Detection of Renibacterium salmoninarum antigen in migrating adult chum salmon (Oncorhynchus keta) in Japan.

Renibacterium salmoninarum antigen was detected in the kidney of migrating chum salmon (Oncorhynchus keta) using the indirect dot blot assay and indirect fluorescent antibody test. The adult chum salmon had migrated into a bay in which cultured coho salmon infected with R. salmoninarum were present. Antigen was detected in 5% of the chum salmon although they did not have clinical signs of bacterial kidney disease (BKD). This report describes the first case of R. salmoninarum antigen detection among wild chum salmon populations in eastern Asia.     

Shedding of Renibacterium salmoninarum by infected chinook salmon Oncorhynchus tschawytscha

Laboratory studies of the transmission and pathogenesis of Renibacterium salmoninarum may describe more accurately what is occurring in the natural environment if test fish are infected by waterborne R. salmoninarum shed from infected fish. To quantify bacterial shedding by chinook salmon Oncorhynchus tschawytscha at 13 degrees C in freshwater, groups of fish were injected intraperitoneally with R. salmoninarum at either 1.3 x 10(6) colony forming units (CFU) fish (-1) (high-dose injection group) or 1.5 x 10(3) CFU fish (-1) (low-dose injection group). R. salmoninarum infection levels were measured in the exposed fish by the enzyme-linked immunosorbent assay (BKD-ELISA). At regular intervals for 30 d, the numbers of R. salmoninarum shed by the injected fish were calculated on the basis of testing water samples by the membrane filtration-fluorescent antibody test (MF-FAT) and bacteriological culture. Mean BKD-ELISA optical densities (ODs) for fish in the low-dose injection group were not different from those control fish (p > 0.05), and no R. salmoninarum were detected in water samples taken up to 30 d after injection of fish in the low-dose group. By 12 d after injection a proportion of the fish from the high-dose infection group had high (BKD-ELISA OD > or = 1.000) to severe (BKD-ELISA OD > or = 2.000) R. salmoninarum infection levels, and bacteria were detected in the water by both tests. However, measurable levels of R. salmoninarum were not consistently detected in the water until a proportion of the fish maintained high to severe infection levels for an additional 8 d. The concentrations of R. salmoninarum in the water samples ranged from undetectable up to 994 cells ml(-1) on the basis of the MF-FAT, and up to 1850 CFU ml(-1) on the basis of bacteriological culture. The results suggest that chinook salmon infected with R. salmoninarum by injection of approximately 1 x 10(6) CFU fish (-1) can be used as the source of infection in cohabitation challenges beginning 20 d after injection.     

Metabolic pathways of carotenoids in chum salmon Oncorhynchus keta during spawning migration

1. Based on the contents and individual composition of carotenoids in the muscle, serum and ovaries of chum salmon during spawning migration, the reductive metabolism of astaxanthin to zeaxanthin was presumed to take place in the muscle of both male and female. 2. The metabolic rates of zeaxanthin and 4-keto-zeaxanthin in female serum were much faster than those in male serum.     

Persistence of egg pocket architecture in redds of chum salmon, Oncorhynchus keta

Synopsis Analysis of frozen cores of gravel surrounding the egg pockets of chum salmon, Oncorhynchus keta, collected in the fall revealed that spawning activity by females purged about 75 % of the fine sediments from the stream bed. The egg pocket was one of four distinct vertical strata detected in the cores. There was an undisturbed layer below the egg pocket, and separate bridge and cover strata above the egg pocket, all defined by different particle size distributions. However, by spring most of the egg pockets had been infiltrated with fine sediment and the particle size distribution approached background levels. The most likely physical factors responsible for these results were: (1) intrusion of fine sediments through the cleaned surface gravel, (2) lateral subsurface migration of fine sediment into interstitial voids, (3) scour of the surface gravel and subsequent deposition of a sand rich bedload, and (4) superimposed spawning activity of other fish, causing disturbance of the cleaned surface gravel and exposing the egg pocket to intrusion of fine particles. We conclude that, while female salmon substantially affect the physical environment of their embryos, subsequent sediment transport processes and fine bedload flux tend to return this environment to pre-spawning conditions.     

