 11-KT (male), is considered to play central roles in both types of behavior.     

Effect of hypo-osmotic environmental changes on the expression of gonadotropin-releasing hormone,its receptor,and gonadotropin hormone subunit mRNA in adult chum salmon (Oncorhynchus keta)

Migrating fish such as salmonids are affected by external environmental factors and salinity changes are particularly important, influencing spawning migration. The aim of this study was to test whether changes in salinity would affect the expression of the hypothalamic-pituitary-gonadal (HPG) axis hormones (gonadotropin-releasing hormones (GnRHs) [salmon GnRH and chicken GnRH-II], GnRH receptors [GnRHR1 and GnRHR5], and mRNA of the gonadotropin hormone [GTH] subunits [GTHα, follicle stimulating hormone β, and luteinizing hormone β]) in chum salmon (Oncorhynchus keta). Fish were progressively transferred from seawater (SW) through 50% SW to freshwater (FW), and the relationship between the osmoregulatory hormone prolactin (PRL) and sexual maturation was determined. The expression and activity of HPG hormones and their receptors, and levels of estradiol-17β and PRL increased after fish were transferred to FW, demonstrating that changes in salinity stimulate the HPG axis and PRL production in migrating chum salmon. These findings reveal details about the role of the endocrine system in maintaining homeostasis and stimulating sexual maturation and reproduction in response to salinity changes in this species.     

睡眠中间断低氧对大鼠下丘脑-垂体-肾上腺轴和生长激素的影响

目的:探讨睡眠中间断低氧对大鼠下丘脑-垂体-肾上腺轴和生长激素水平的影响.方法:大鼠分别给予吸入空气,持续低氧和间断低氧气体,在1 d,3 d,7 d和30 d后测定下丘脑促肾上腺皮质激素释放激素(CRH)和生长激素释放激素(GHRH)mRNA水平,并测定30d后血浆CRH,GHRH,促肾上腺皮质激素(ACTH)和皮质酮水平,分析其间的变化关系.结果:与对照组比较,在低氧后1 d,3 d,7 d后大鼠下丘脑CRH mRNA升高,GHRH mRNA降低,在30 d后,间断低氧组下丘脑CRH mRNA升高,GHRH mRNA降低,而持续低氧组则接近正常.间断低氧30 d后,血浆CRH、ACTH,皮质酮均升高,GHRH降低,而生长激素没有明显变化.结论:大鼠睡眠中慢性间断低氧可以引起下丘脑-垂体-肾上腺轴激素水平升高,反馈调节紊乱,可引起GHRH分泌抑制.     

Physiological mechanisms of imprinting and homing migration in Pacific salmon Oncorhynchus spp

After several years of feeding at sea, salmonids have an amazing ability to migrate long distances from the open ocean to their natal stream to spawn. Three different research approaches from behavioural to molecular biological studies have been used to elucidate the physiological mechanisms underpinning salmonid imprinting and homing migration. The study was based on four anadromous Pacific salmon Oncorhynchus spp., pink salmon Oncorhynchus gorbuscha, chum salmon Oncorhynchus keta, sockeye salmon Oncorhynchus nerka and masu salmon Oncorhynchus masou, migrating from the North Pacific Ocean to the coast of Hokkaido, Japan, as well as lacustrine O. nerka and O. masou in Lake Toya, Hokkaido, where the lake serves as the model oceanic system. Behavioural studies using biotelemetry techniques showed swimming profiles from the Bering Sea to the coast of Hokkaido in O. keta as well as homing behaviours of lacustrine O. nerka and O. masou in Lake Toya. Endocrinological studies on hormone profiles in the brain-pituitary-gonad axis of O. keta, and lacustrine O. nerka identified the hormonal changes during homing migration. Neurophysiological studies revealed crucial roles of olfactory functions on imprinting and homing during downstream and upstream migration, respectively. These findings are discussed in relation to the physiological mechanisms of imprinting and homing migration in anadromous and lacustrine salmonids.     

Growth hormone-releasing hormone facilitates hypoglycemia-induced release of cortisol

Early sleep in humans is characterized by a distinct suppression of pituitary-adrenal activity coinciding with enhanced activity of the somatotropic axis. Here, we tested in awake humans the hypothesis of an inhibiting influence of hypothalamic growth hormone-releasing hormone (GHRH) on pituitary-adrenal activity. For this purpose, pituitary-adrenal activity was stimulated in 10 men through a standard insulin-hypoglycemia-test (IHT) and in another 10 men through combined administration of CRH/vasopressin. Stimulation was performed in each man on three conditions following pretreatment with Placebo and GHRH administered intravenously (50 microg) or intranasally (300 microg) 1 h before. GH, ACTH and cortisol as well as blood pressure and heart rate were measured repeatedly. Contrary to expectations, pretreatment with GHRH did not suppress but enhanced secretion of cortisol upon insulin-induced hypoglycemia regardless of the route of GHRH pretreatment (p<0.05). In contrast, GHRH did not facilitate cortisol release after stimulation with CRH/vasopressin. Changes in ACTH remained inconsistent. Plasma levels of GH increased significantly after i.v. GHRH application, but remained unchanged after the intranasal administration. Blood pressure and heart rate were not influenced by the treatments. Results indicate facilitating effects of GHRH mediated at a suprapituitary (i.e. hypothalamic) level as suggested by restriction of the effect to the hypoglycemia-induced cortisol release with no effects after pituitary stimulation with CRH/vasopressin.     

