Post-spawn migrations of hatchery-origin Oncorhynchus mykiss kelts in the Central Valley of California

We used acoustic telemetry to study the post-spawn movement of Oncorhynchus mykiss kelts released in April 2005 and 2006 from the Coleman National Fish Hatchery, Anderson, CA. Following release, O. mykiss kelts demonstrated both anadromous and non-anadromous life histories, with some fish alternating life history strategies between years. Anadromy was most common, characterized by a short-term residence near the release site, followed by sustained downstream emigration once initiated. O. mykiss kelts demonstrating anadromy arrived at the Golden Gate Bridge from April to mid-July. Repeat spawning migrations of anadromous O. mykiss kelts began from late-September through October of the year of release. High fidelity back to Battle Creek was observed, occurring from late-September through November. While most O. mykiss kelts were anadromous, at least 10 % remained in freshwater, or residualized. O. mykiss kelts that residualized demonstrated two distinct patterns of movement: 1) residency near the release location, and 2) potamodromy. Overall survival was high with 36 % and 48 % of O. mykiss kelts released making a repeat spawning migration and demonstrating iteroparity in 2005 and 2006, respectively. Increase in body lengths of O. mykiss kelts that returned to the Coleman NFH were significantly greater for anadromous fish, compared to fish that residualized, but survival was higher for fish that residualized. Release of hatchery O. mykiss kelts could result in both positive and negative genetic and ecological effects to hatchery- and naturally-producing salmonids. We believe the benefits of releasing O. mykiss kelts at the Coleman NFH, including increased numbers and size of fish in the recreational fishery and genetic and demographic benefits to the hatchery brood stock outweigh the limited risk to natural populations that would result from predation and competition of the relatively small number of O. mykiss kelts that resided in fresh water.     

Archival and acoustic tags reveal the post-spawning migrations, diving behavior, and thermal habitat of hatchery-origin Sacramento River steelhead kelts (Oncorhynchus mykiss)

Acoustic and geolocating archival tags were deployed on steelhead kelts to study their post-spawning migrations, diving behavior and thermal habitat. Fourteen reconditioned steelhead kelts were surgically implanted with LAT2510 archival and V7-2 L acoustic tags, and released from Coleman National Fish Hatchery. An array of acoustic receivers in the Sacramento River and Delta, and the San Francisco Bay estuary detected the downstream movement of the steelhead. Two steelhead kelts (J and M) with archival tags were recovered at the hatchery after 219 and 285 days at liberty respectively. Based on changes in geolocations, vertical movements, and water temperatures, the migrations of steelhead J and M were divided into five and six phases respectively. Steelhead J moved into coastal California waters while steelhead M remained in freshwater for the majority of its time at liberty. Large increases in temperature and opacity were recorded before and after the ocean phases, likely as the steelhead moved through the Sacramento Delta. Both steelhead kelts remained relatively close to the surface throughout their migration but there were diurnal differences in the vertical movements. In freshwater, the steelhead tended to be deeper during the day (e.g., steelhead J: 3.08?±?1.50 vs 1.65?±?1.15 m, day vs night) but in the ocean, the steelhead were typically deeper during the night (1.32?±?1.61 vs 5.63?±?6.11 m). Both steelhead kelts appeared to be less oceanic than a previous study in Scott Creek, a small coastal stream approximately 100 km south of the mouth of San Francisco Bay. Although this study has a small sample size, the results suggest that steelhead kelts from a large river and estuary system, like the Sacramento River, may be relatively less oceanic than steelhead kelts from small coastal streams.     