Identification of the sex chromosome pair in chum salmon (Oncorhynchus keta) and pink salmon (Oncorhynchus gorbuscha)

Fluorescence in situ hybridization (FISH) using a probe to the male-specific GH-Y (growth hormone pseudogene) was used to identify the Y chromosome in the karyotypes of chum salmon (Oncorhynchus keta) and pink salmon (Oncorhynchus gorbuscha). The sex chromosome pair is a small acrocentric chromosome pair in chum salmon and the smallest metacentric chromosome pair in pink salmon. Both of these chromosome pairs are morphologically different from the sex chromosome pairs in chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch). The 5S rRNA genes are on multiple chromosome pairs including the sex chromosome pair in chum salmon, but at the centromeres of two autosomal metacentric pairs in pink salmon. The sex chromosome pairs and the chromosomal locations of the 5S rDNA appear to be different in all five of the North American Pacific salmon species and rainbow trout. The implications of these results for evolution of sex chromosomes in salmonids are discussed.     

Absence of a gamma-melanocyte-stimulating hormone sequence in proopiomelanocortin mRNA of chum salmon Oncorhynchus keta

1. Complete nucleotide sequence of one of the salmon proopiomelanocortin mRNAs (POMC mRNAs) was determined. 2. The region corresponding to gamma-melanocyte-stimulating hormone (gamma-MSH) was lacking in salmon POMC mRNA, although overall organization of the multi-hormone structure was exactly the same as that of mammalian POMC mRNAs. 3. The possible evolutional history of POMC mRNA in mammalian species may be revealed from the finding of this characteristic that salmon POMC mRNA lacks the region corresponding to gamma-MSH.     

Microsatellite variability and differentiation of hatchery stocks of chum salmon Oncorhynchus keta Walbaum in Sakhalin

Variability at eight microsatellite loci was examined in five populations of chum salmon Oncorhynchus keta Walbaum from Sakhalin hatcheries. The population of Kalinino hatchery had the lowest heterozygosity and the lowest average number of alleles per locus. The populations examined exhibited significant differentiation, θ_ST = 0.026 on average per locus. The maximum genetic differences were found between the populations of the Kalinino and the Ado-Tymovo hatcheries; the latter differs from the remaining populations also by the highest number and high frequencies of specific alleles. The genetic features of the Taranai hatchery population, observed at microsatellite loci, reflect its “mixed” origin.     

Isolation of apolipoproteins from carotenoid-carrying lipoprotein in the serum of chum salmon, Oncorhynchus keta

Carotenoid-carrying lipoprotein (CCL) was rapidly isolated from the high density lipoprotein (HDL) fraction of the upstream migrating male chum salmon (Oncorhynchus keta) by a single-step density gradient ultracentrifugation. The two apolipoproteins (Mr = 24,000 and 12,000; designated apo-I and apo-II, respectively) were readily dissociated and separated in 0.1% SDS by gel filtration chromatography. Prominent features of the amino acid composition in the CCL included the relative high levels of glutamic acid, alanine, leucine, and lysine, and the low cysteine content. Apo-I, as well as the CCL, was rich in glutamic acid, alanine, leucine, and lysine. Compared to the amino acid composition of apo-I, apo-II included relatively high levels of glycine and tyrosine, and low threonine, serine, and arginine contents. When the intact CCL particle was treated with trypsin, apo-I was rapidly proteolyzed, while apo-II was resistant. However, both apo-I and apo-II isolated from the CCL particle were readily digested with trypsin. This suggested that a different structural arrangement rather than the amino acid compositions of the apolipoproteins was associated with the limited trypsin digestion of the CCL particle. Apo-II may be sheltered from the aqueous environment and lie partly within the CCL particle. The properties of both the HDL fraction and apolipoproteins from pink salmon (Oncorhynchus gorbuscha) were similar to those of the CCL from chum salmon.     

Microsatellite variability and differentiation of hatchery stocks of chum salmon Oncorhynchus keta Walbaum in Sakhalin

Variability at eight microsatellite loci was examined in five populations of chum salmon Oncorhynchus keta Walbaum from Sakhalin hatcheries. The population of Kalinino hatchery had the lowest heterozygosity and the lowest average number of alleles per locus. The populations examined exhibited significant differentiation, theta ST = 0.026 on average per locus. The maximum genetic differences were found between the populations of the Kalinino and the Ado-Tymovo hatcheries; the latter differs from the remaining populations also by the highest number and high frequencies of specific alleles. The genetic features of the Taranai hatchery population, observed at microsatellite loci, reflect its "mixed" origin.     

