Lacustrine Sockeye Salmon Research Articles

Incorporating ecological heterogeneity and intraspecific variation differentiates complex interactions between apex predators and stocked fish

Ecological heterogeneity and intraspecific variation can impact energy flow from the base of the food web to top predators. We evaluated the effect of intraspecific variation on estimates of lake trout ( Salvelinus namaycush) consumption of stocked kokanee (lacustrine sockeye salmon, Oncorhynchus nerka) in a 390 ha oligotrophic lake with two distinct basins. Lake trout stomach content analyses, stable isotope niche space, and catch rates indicated high intraspecific variation in resource use across habitats and basins. Intraspecific variation and ecological heterogeneity were incorporated into two bioenergetics modeling approaches: one lake-wide model, and one partitioned model that accounted for differences in lake trout diet composition and population size across habitats. The ecologically partitioned model highlighted that lake trout consumption was primarily in the epilimnion of one basin, while the lake-wide, unpartitioned model performed similarly but failed to provide ecological context for where that consumption occurred. Incorporating ecological heterogeneity and intraspecific variation into bioenergetic models can more accurately represent top predators foraging patterns across habitats and inform management actions to mitigate impacts to stocked fish.

Density Dependence in Three Snake River Sockeye Salmon Nursery Lakes in Central Idaho

AbstractSnake River Sockeye Salmon Oncorhynchus nerka, listed as an endangered species in 1991, currently inhabit three nursery lakes (Redfish, Pettit, and Alturas lakes) in the Sawtooth Valley, Idaho. Conspecific kokanee (lacustrine Sockeye Salmon) are also present in the lakes. Snake River Sockeye Salmon recovery efforts, initially focused on genetic conservation, are now attempting to rebuild naturally spawning populations using hatchery supplementation. However, in Sockeye Salmon nursery lakes, density dependence is frequently observed when elevated O. nerka abundance leads to declines in zooplankton biomass, body size, and shifts in community composition. In turn, these changes lead to reductions in juvenile O. nerka growth rates, survival, and adult returns. We examined a long‐term data set of O. nerka population metrics and associated zooplankton community metrics. We found evidence of density dependence within and among nursery lakes. We detected differences in zooplankton biomass, lengths of preferred zooplankton prey (Daphnia spp. and cyclopoid copepods), parr growth rates, and age‐1 smolt size among the three lakes. We found negative relationships between O. nerka density and zooplankton biomass and size. We identified positive relationships between zooplankton biomass and two response variables: smolt size at migration and growth rates of hatchery parr. The relationships were generally similar among lakes. Variable outcomes were a result of differences in O. nerka density (or zooplankton biomass), controlled primarily by the relative proportion of spawning and rearing habitat in each lake. Understanding unique lake habitats, ecological interactions, and the role of density dependence is germane to management of Snake River Sockeye Salmon populations.

Olfactory behavioural and neural responses of planktivorous lacustrine sockeye salmon (Oncorhynchus nerka) to prey odours.

Fish use a variety of sensory systems when foraging. Salmonids are generally considered visual feeders. However, some species feed on zooplanktons under dark conditions, suggesting they also detect prey using nonvisual cues. Under experimental conditions, hatchery-reared rainbow trout (Oncorhynchus mykiss) have been shown to use olfaction when searching for food pellets, but olfactory foraging has not been documented in wild salmonids. In the present study, to examine their behavioural response and neural activity in the olfactory nervous system using c-fos expression as a neural molecular marker, immature wild-caught lacustrine sockeye salmon (Oncorhynchus nerka) in a flow-through aquarium were exposed to zooplanktons (Daphnia spp.) extract including zooplanktons odorant and to dimethyl sulfide. The salmon exposed to zooplanktons odour increased their total swimming distance and time, numbers of turns and ascents, and c-fos expression in the olfactory bulb, suggesting that they can detect zooplanktons extract to locate prey in the laboratory experiments. However, no response was seen in those exposed to dimethyl sulfide. The results of this study suggest that prey odour may serve as a chemosensory cue for wild immature salmonids.