Signatures of natural selection among lineages and habitats in Oncorhynchus mykiss

Recent advances in molecular interrogation techniques now allow unprecedented genomic inference about the role of adaptive genetic divergence in wild populations. We used high-throughput genotyping to screen a genome-wide panel of 276 single nucleotide polymorphisms (SNPs) for the economically and culturally important salmonid Oncorhynchus mykiss. Samples included 805 individuals from 11 anadromous and resident populations from the northwestern United States and British Columbia, and represented two major lineages including paired populations of each life history within single drainages of each lineage. Overall patterns of variation affirmed clear distinctions between lineages and in most instances, isolation by distance within them. Evidence for divergent selection at eight candidate loci included significant landscape correlations, particularly with temperature. High diversity of two nonsynonymous mutations within the peptide-binding region of the major histocompatibility complex (MHC) class II (DAB) gene provided signatures of balancing selection. Weak signals for potential selection between sympatric resident and anadromous populations were revealed from genome scans and allele frequency comparisons. Our results suggest an important adaptive role for immune-related functions and present a large genomic resource for future studies.     

Gene Flow between Sympatric Life History Forms of Oncorhynchus mykiss Located above and below Migratory Barriers

Oncorhynchus mykiss have a diverse array of life history types, and understanding the relationship among types is important for management of the species. Patterns of gene flow between sympatric freshwater resident O. mykiss, commonly known as rainbow trout, and anadromous O. mykiss, commonly known as steelhead, populations are complex and poorly understood. In this study, we attempt to determine the occurrence and pathways of gene flow and the degree of genetic similarity between sympatric resident and anadromous O. mykiss in three river systems, and investigate whether resident O. mykiss are producing anadromous offspring in these rivers, two of which have complete barriers to upstream migration. We found that the population structure of the O. mykiss in these rivers appears to be influenced more by the presence of a barrier to upstream migration than by life history type. The sex ratio of resident O. mykiss located above a barrier, and smolts captured in screw traps was significantly skewed in favor of females, whereas the reverse was true below the barriers, suggesting that male resident O. mykiss readily migrate downstream over the barrier, and that precocious male maturation may be occurring in the anadromous populations. Through paternity analyses, we also provide direct confirmation that resident O. mykiss can produce offspring that become anadromous. Most (89%) of the resident O. mykiss that produced anadromous offspring were males. Our results add to the growing body of evidence that shows that gene flow does readily occur between sympatric resident and anadromous O. mykiss life history types, and indicates that resident O. mykiss populations may be a potential repository of genes for the anadromous life history type.     

Tissue-specific distribution patterns of retinoids and didehydroretinoids in rainbow trout Oncorhynchus mykiss

Retinoids (vitamin A) are known to be involved in many key biological functions in mammals, such as embryonic development, reproduction or vision. Besides standard vitamin A forms, freshwater fish tissues contain high levels of didehydroretinoids or vitamin A₂ forms. However, the tissue distribution, metabolism and function of both standard and particularly the didehydroretinoids are still poorly known in fish. In this study, we have quantified the levels of retinoids, including retinol, retinaldehyde, retinyl palmitate and their corresponding didehydro forms, as well as the levels of the active polar retinoids all-trans-, 9-cis- and 13-cis-retinoic acid in distinct tissues of juvenile rainbow trout. Our results indicate that the liver is clearly the main retinoid storage tissue in juvenile rainbow trout. Didehydroretinoids were dominant over retinoids in all analyzed tissues with the exception of plasma. Additionally, significant differences among tissues were observed between retinoids and didehydroretinoids, such as differences in the ester profiles and the proportions between free and esterified forms, suggesting that mechanisms that favor the utilization or storage of one of the other groups of compounds might exist in fish. Our data also show the presence of polar retinoids in different tissues of fish at the fmol/g scale. Overall, this study clearly demonstrates the presence of tissue-specific patterns of accumulation of both polar and nonpolar retinoids in fish tissues. The biological relevance of these findings should be the focus of future studies.     