Energy expenditures during spawning by chum salmon Oncorhynchus keta (Walbaum) in British Columbia

Physiological telemetry and proximate tissue analyses were used to assess energy expended by chum salmon Oncorhynchus keta on various behaviours during spawning in Kanaka Creek, British Columbia, Canada, and results were compared with published data on Fraser River sockeye salmon Oncorhynchus nerka , the only other species for which both types of measurements have been taken. Chum salmon arrived at the spawning grounds with body energy densities of 4·84 MJ kg⁻¹ in males and 4·62 MJ kg⁻¹ in females, lower than most sockeye salmon populations, and died with energy densities of c . 4 MJ kg⁻¹, similar to that observed in sockeye salmon and other salmonids. Moisture levels generally increased in body tissues over the spawning life, particularly in female gonads, and lipid levels decreased. Declines in protein observed over the spawning life of other Pacific salmon Oncorhynchus sp. were less evident in Kanaka Creek chum salmon. Holding behaviour constituted the dominant component of the activity schedule and energy budget of both sexes. After holding, the most expensive behaviours were nest digging in females and aggressive displays in males. Dominant males expended the most energy on behaviours each day, as indexed by oxygen consumption (3600 mgO₂ kg⁻¹), while satellite males expended nearly as much (3504 mgO₂ kg⁻¹) but females expended considerably less (2327 mgO₂ kg⁻¹). Kanaka chum salmon engaged more frequently in energetically expensive reproductive behaviours than Stuart River sockeye salmon.     

Hybrids between chum Oncorhynchus keta and pink Oncorhynchus gorbuscha salmon: age,growth and morphology and effects on salmon production

Mature hybrids between chum salmon Oncorhynchus keta and pink salmon Oncorhynchus gorbuscha, which were identified by an intermediate colour pattern, were caught at the Kurilsky Hatchery, Iturup Island, Russia. Most of them were female and 3 years old (a partial freshwater year and 2 marine years), which is intermediate between the ages of maturity of the parental species. The hybrids exceed both parental species in the rate of growth, are large in size and robust and might successfully compete for mating in the wild or be chosen for artificial reproduction. The ratio of the scale length over width, R, is oblate (R < 1), whereas scales of the parental species are prolate (R > 1). From scale analyses, the c.v. in body size of hybrid females at the second marine year is twice that of O. keta, which suggests developmental instability in the hybrid. A dynamic model predicted that continuing hybridization at a low rate does not produce a substantial hybrid load due to selection against advanced‐generation hybrids and backcrosses. A high hybridization rate, however, may be an additional risk for genetic management and should be taken into account in programmes of artificial reproduction of Pacific salmon Oncorhynchus spp., although such hybrids might have commercial use in confined production systems.     

Embryonic origin and development of the corpuscles of Stannius in chum salmon (Oncorhynchus keta)

Summary An immunocytochemical technique was used to follow the embryological origin and development of the corpuscles of Stannius (CS) in the chum salmon, Oncorhynchus keta. Stanniocalcin immunoreactive (ir-) cells can be observed as early as 13 days before hatching. The ir-CS cells appear in clusters of variable size in close association with nephric ducts. In addition, individual ir-cells also occur at this stage amoung epithelial cells of the nephric ducts. these individual cells may give rise to clusters which subsequently increase in size, the largest reaching 100 m in diameter by the time of hatching. During this period, dispersed CS cells become evident and develop into secondary clusters in the vicinity of the primary clusters. These clusters appear to fuse to form larger clusters with a lobular structure. Transfer of the larvae (20 days after hatching) from fresh water to 50% seawater, accelerates the development of the CS tissue, suggesting an important role of the CS in seawater adaptation.     

Spawning tactics of summer chum salmon Oncorhynchus keta in relation to channel complexity and hyporheic exchange