Elevation of gene expression for salmon gonadotropin-releasing hormone in discrete brain loci of prespawning chum salmon during upstream migration

Our previous studies suggested that salmon gonadotropin-releasing hormone (sGnRH) neurons regulate both final maturation and migratory behavior in homing salmonids. Activation of sGnRH neurons can occur during upstream migration. We therefore examined expression of genes encoding the precursors of sGnRH, sGnRH-I, and sGnRH-II, in discrete forebrain loci of prespawning chum salmon, Oncorhynchus keta. Fish were captured from 1997 through 1999 along their homing pathway: coastal areas, a midway of the river, 4 km downstream of the natal hatchery, and the hatchery. Amounts of sGnRH mRNAs in fresh frozen sections including the olfactory bulb (OB), terminal nerve (TN), ventral telencephalon (VT), nucleus preopticus parvocellularis anterioris (PPa), and nucleus preopticus magnocellularis (PM) were determined by quantitative real-time polymerase chain reactions. The amounts of sGnRH-II mRNA were higher than those of sGnRH-I mRNA, while they showed similar changes during upstream migration. In the OB and TN, the amounts of sGnRH mRNAs elevated from the coast to the natal hatchery. In the VT and PPa, they elevated along with the progress of final maturation. Such elevation was also observed in the rostroventral, middle, and dorsocaudal parts of the PM. The amounts of gonadotropin IIbeta and somatolactin mRNAs in the pituitary also increased consistently with the elevation of gene expression for sGnRH. These results, in combination with lines of previous evidence, indicate that sGnRH neurons are activated in almost all the forebrain loci during the last phases of spawning migration, resulting in coordination of final gonadal maturation and migratory behavior to the spawning ground.     

Isolation and characterization of a novel growth hormone cDNA from chum salmon (Oncorhynchus keta)

A cDNA clone which codes for a novel growth hormone has been isolated from the library of chum salmon pituitaries. The clone encodes a polypeptide of 210 amino-acid residues including 22 amino-acid residues of signal peptide, which is identical in length with known chum salmon growth hormone. In the coding region, there are 30 base substitutions, some of which result in 12 amino-acid substitutions. There are 8 base changes in the 5' untranslated region, and large insertions/deletions are in the 3' non-coding region. These results clearly indicate that there are at least two species of mRNAs for growth hormone in chum salmon pituitary.     

Interaction between hatchery and wild Pacific salmon in the Far East of Russia: A review

We review studies of interactions between hatchery and wild Pacific salmon in the Russian Far East. This includes the role of hatchery practices that result in premature migration to the sea and increased mortality, and data on feeding and territorial competition between juveniles of hatchery and wild origin. In the course of downstream migration many juvenile hatchery salmon are eliminated by wild salmon predation. During the marine period, Japanese hatchery chum salmon (Oncorhynchus keta) distribution overlaps the distribution of Russian wild salmon. Consequently, replacement of wild populations by hatchery fishes, as a result of abundant juvenile hatchery releases combined with extensive poaching in spawning grounds, is apparent in some Russian rivers. Interactions between the populations occur in all habitats. The importance of conservation of wild salmon populations requires a more detailed study of the consequences of interactions between natural and artificially reared fishes.     

Adaptive strategies and life history characteristics in a warming climate: Salmon in the Arctic?

In the warming Arctic, aquatic habitats are in flux and salmon are exploring their options. Adult Pacific salmon, including sockeye (Oncorhynchus nerka), coho (O. kisutch), Chinook (O. tshawytscha), pink (O. gorbuscha) and chum (O. keta) have been captured throughout the Arctic. Pink and chum salmon are the most common species found in the Arctic today. These species are less dependent on freshwater habitats as juveniles and grow quickly in marine habitats. Putative spawning populations are rare in the North American Arctic and limited to pink salmon in drainages north of Point Hope, Alaska, chum salmon spawning rivers draining to the northwestern Beaufort Sea, and small populations of chum and pink salmon in Canada’s Mackenzie River. Pacific salmon have colonized several large river basins draining to the Kara, Laptev and East Siberian seas in the Russian Arctic. These populations probably developed from hatchery supplementation efforts in the 1960’s. Hundreds of populations of Arctic Atlantic salmon (Salmo salar) are found in Russia, Norway and Finland. Atlantic salmon have extended their range eastward as far as the Kara Sea in central Russian. A small native population of Atlantic salmon is found in Canada’s Ungava Bay. The northern tip of Quebec seems to be an Atlantic salmon migration barrier for other North American stocks. Compatibility between life history requirements and ecological conditions are prerequisite for salmon colonizing Arctic habitats. Broad-scale predictive models of climate change in the Arctic give little information about feedback processes contributing to local conditions, especially in freshwater systems. This paper reviews the recent history of salmon in the Arctic and explores various patterns of climate change that may influence range expansions and future sustainability of salmon in Arctic habitats. A summary of the research needs that will allow informed expectation of further Arctic colonization by salmon is given.     

Melanin concentrating hormone (MCH) effects on teleost (Chrysiptera cyanea) melanophores

The in vitro biological actions of synthetic chum salmon melanin concentrating hormone (MCH) on melanophores of the blue damselfish (a teleost), Chrysiptera cyanea, were studied. This cyclic heptadecapeptide stimulated melanosome (melanin granule) aggregation (centripetal migration) within melanophores at a threshold concentration of about 10(-10) M. The action of this putative hormone was not blocked by alpha- or beta-adrenoceptor antagonists. It was concluded that the effects of MCH were direct and were not mediated indirectly through the actions of adrenergic neurotransmitters released from nerve terminals. Further evidence for this view comes from the observation that, unlike the case of neurotransmitter release, melanosome aggregation in response to MCH proceeded in the absence of calcium. The possible role of MCH in the control of color change of teleost fishes is discussed.