Survival and movement patterns of central California coast native steelhead trout (Oncorhynchus mykiss) in the Napa River

Drawing on acoustic telemetry this study identifies and describes local and regional scale survival and movement patterns of Central California Coast steelhead (Oncorhynchus mykiss), including their potential utilization of newly restored tidal marsh habitats in the Napa River system. Between April 8th and May 5th of 2010, 20 steelhead smolts ranging in fork length from 164 to 305 mm were collected, tagged with acoustic transmitters, and released in the upper Napa River (above tidal influence). We found no effect of release date (P?<?0.001) or size (P?<?0.005) on survival estimates based on model likelihoods. Cumulative survival from smolt release location to the Golden Gate Bridge over approximately 77 river kilometers (RKM) was 0.60 (SE?=?0.16). Reach-specific survival was lowest in the initial 30 km reach (0.70 SE?=?0.1). Survival was higher in San Pablo Bay (0.89 SE?=?0.1) and San Francisco Bay (0.96 SE?=?0.2). Sixty percent of the fish that entered the ocean were detected on a line of acoustic monitors at Point Reyes approximately 60 km north of the Golden Gate. Average movement rates of smolts were highest in San Pablo Bay (36.6 km?d^-1 SE?=?3.3) and San Francisco Bay (28.9 km?d^-1 SE?=?6.6). Smolts migrated more slowly in the river (9.0 km?d^-1 SE?=?0.9) and ocean (4.1 km?d^-1 SE?=?1.2). However, smolt movement rates in the river were dependent on location. Average movement rates of smolts were greatest shortly before their exit from the Napa River (83 km?d^-1 SE?=?13.2). Fish were not detected within the recently reconnected former salt production ponds (North, Central, and South units) adjacent to the Napa River. Based on the detection patterns of fish throughout the study area, it appears that most fish were moving at relatively high rates and were not exploring off-channel habitat.     

Melanin-based Feather Colour and Moulting Latitude in a Migratory Songbird

Melanins are common pigments used for colouration in animal tissue and recent evidence suggests that they may be condition-dependent signals used in mate choice. We examined the hypothesis that individuals moulting during migration produce relatively dull feathers compared to individuals moulting on the breeding grounds prior to migration because of the costs associated with overlapping these two activities. We estimated both the colour and moulting latitude of melanin-based feathers in barn swallows ( Hirundo rustica ). Moulting latitude was inferred from stable-hydrogen isotope (δD) values of individuals that were known to have bred at the same site the previous year. Contrary to expectations, δD values in feathers suggested that most, if not all, individuals moulted their feathers south of the breeding grounds. Furthermore, we found that males moulting at southern latitudes tended to produce darker, more rufous coloured throat feathers compared to males moulting at more northern latitudes, closer to the breeding grounds. However, we found no such relationship in females. Males could face a trade-off between growing new but relatively dull feathers before or just after the commencement of migration versus waiting to grow more rufous coloured feathers well into fall migration or on the wintering grounds. We suggest that this trade-off could produce an honest signal of male quality if only high quality males can afford to migrate large distances on feathers that are greater than a year old.     

Altered burst swimming in rainbow trout Oncorhynchus mykiss exposed to natural and synthetic oestrogens

Juvenile rainbow trout Oncorhynchus mykiss were exposed to two concentrations each of 17β‐oestradiol (E2; natural oestrogen hormone) or 17α‐ethinyl oestradiol (EE2; a potent synthetic oestrogen hormone) to evaluate their potential effects on burst‐swimming performance. In each of six successive burst‐swimming assays, burst‐swimming speed (U_burst) was lower in fish exposed to 0·5 and 1 µg l^?1 E2 and EE2 for four days compared with control fish. A practice swim (2 days prior to exposure initiation) in control fish elevated initial U_burst values, but this training effect was not evident in the 1 µg l^?1 EE2‐exposed fish. Several potential oestrogen‐mediated mechanisms for U_burst reductions were investigated, including effects on metabolic products, osmoregulation and blood oxygen‐carrying capacity. Prior to burst‐swimming trials, fish exposed to E2 and EE2 for 4 days had significantly reduced erythrocyte numbers and lower plasma glucose concentrations. After six repeated burst‐swimming trials, plasma glucose, lactate and creatinine concentrations were not significantly different among treatment groups; however, plasma Cl^? concentrations were significantly reduced in E2‐ and EE2‐treated fish. In summary, E2 and EE2 exposure altered oxygen‐carrying capacity ([erythrocytes]) and an osmoregulatory‐related variable ([Cl^?]), effects that may underlie reductions in burst‐swimming speed, which will have implications for fish performance in the wild.     