Vertical hydraulic gradient, channel hydraulic, and substratum data were collected at active chum salmon redds to evaluate their influence on redd site selection in the Kwethluk River, a wandering gravel-bedded tributary of Alaska’s Lower Kuskokwim River. Two distinct summer chum salmon spawning tacitcs: primary- and off-channel groups spawning in different hydraulic and thermal environments. Channel hydraulics, ground-surface water exchanges, and bed sediment data were collected throughout the range of topographic conditions at sites occupied and unoccupied by spawners. Analyses of these data showed that redd site selection was incoherent with channel hydraulics and substratum size, when all channel types were considered. Rather, spawning was associated with the exchange of river and groundwater at four spatial scales. In primary channels, chum salmon spawned only in reaches where the regional hydraulic gradient (regional scale) promoted the penetration of river water, or downwelling, into the bed sediments. Within these reaches, primary-channel spawning was influenced by bed topography (fluvial scale) that promoted strong localized downwelling; a logit model, fitted to constituent hydraulics, discriminated between selected and unselected sites with 89 % accuracy. In contrast, spawners in off-channel habitats (flood and spring channels) selected areas of upwelling groundwater, regardless of channel hydraulics and the regional hydraulic gradient. In parafluvial flood channels, spawners selected localized upwelling associated with short groundwater flow paths (parafluvial scale). In spring channels, within the floodplain’s forested riparia (orthofluvial scale), spawners eschewed areas of localized downwelling and uniformly selected upwelling zones feeding these channels. Thus, redd selectivity differentiated two spawning tactics (groups) in this complex channel network where ground and surface water exchange is an important predictor of spawning habitat.     

Relation between size-at-maturity and survival of progeny in chum salmon, Oncorhynchus keta (Walbaum)

Data on age- and size-at-maturity, growth, and abundance of chum salmon were collected from 1959 to 1977 at Olsen Creek in Prince William Sound, Alaska. Age composition of spawners (3 to 6-year-olds) varied from year to year: 4-year-old fish were the dominant age group in most (16 out of 19) years and 6-year-old fish usually represented less than 1 % of the returns. Mean size of older spawners was significantly larger than that of younger spawners. Size-at-maturity was similar among fish from different broods maturing at different ages in the same year. Size-at-maturity and survival of progeny were significantly related. The larger the mean size of spawners, the higher the survival rate to adulthood of their progeny. Possible reasons for this relationship are discussed.     

Genetic differentiation among chum salmon, Oncorhynchus keta (Walbaum), from Primorye and Sakhalin

Mitochondrial DNA (mtDNA) was examined in six wild populations of chum salmon ( Oncorhynchus keta Walbaum) distributed over the Primorye Region which extends approximately 1000 km along the Sea of Japan coast, and six populations from Sakhalin, using restriction enzyme analysis. By means of two restriction enzymes ( Bam HI and Eco 81I) eight mtDNA clonal lines were revealed in the 346 chum salmon studied. Mitochondrial DNA variants grouped the fish into two major clusters representing the Primorye and Sakhalin regions. Analysis of different chum salmon generations showed stability in the temporal population genetic structure in the three Primorye populations studied, but instability in the Sakhalin population of the Naiba River. We succeeded in detecting four major mtDNA clonal variants in Primorye chum salmon. The geographic distribution of clonal frequencies in Primorye populations has a clinal U-shape associated with the north-south axis of the Primorye region. On the whole, Sakhalin populations are less heterogeneous than Primorye ones. Two hatchery-seeded stocks from south west Sakhalin showed no mtDNA clonal variation.     

Prevalence and analysis of Renibacterium salmoninarum infection among juvenile Chinook salmon Oncorhynchus tshawytscha in North Puget Sound

Renibacterium salmoninarum causes bacterial kidney disease (BKD), a chronic and sometimes fatal disease of salmon and trout that could lower fitness in populations with high prevalences of infection. Prevalence of R. salmoninarum infection among juvenile Chinook salmon Oncorhynchus tshawytscha inhabiting neritic marine habitats in North Puget Sound, Washington, USA, was assessed in 2002 and 2003. Fish were collected by monthly surface trawl at 32 sites within 4 bays, and kidney infections were detected by a quantitative fluorescent antibody technique (qFAT). The sensitivity of the qFAT was within an order of magnitude of the quantitative real-time PCR (qPCR) sensitivity. Prevalence of infection was classified by fish origin (marked/hatchery vs. unmarked/likely natural spawn), month of capture, capture location and stock origin. The highest percentages of infected fish (63.5 to 63.8%) and the greatest infection severity were observed for fish collected in Bellingham Bay. The lowest percentages were found in Skagit Bay (11.4 to 13.5%); however, there was no difference in prevalence between marked and unmarked fish among the capture locations. The optimal logistic regression model of infection probabilities identified the capture location of Bellingham Bay as the strongest effect, and analysis of coded wire tagged (CWT) fish revealed that prevalence of infection was associated with the capture location and not with the originating stock. These results suggest that infections can occur during the early marine life stages of Chinook salmon that may be due to common reservoirs of infection or horizontal transmission among fish stocks.     

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.