Age‐Structured Interactions among Reintroduced Sockeye Salmon, Resident Kokanee, Invasive Mysids, and their Zooplankton Prey in Skaha Lake, British Columbia

AbstractIn 2004, after an 85+ year absence, Sockeye Salmon Oncorhynchus nerka were reintroduced into Skaha Lake, British Columbia. Prior to this, the lake’s planktivore community was dominated by kokanee (lacustrine Sockeye Salmon) and an invasive freshwater shrimp Mysis diluviana, and British Columbia fisheries managers were concerned that reintroduced Sockeye Salmon fry might reduce the abundance of zooplankton prey and negatively affect the abundance and size of kokanee available for the recreational fishery. We looked for possible adverse effects by introducing contrasting densities (0–2,309 fish/ha) of marked, hatchery‐origin Sockeye Salmon fry to Skaha Lake over 12 years (2005–2017). During each year, we monitored state change indicators of lake flushing, water temperature, nutrients, phytoplankton, microzooplankton, M. diluviana, kokanee, and Sockeye Salmon. Zooplankton consumption by Sockeye Salmon, kokanee, and M. diluviana was estimated via bioenergetics models. We found that (1) average densities of pelagic fish gradually increased above premanipulation densities and (2) survival (egg to winter) of kokanee fry was variable but positively associated with increased abundances of Sockeye Salmon fry. Average survival of age‐0 to age‐3+ kokanee in Skaha Lake exhibited no significant trends. We also found that (3) growth rates for age‐0 Sockeye Salmon fry and kokanee were stable during 2005–2013, despite moderate increases in fish abundance, but declined in 2017. This decline was associated with record‐high biomasses of kokanee and M. diluviana, record rates of zooplankton loss from predation and lake flushing, and reduced zooplankton production. We found that (4) bioenergetics data showed that, on average, 1.8% of annual zooplankton prey consumption was attributable to hatchery‐origin Sockeye Salmon fry, 2.8% to Lake Whitefish Coregonus clupeaformis, 13.9% to older kokanee, and 79.6% of the zooplankton was consumed by M. diluviana. We concluded that during 2005–2015 consumption by planktivores never exceeded production by zooplankton, but in 2017, when lake flushing rates were exceptionally high, consumption by planktivores exceeded lake‐carrying capacity for pelagic fish. Sockeye Salmon fry played virtually no part in these events.

Size‐Dependent Retention of Pelagic‐Oriented Kokanee in Multimesh Gill Nets

AbstractRecent studies evaluating the size selectivity of standard, horizontal, benthic gill nets for some common sport fish have demonstrated congruence across regions and gear configurations. Studies evaluating retention in gill nets designed to sample pelagic‐oriented fish (e.g., vertical and curtain nets) are rare, which has limited corresponding assessments of generality. This study estimated the retention of kokanee Oncorhynchus nerka (lacustrine Sockeye Salmon) in multimesh vertical gill nets using catch data compiled over three decades from a large montane reservoir in Colorado. The corresponding best‐fit retention model was compared with that developed for kokanee in Idaho using multimesh curtain nets. There was strong congruence (Pearson's r = 0.98) between the total retention values (integrated over all mesh sizes) estimated by the two models for kokanee 50–430 mm total length, and the values followed a 1:1 relationship. This result indicated that the retention of fish in pelagic gill nets may also be largely conserved across regions and gear configurations. Thus, the retention models for kokanee compared in this study should be flexible and broadly applicable. These properties enable practitioners to easily adjust length‐frequency distributions for bias arising from size‐dependent retention when minimally biased estimates of size structure are needed for addressing management or research questions.