Opsonizing properties of natural antibodies of rainbow trout, Oncorhynchus mykiss (Walbaum)

In order to confirm previous observations in which a protective effect of rainbow trout natural antibodies against furunculosis was suspected, phagocytosis studies wereconducted in vitro , using combinations of rainbow trout sera with high or low levels of natural antibodies and active or inactivated complement as opsonizing factors. Opsonization was observed in all the cases where complement was present, and to a lesser degree with sera containing only natural antibodies. The results confirm the prime importance of the complement system and provide additional evidence for a possible role of natural antibodies in antimicrobial defences.     

Genomics facilitates evaluation and monitoring of McCloud River Redband Trout (Oncorhynchus mykiss stonei)

The McCloud River Redband Trout (MRRT; Oncorhynchus mykiss stonei) is a unique subspecies of rainbow trout that inhabits the isolated Upper McCloud River of Northern California. A major threat to MRRT is introgressive hybridization with non-native rainbow trout from historical stocking and contemporary unauthorized introductions. To help address this concern, we collected RAD-sequencing data on 308 total individuals from MRRT and other California O. mykiss populations and examined population structure using Principal Component and admixture analyses. Our results are consistent with previous studies; we found that populations of MRRT in Sheepheaven, Swamp, Edson, and Moosehead creeks are nonintrogressed. Additionally, we saw no evidence of introgression in Dry Creek, and suggest further investigation to determine if it can be considered a core MRRT conservation population. Sheepheaven Creek was previously thought to be the sole historical lineage of MRRT, but our analysis identified three: Sheepheaven, Edson, and Dry creeks, all of which should be preserved. Finally, we discovered diagnostic and polymorphic SNP markers for monitoring introgression and genetic diversity in MRRT. Collectively, our results provide a valuable resource for the conservation and management of MRRT.

     

Ocean migration and behavior of steelhead Oncorhynchus mykiss kelts from the Situk River,Alaska

Environmental Biology of Fishes - Although steelhead (Oncorhynchus mykiss) is an iconic species found throughout the North Pacific rim, little is known about its ocean ecology. To provide insights...     

Migratory Patterns of Wild Chinook Salmon Oncorhynchus tshawytscha Returning to a Large,Free-Flowing River Basin

Upriver movements were determined for Chinook salmon Oncorhynchus tshawytscha returning to the Yukon River, a large, virtually pristine river basin. These returns have declined dramatically since the late 1990s, and information is needed to better manage the run and facilitate conservation efforts. A total of 2,860 fish were radio tagged during 2002–2004. Most (97.5%) of the fish tracked upriver to spawning areas displayed continual upriver movements and strong fidelity to the terminal tributaries entered. Movement rates were substantially slower for fish spawning in lower river tributaries (28–40 km d^-1) compared to upper basin stocks (52–62 km d^-1). Three distinct migratory patterns were observed, including a gradual decline, pronounced decline, and substantial increase in movement rate as the fish moved upriver. Stocks destined for the same region exhibited similar migratory patterns. Individual fish within a stock showed substantial variation, but tended to reflect the regional pattern. Differences between consistently faster and slower fish explained 74% of the within-stock variation, whereas relative shifts in sequential movement rates between “hares” (faster fish becoming slower) and “tortoises” (slow but steady fish) explained 22% of the variation. Pulses of fish moving upriver were not cohesive. Fish tagged over a 4-day period took 16 days to pass a site 872 km upriver. Movement rates were substantially faster and the percentage of atypical movements considerably less than reported in more southerly drainages, but may reflect the pristine conditions within the Yukon River, wild origins of the fish, and discrete run timing of the returns. Movement data can provide numerous insights into the status and management of salmon returns, particularly in large river drainages with widely scattered fisheries where management actions in the lower river potentially impact harvests and escapement farther upstream. However, the substantial variation exhibited among individual fish within a stock can complicate these efforts.     

Steroid enzyme gene expressions during natural and androgen-induced gonadal differentiation in the rainbow trout, Oncorhynchus mykiss.

In fish, according to Yamamoto's model, androgens would drive testis differentiation and estrogens ovarian differentiation. In order to study the implication of steroid enzymes in rainbow trout gonadal differentiation, we examined the expression of some steroid enzyme genes during natural differentiation (cholesterol side chain cleavage = P450scc, 17-hydroxylase/lyase = P450c17, 3beta-hydroxysteroid dehydrogenase = 3betaHSD) and androgen-induced differentiation (P450scc, P450c17, 3betaHSD, aromatase = P450aro, and 11beta-hydroxylase = P45011beta). Expressions of P450scc, 3betaHSD, and P450c17 were all detected in male and female gonads at 55 days post-fertilization (dpf), i.e., two weeks before histological differentiation. There were no differences in their expression level respective to the sex. The androgen treatment was carried out by administration of 11beta-hydroxyandrostenedione (11betaOHDelta4) in genetic all-female populations and the resulting sex ratios were found to be 100% male even at a low dosage of 1 mg/kg of food. Following 11betaOHDelta4 treatment, only the expression of P450c17 was found to be sustained when compared with the female untreated control. In contrast, P450scc was clearly up-regulated and 3betaHSD and P450aro down-regulated by the androgen treatment. P45011beta gene expression remained low in gonads of androgen-treated females, as it did in control untreated females. These results together demonstrate that steroidogenesis in rainbow trout is potentially active in pre-differentiating gonads of both sexes, and that one of the masculinizing actions of androgens in the species may be to down-regulate the female-specific gonadal P450aro gene expression. However, in vivo androgen treatment in genetic females does not induce the same pattern of steroid gene expression as in genetic males. These data suggest that exogenous androgens might induce a male differentiation process with P450aro inhibition being one of the steps required. However, this process would not involve endogenously produced 11-oxygenated androgens.     

Anorexia reduces the severity of cryptobiosis in Oncorhynchus mykiss

Cryptobia salmositica multiplied more rapidly and caused a more severe disease with a higher mortality (65%) in rainbow trout (Oncorhynchus mykiss) fed a 52% protein diet than in fish fed 37 or 22% protein diets (25 and 30% mortalities, respectively). Also, plasma protein was significantly higher in fish fed a 52% protein diet than in fish fed 37 or 22% protein diets. Anorexia in infected trout was related positively to parasitemia and was most significant at 4 wk postinfection. During the chronic phase of the infection, food consumption increased with declining parasitemia. It is hypothesized that anorexia lowers plasma protein level, which reduces the multiplication rate of parasites, thus decreasing the severity of the disease.     

The genetic basis of smoltification-related traits in Oncorhynchus mykiss

The timing and propensity for migration between fresh- and seawater is a key theme in the diversity of life histories within the salmonid fishes. Across salmonid species, life-history strategies range from wholly freshwater-resident populations, to migratory and nonmigratory variation within populations, to populations and species that are primarily migratory. Despite the central theme of migration to the evolution of these fishes, the genetic architecture of migration-related processes is poorly understood. Using a genetic cross of clonal lines derived from migratory and nonmigratory life-history types of Onchorhynchus mykiss (steelhead and rainbow trout, respectively), we have dissected the genetic architecture of the complex physiological and morphological transformation that occurs immediately prior to seaward migration (termed smoltification). Quantitative trait loci (QTL) analyses were used to identify the number, effects, and genomic location of loci associated with smoltification-related traits, including growth and condition factor, body coloration, morphology, and osmoregulatory enzymes during the smoltification period. Genetic analyses revealed numerous QTL, but one locus in particular is associated with multiple traits in single and joint analyses. Dissecting the genetic architecture of this highly complex trait has profound implications for understanding the genetic and evolutionary basis of life-history diversity within and among migratory fishes.     