Recovery of Sockeye Salmon in the Elwha River, Washington, after Dam Removal: Dependence of Smolt Production on the Resumption of Anadromy by Landlocked Kokanee

AbstractPacific salmon Oncorhynchus spp. are adept at colonizing habitat that has been reopened to anadromous passage. Sockeye Salmon O. nerka are unique in that most populations require lakes to fulfill their life history. Thus, for Sockeye Salmon to colonize a system, projects like dam removals must provide access to lakes. However, if the lakes contain landlocked kokanee (lacustrine Sockeye Salmon), the recovery of Sockeye Salmon could be mediated by interactions between the two life history forms and the processes associated with the resumption of anadromy. Our objective was to evaluate the extent to which estimates of Sockeye Salmon smolt production and recovery are sensitive to the resumption of anadromy by kokanee after dam removal. We informed the analysis based on the abiotic and biotic features of Lake Sutherland, which was recently opened to passage after dam removal on the Elwha River, Washington. We first developed maximum expectations for the smolt‐producing capacity of Lake Sutherland by using two predictive models developed from Sockeye Salmon populations in Alaska and British Columbia: one model was based on the mean seasonal biomass of macrozooplankton, and the other was based on the euphotic zone volume of the lake. We then constructed a bioenergetics‐based simulation model to evaluate how the capacity of Lake Sutherland to rear yearling smolts could change with varying degrees of anadromy among O. nerka fry. We demonstrated that (1) the smolt‐producing capacity of a nursery lake for juvenile Sockeye Salmon changes in nonlinear ways with changes in smolt growth, mortality, and the extent to which kokanee resume anadromy after dam removal; (2) kokanee populations may be robust to changes in abundance after dam removal, particularly if lakes are located higher in the watershed on tributaries separate from where dams were removed; and (3) the productivity of newly establishing Sockeye Salmon can vary considerably depending on whether the population becomes rearing limited or is recruitment limited and depending on how adult escapement is managed.Received March 9, 2016; accepted August 6, 2016 Published online October 11, 2016

Influence of Habitat Characteristics on Shore‐Spawning Kokanee

AbstractSockeye Salmon Oncorhynchus nerka and kokanee (lacustrine Sockeye Salmon) commonly spawn in both lentic and lotic environments; however, the habitat requirements of shore spawners are virtually unknown relative to those of stream spawners. A laboratory experiment and an in situ incubation study were conducted to better understand the influence of habitat characteristics on the shoreline incubation success of kokanee. The laboratory experiment assessed kokanee intragravel survival, fry emergence, and fry condition in response to eight substrate treatments. The in situ study, conducted at three major shoreline spawning sites in Lake Pend Oreille, Idaho, evaluated the effect of depth, substrate composition, dissolved oxygen, shoreline slope, and groundwater on intragravel survival. Substrate size composition was generally a poor predictor of survival in both the laboratory experiment and in situ study; although, fry condition and counts of emerged fry in the laboratory were lowest for the substrate treatment that had the highest proportion of fine sediment. Results of the in situ study suggest that groundwater flow plays an important role in enhancing intragravel survival in habitats generally considered unsuitable for spawning.Received January 7, 2014; accepted May 28, 2014

The genetic population structure of lacustrine sockeye salmon, Oncorhynchus nerka, in Japan as the endangered species

Lacustrine sockeye salmon (Oncorhynchus nerka) are listed as an endangered species in Japan despite little genetic information on their population structure. In order to clarify the genetic diversity and structure of Japanese populations for evaluating on the bottleneck effect and an endangered species, we analyzed the ND5 region of mitochondrial DNA (mtDNA) and 45 single nucleotide polymorphisms (SNPs) in 640 lacustrine sockeye salmon in Japan and 80 anadromous sockeye salmon in Iliamna Lake of Alaska. The genetic diversity of the Japanese population in both mtDNA and SNPs was significantly less than that of the Iliamna Lake population. Moreover, all Japanese populations had SNP loci deviating from the HWE. In spite of low genetic diversity, the SNP analyses resulted that the Japanese population was significantly divided into three groups. These suggest that Japanese sockeye salmon populations should be protected as an endangered species and genetically disturbed by the hatchery program and transplantations.

Relative Genetic Diversity Estimates among Four Pacific Salmonids

AbstractThe genetic diversity within a species is a reflection of its evolutionary past and ongoing mutation, drift, and adaptation. Species that occupy a diverse range of habitats and that have adapted for generations under selective pressures will carry a genetic imprint of that adaptation within specific functional genes. Alternatively, genetic diversity may be reduced owing to historical bottlenecks and genetic drift. In this study, genetic diversity was estimated in four species of Pacific salmon (rainbow trout, steelhead [anadromous rainbow trout] Oncorhynchus mykiss, Chinook salmon O. tshawytscha, coho salmon O. kisutch, and sockeye salmon, kokanee [lacustrine sockeye salmon] O. nerka) using 563–608 kilo–base pairs of DNA sequence data from 32 individuals per species. Individual samples were chosen to represent the major lineages of each species across their natural ranges. The results show the highest genetic diversity estimates for rainbow trout and the lowest for sockeye salmon. Statistically significant differences were observed between the species with the highest genetic diversity (rainbow trout) and the three remaining species. Loci with the highest genetic diversity within each species are listed as potentially being influenced by balancing selection.

Olfactory responses to natal stream water in sockeye salmon by BOLD fMRI.

Many studies have shown that juvenile salmon imprint olfactory memory of natal stream odors during downstream migration, and adults recall this stream-specific odor information to discriminate their natal stream during upstream migration for spawning. The odor information processing of the natal stream in the salmon brain, however, has not been clarified. We applied blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging to investigate the odor information processing of the natal stream in the olfactory bulb and telencephalon of lacustrine sockeye salmon (Oncorhynchus nerka). The strong responses to the natal stream water were mainly observed in the lateral area of dorsal telencephalon (Dl), which are homologous to the medial pallium (hippocampus) in terrestrial vertebrates. Although the concentration of L-serine (1 mM) in the control water was 20,000-times higher than that of total amino acid in the natal stream water (47.5 nM), the BOLD signals resulting from the natal stream water were stronger than those by L-serine in the Dl. We concluded that sockeye salmon could process the odor information of the natal stream by integrating information in the Dl area of the telencephalon.

Olfactory imprinting of amino acids in lacustrine sockeye salmon.

Juvenile salmon have an olfactory ability to imprint their natal stream odors, but neither the odor properties of natal stream water nor the imprinting timing and duration have been clarified as yet. Here we show, using electrophysiological and behavioral experiments, that one-year-old lacustrine sockeye salmon (Oncorhynchus nerka) can be imprinted around the stage of parr-smolt transformation (PST) by a single amino acid, 1 µM L-proline (Pro), or L-glutamic acid (Glu). We also show by real-time PCR that changes occur in mRNA levels of the salmon olfactory imprinting-related gene (SOIG) around PST. The electro-olfactogram (EOG) responses of test fish exposed to Pro in March (before PST) and April–June (during PST) for 2 weeks were significantly (1.7-fold) greater than those of non-exposed control fish, but not those of test fish exposed in July (after PST). When Pro and control water were added to the water inlets of a two-choice test tank during the spawning season 2 years after the test water exposure, 80% of maturing and matured test fish exposed before and during PST showed a preference for Pro, whereas those exposed after PST did not. The EOG response of test fish exposed to Pro or Glu for 1 hour, 6 hours, 1 day, 7 days, or 14 days in May revealed that only the response after 14 days of exposure was significantly (1.8-fold) greater than the control. The expression levels of SOIG mRNA increased before and during PST, and decreased after PST. We conclude that one-year-old lacustrine sockeye salmon can be imprinted by a single amino acid before and during PST, and that imprinting requires exposure for at least 14 days.

Evaluating the Reintroduction Potential of Lahontan Cutthroat Trout in Fallen Leaf Lake, California