Behavioural variation between piscivore and insectivore rainbow trout Oncorhynchus mykiss

A proactive-reactive continuum integrating multiple (i.e., 3+) dimensions of animal behaviour has been reported as a major axis of behavioural differentiation, but its stability along a biological hierarchy from individuals to populations remains speculative. Piscivore and insectivore rainbow trout (Oncorhynchus mykiss) represent closely related ecotypes with strong ecological divergence driven by selection for a large-bodied piscivorous lifestyle with fast juvenile growth vs. selection for smaller adult body size and lower growth associated with an insectivorous diet. To evaluate whether differences in behaviour between ecotypes are consistent with a proactive-reactive axis and consistent along a biological hierarchy, the authors examined variation in emergence time from a shelter, exploration, activity and predator inspection among individuals, populations and ecotypes of juvenile piscivore and insectivore rainbow trout O. mykiss. As expected, the faster-growing piscivore ecotype was more proactive (i.e., shorter emergence time, exploration and predator inspection) than the more reactive insectivore ecotype. This behavioural contrast was partly maintained across populations, although activity differences were most pronounced among populations, rather than emergence time. Insectivore fry showed substantial variation in behavioural expression among individuals within populations; by contrast, piscivores showed highly similar proactive behaviours with significantly lower inter-individual variation in behavioural expression, suggesting intense selection on behaviour supporting their faster growth. This work suggests that piscivore and insectivore O. mykiss broadly differ in behaviour along a proactive vs. reactive continuum, and highlights the greater multidimensionality of behavioural expression within the insectivore ecotype. Contrasting behaviours between ecotypes may result from differential selection for slow vs. fast juvenile growth and associated metabolism, and may contribute to adult trophic specialization.     

Electrophoretic patterns of yolk proteins throughout ovarian development and their relationship to vitellogenin in the rainbow trout,Oncorhynchus mykiss

• 1.1. Electrophoretic patterns of yolk proteins were investigated throughout ovarian development and their relationship to vitellogenin determined in a pulse-chase experiment with ³H-vitellogenin.
• 2.2. Using a radioimmunoassay for vitellogenin, vitellogenin/yolk protein products of vitellogenin were detected in follicles throughout ovarian development and in ovulated eggs.
• 3.3. The majority of yolk proteins in follicles measuring less than 1.0 mm in diameter appeared to be derived from sources other than vitellogenin. In contrast, in the larger follicles all of the major yolk proteins detected were derived from vitellogenin.
• 4.4. Pulse-chase with ³H-vitellogenin revealed that all of the major yolk proteins in 3.0 mm follicles were derived from vitellogenin. The major peptides eluted with molecular masses of 110 and 30 kDa under non-reducing conditions (these are very likely to represent lipovitellin 1 and lipovitellin 2), and 88, 22, 16, and 12 kDa under reducing conditions.
• 5.5. There were no apparent differences in the major yolk proteins in ovulated eggs compared to those in vitellogenic follicles, indicating that no extensive proteolysis of these proteins had occurred during maturation and/or ovulation.

     

Interannual variation of reach specific migratory success for Sacramento River hatchery yearling late-fall run Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss)

The release of hatchery reared salmonid smolts is a common management tool aimed at enhancing depleted wild stocks and maintaining fisheries throughout Northern California and the Pacific Northwest. In the Sacramento River watershed, smolts must migrate through the river, delta and estuary in order to successfully reach the Pacific Ocean. Migration success (success defined as apparent survival from one monitor location to another) may vary between species, year and habitat. We released 500 late-fall run Chinook salmon and 500 steelhead smolts in 2009 and 2010 in the Sacramento River (river kilometer 207). Each smolt was implanted with a coded ultrasonic tag, which was detected by an array of over 300 underwater receiver stations deployed throughout the system. Less than 25 % of fish migrated successfully to the Pacific Ocean in both years. We found that reach specific success was greater in the Delta in 2009 (>60 %) than in 2010 (<33 %), whereas this pattern was reversed in the Bay (<57 % in 2009, >75 % in 2010). Identifying the location, timing and causes of smolt mortality can lead to improved management of the resource.