AbstractWe evaluated the potential for reintroducing Lahontan cutthroat trout Oncorhynchus clarkii henshawi, a species listed under the Endangered Species Act, into a lacustrine system where the biotic community has changed dramatically since the species' extirpation there. Since 2002, 76,547 Lahontan cutthroat trout have been reintroduced into Fallen Leaf Lake, California; we used creel surveys, diet data, mark–recapture methods, bioenergetics modeling, and netting data across seasons to evaluate the habitat use, growth, and relative abundance of Lahontan cutthroat trout and the abundance, diet, habitat use, and predation by nonnative species. Sampling totals (n = 2) and survey observations (n = 3) indicate low survival and abundance of reintroduced fish and together with creel data indicate the importance of epilimnetic habitats across size‐classes. Despite substantial growth, Lahontan cutthroat trout exhibited low condition factor values (average = 0.69). We found substantial predation pressure from a large population of lake trout Salvelinus namaycush (Ṋ = 8,799 fish; 95% confidence interval [CI] = 4,990–16,530 fish); analysis of lake trout diets showed an increase in piscivory and in the percentage of stomachs containing Lahontan cutthroat trout anchor tags with increasing predator size. Overall, we estimated that lake trout consumed over 38% of reintroduced Lahontan cutthroat trout (mean number consumed = 7,736 fish; 95% CI = 4,388–14,534 fish). With bioenergetics modeling, however, we estimated that lake trout consumed considerable amounts of salmonid biomass during this period (mean biomass = 3,137 kg; 95% CI = 1,779–5,893 kg), which greatly exceeded the biomass of Lahontan cutthroat trout reintroduced in 2006. During the stratification period, there was little overlap in habitat use between lake trout and Lahontan cutthroat trout, but overlap was high during the spring and autumn. We found moderate‐sized populations of nonnative brown trout Salmo trutta, kokanee O. nerka (lacustrine sockeye salmon), and rainbow trout O. mykiss. Together, our results suggest that Lahontan cutthroat trout have few refugia from direct and indirect negative interactions with nonnative species and that alternative approaches are needed.

Molecular characterization and histochemical demonstration of salmon olfactory marker protein in the olfactory epithelium of lacustrine sockeye salmon ( Oncorhynchus nerka)

Despite the importance of olfactory receptor neurons (ORNs) for homing migration, the expression of olfactory marker protein (OMP) is not well understood in ORNs of Pacific salmon (genus Oncorhynchus). In this study, salmon OMP was characterized in the olfactory epithelia of lacustrine sockeye salmon ( O. nerka) by molecular biological and histochemical techniques. Two cDNAs encoding salmon OMP were isolated and sequenced. These cDNAs both contained a coding region encoding 173 amino acid residues, and the molecular mass of the two proteins was calculated to be 19,581.17 and 19,387.11 Da, respectively. Both amino acid sequences showed marked homology (90%). The protein and nucleotide sequencing demonstrates the existence of high-level homology between salmon OMPs and those of other teleosts. By in situ hybridization using a digoxigenin-labeled salmon OMP cRNA probe, signals for salmon OMP mRNA were observed preferentially in the perinuclear regions of the ORNs. By immunohistochemistry using a specific antibody to salmon OMP, OMP-immunoreactivities were noted in the cytosol of those neurons. The present study is the first to describe cDNA cloning of OMP in salmon olfactory epithelium, and indicate that OMP is a useful molecular marker for the detection of the ORNs in Pacific salmon.

Identification of an olfactory imprinting-related gene in the lacustrine sockeye salmon, Oncorhynchus nerka

The olfactory system of salmonids is essential for imprinting and the subsequent homing migration. Olfactory imprinting-related genes were identified in the olfactory system of 1- and 3-year-old lacustrine sockeye salmon (Oncorhynchus nerka) using a subtractive hybridization technique of representational difference analysis (cDNA-RDA). We have obtained a partial clone from a subtractive cDNA library of 1-year-old fish that contains a 756 bp open reading frame coding for a putative protein with 252 amino acid residues named the Sockeye salmon Olfactory system Imprinting related Gene (SOIG). By northern hybridization, the SOIG mRNA was only expressed in the olfactory epithelium and not in other tissues. In situ hybridization showed that the expression of SOIG mRNA was observed in the olfactory receptor cells and basal cells of the olfactory epithelium. This suggests that SOIG could have specific and important roles in olfactory system.

Cloning and characterization of an odorant receptor in five Pacific salmon

The olfactory system of fish is extremely important as it is able to recognize and distinguish a vast of odorous molecules involved in wide ranges of behaviors including reproduction, homing, kin recognition, feeding and predator avoidance; all of which are paramount for their survival. We cloned and characterized one type olfactory receptors (ORs) from five congeneric salmonids: lacustrine sockeye salmon ( Oncorhynchus nerka), pink salmon ( O. gorbuscha), chum salmon ( O. keta), masu salmon ( O. masou) and rainbow trout ( O. mykiss). Lacustrine sockeye salmon olfactory receptor 1 (LSSOR1) showed high sequence homology to the OR subfamily, and was expressed only in the olfactory epithelium (as indicated by PCR amplified genomic DNA and cDNA). OR genes from the five salmonids examined all showed strong homology (96–99%) to each other. Hypervariable regions, believed to be ligand-binding pockets, showed homologous completely matched amino acid sequences except for one amino acid in pink salmon olfactory receptor 1 (PSOR1), revealing that these ORs may be well conserved among salmon species. These results suggest that the isolated 5 salmonid ORs might play an important role in salmon life cycles.

Long‐Term Population Dynamics of the Endangered Snake River Sockeye Salmon: Evidence of Past Influences on Stock Decline and Impediments to Recovery

AbstractDeclines in populations of Pacific salmon Oncorhynchus spp. have been most pronounced in the southern extent of their range, and numerous anthropogenic stressors and natural drivers have been identified as potential causes. Using a paleolimnological approach, we have reconstructed the natural variability in the population dynamics of endangered Snake River sockeye salmon O. nerka over approximately the past 1,370 years. The rearing habitat ecology of their main production system, Redfish Lake, Idaho was also assessed over the past 500 years. Siliceous algal remains (diatoms and chrysophytes), stable nitrogen isotope δ15N, cladoceran zooplankton subfossils, and other proxy indicators archived in dated lake sediment cores were employed in this analysis. The inferred natural salmon production was much higher than that recorded in fisheries escapement data. Unprecedented declines in Snake River sockeye salmon production and changes in rearing system ecology were inferred over the past 150 years. The early, negative influences of the Columbia River commercial salmon harvest (in the 1860s) and sustained interruption of migration access (1910‐1934) from hydroelectric damming were evident. Enhanced zooplanktivory, associated with nonnative stocking and possible expansion of kokanee (lacustrine sockeye salmon) beginning in the 1920s and 1930s, appear to have altered the forage base for juvenile sockeye salmon, probably contributing to further declines. Lake nutrient enrichment since the 1950s was inferred, which changed nursery lake nutrient and trophic dynamics. This study highlights both site‐specific and regional influences on declines in past Snake River sockeye salmon population abundance and changes in rearing system ecology for these fish over the past 150 years. Such a long‐term ecological perspective is important to the continued conservation and management of this endangered species and has broader applications for other sockeye salmon runs at risk throughout their range.

Virulence Comparisons of Infectious Hematopoietic Necrosis Virus U and M Genogroups in Sockeye Salmon and Rainbow Trout.

Infectious hematopoietic necrosis virus (IHNV) is an aquatic rhabdovirus that infects salmonids in the Pacific Northwest of the United States, Europe, and Asia. Isolates of IHNV have been phylogenetically classified into three major viral genogroups, designated U, M, and L. To characterize virulence of IHNV in the context of these three viral genogroups, seven strains of IHNV (three U genogroup strains, three M strains, and one L strain) were compared for their pathogenicity in juvenile sockeye salmon Oncorhynchus nerka, kokanee (lacustrine sockeye salmon), and rainbow trout O. mykiss. Fish were waterborne-exposed to the different viral strains, and virulence was assessed by comparing mortality curves and final cumulative percent mortality (CPM) in both species of fish at 10°C and 15°C. In sockeye salmon and kokanee, the U genogroup virus types were extremely virulent, causing average CPMs of 69-100%, while the M genogroup virus types caused very little or no mortality (CPM = 0-4%). The endangered Redfish Lake sockeye salmon stock exhibited extreme differences in susceptibility to the U and M genogroups. Conversely, in two stocks of rainbow trout, the M genogroup virus types were more virulent, inducing average CPMs of 25-85%, while the U genogroup viruses caused lower mortality (CPM = 5-41%). In both fish species, the single L genogroup strain caused low to intermediate mortality (CPM = 13-53%). Viral glycoprotein sequence comparisons of the seven challenge strains revealed three amino acid sites (247, 256, and 270) that consistently differed between the U and M genogroups, possibly contributing to pathogenicity differences.

Estimation of nitrogen stable isotope turnover rate of Oncorhynchus nerka

Estimation of the isotopic turnover rate in the tissues of organisms allows us to estimate the temporal relationship between the isotope ratio of an organism and its prey, and to analyze seasonal variations of food webs and migratory patterns of animals. We analyzed the isotopic turnover rate in the tissue of lacustrine sockeye salmon, Oncorhynchus nerka, of three age classes in a laboratory food alteration experiment to clarify the isotopic turnover rate. The contribution of growth to isotopic turnover was higher in young and fast-growing lacustrine sockeye salmon than in older and slow-growing fish. Maturation masks the relationship between the contributions of growth and metabolism to isotopic change. Our estimate of the isotopic time lag of lacustrine sockeye salmon can be used to research trophic relationships of anadromous sockeye salmon.

Immunohistochemical demonstration of salmon olfactory glutathione S-transferase class pi (N24) in the olfactory system of lacustrine sockeye salmon during ontogenesis and cell proliferation.

In mammals, glutathione S-transferase (GST) in the olfactory epithelium is involved in assistance of the olfactory reception by the xenobiotic metabolism. We previously reported the protein and gene expressions of salmon olfactory GST class pi (soGST) in the olfactory receptor cells (ORCs) of the salmonid fish. However, the chronological appearances of soGST in ORCs during ontogeny and cell proliferation are still unknown in this species. In this study, we performed immunohistochemistry of soGST using an antibody specific to soGST in the olfactory system (olfactory placode, olfactory pit, olfactory epithelium, olfactory nerve and olfactory bulb) of lacustrine sockeye salmon ( Oncorhynchus nerka) embryos and 5-bromo-2'-deoxyuridine (BrdU) experimental fish. The projection of olfactory nerve bundles from the olfactory pit to the presumptive olfactory bulb was identified at embryonic day 28 after fertilization. The olfactory cilia were first detected on the apical surface of ORCs at day 43. soGST-immunoreactivity was first detected within the olfactory pit cells at day 55. At 58 day, the number of soGST-immunoreactive cells increased markedly in the olfactory epithelia, and soGST-immunoreactive fibers were observed in the olfactory nerves and olfactory bulbs. By in vivo uptake of BrdU in 1-year-old fish, we observed for the first time at day 7 after labeling that the olfactory epithelia showed ORCs in which both soGST-immunoreactivity and BrdU coexisted. These results indicate that soGST is synthesized in the mature ORCs of lacustrine sockeye salmon after cell formation and differentiation.

Winter Ecology of Kokanee: Implications for Salmon Management

AbstractWe sampled various limnological parameters and measured growth and diet of age‐0 kokanee Oncorhynchus nerka (lacustrine sockeye salmon) during two winters in a high‐mountain lake of the Sawtooth Valley, Idaho. Although winter has been recognized as an important period for many warmwater fishes and for stream‐dwelling salmonids, winter limitations have only recently been studied for coolwater and coldwater species. Ice and snow cover in winter limited light penetration. As a result, chlorophyll‐a and zooplankton density were lower in ice‐covered periods than during ice‐free periods. The weight of stomach contents was often below a maintenance ration, yet the incidence of empty stomachs was extremely low (1 of 63) and the weight of stomach contents increased as energy reserves declined, indicating that kokanee were actively foraging during winter. Kokanee length and weight remained constant during the winter of 1993–1994 but increased from November through May in 1994–1995. Condition factors, however, declined significantly over the winter in both years, and lipid content approached levels associated with mortality. Differences in growth patterns may have been caused by a combination of changes in zooplankton density and kokanee abundance and in kokanee behavior to defend energy reserves or avoid predation. Results demonstrated the ambiguity of some growth measurements and the importance of choosing the correct metric for measuring growth in fishes. Because juvenile kokanee and sockeye salmon are ecologically similar, management efforts to restore the endangered Snake River sockeye salmon to the Sawtooth Valley lakes should recognize that winter conditions might be a bottleneck for this species.