Precocious Male Maturation Research Articles

The effect of reducing dietary lipid and food availability on precocious male maturation in Chinook Salmon: A production‐scale hatchery experiment

AbstractObjectiveAge of maturation in Chinook Salmon Oncorhynchus tshawytscha is phenotypically plastic, influenced by both genotype and environmental factors, including the availability and composition of the diet. Salmon hatchery programs often rear fish under accelerated growth regimes using high‐lipid diets that can result in earlier age at maturity, including increased prevalence of age‐2 males (minijacks). The goal of this investigation was to compare alternative dietary regimes to mitigate for this shift in age at maturity in hatchery‐reared Umatilla River fall Chinook Salmon.MethodsJuvenile fish were reared at Bonneville Hatchery, Oregon, under four dietary treatments across four replicate brood years. Dietary treatments included two feeding frequencies (standard [fed 7 days/week] and reduced [fed 4 days/week]) and two dietary lipid levels (standard [18%] and reduced [12%]) in a 2 × 2 factorial design. Dietary treatments were applied for approximately 9 months, beginning in March (a month after fry emergence) and lasting until December of the first year, after which all fish were reared on the standard feeding regime (7 days–18%) until the time of release the following spring as yearlings.ResultWe observed significant interannual variation in the proportion of minijacks produced among dietary treatments. For all brood years, decreasing the feeding frequency from 7 to 4 days/week reduced the proportion minijacks by 35.9%, and lowering dietary lipid from 18% to 12% reduced the proportion minijacks by 30%. The combined effects of reducing the feeding frequency and lowering dietary lipid were additive, reducing the proportion minijacks by 65.5% compared to the standard rearing regime. Growth and energetic indices were monitored throughout and confirmed findings from previous laboratory‐based studies indicating that physiological status 10–12 months prior to spawn timing is important for the “decision” to mature.ConclusionResults of this investigation provide useful insights for optimizing rearing regimes for the Umatilla River program and other Chinook Salmon hatchery programs.

Pituitary Gonadotropin Gene Expression During Induced Onset of Postsmolt Maturation in Male Atlantic Salmon: In Vivo and Tissue Culture Studies.

Precocious male maturation causes reduced welfare and increased production costs in Atlantic salmon (Salmo salar) aquaculture. The pituitary produces and releases follicle-stimulating hormone (Fsh), the gonadotropin triggering puberty in male salmonids. However, little is known about how Fsh production is regulated in Atlantic salmon. We examined, in vivo and ex vivo, transcriptional changes of gonadotropin-related genes accompanying the initial steps of testis maturation, in pituitaries of males exposed to photoperiod and temperature conditions promoting maturation (constant light and 16°C). Pituitary fshb, lhb and gnrhr2bba transcripts increased in vivo in maturing males (gonado-somatic index > 0.1%). RNA sequencing (RNAseq) analysis using pituitaries from genetically similar males carrying the same genetic predisposition to mature, but differing by responding or not responding to stimulatory environmental conditions, revealed 144 differentially expressed genes, ~2/3rds being up-regulated in responders, including fshb and other pituitary hormones, steroid-related and other puberty-associated transcripts. Functional enrichment analyses confirmed gene involvement in hormone/steroid production and gonad development. In ex vivo studies, whole pituitaries were exposed to a selection of hormones and growth factors. Gonadotropin-releasing hormone (Gnrh), 17β-estradiol (E2) and 11-ketotestosterone (11-KT) up-regulated gnrhr2bba and lhb, while fshb was up-regulated by Gnrh but down-regulated by 11-KT in pituitaries from immature males. Also pituitaries from maturing males responded to Gnrh and sex steroids by increased gnrhr2bba and lhb transcript levels, but fshb expression remained unchanged. Growth factors (inhibin A, activin A and insulin-like growth factor 1) did not change gnrhr2bba, lhb or fshb transcript levels in pituitaries either from immature or maturing males. Additional pituitary ex vivo studies on candidates identified by RNAseq showed that these transcripts were preferentially regulated by Gnrh and sex steroids, but not by growth factors, and that Gnrh/sex steroids were less effective when incubating pituitaries from maturing males. Our results suggest that a yet to be characterized mechanism up-regulating fshb expression in the salmon pituitary is activated in response to stimulatory environmental conditions prior to morphological signs of testis maturation, and that the transcriptional program associated with this mechanism becomes unresponsive or less responsive to most stimulators ex vivo once males had entered pubertal developmental in vivo.

Precocial male maturation contributes to the introgression of farmed Atlantic salmon into wild populations

The escape of domesticated Atlantic salmon Salmo salar from aquaculture facilities represents a continued threat to the genetic and demographic stability of wild salmon stocks. Escaped farm-origin salmon have been shown to hybridize with wild conspecifics, yet the long-term genetic impacts are generally unknown. Theoretically, life history variation, specifically precocial maturation of male hybrids, could fast-track introgression, but evidence for this has been sparse. Here, we used empirical and experimental data to examine the role of precocious male maturation in introgression. We examined hybrid class composition using juvenile sampling and genetic assignment over a 5 yr period following an escape event in southern Newfoundland, a region with high rates of natural male precocial maturation. Initially following the escape, the proportion of first-generation (F1) hybrids was high and then decreased annually, contrasting the proportion of backcross wild individuals, which increased over time. The presence and temporal distribution of backcross wild individuals supports the hypothesis that high rates of precocial maturation can fast-track the long-term impacts of escaped farmed salmon on wild populations via interbreeding. This was experimentally tested using lab-created wild, farmed, and F1 parr released and recaptured from a Newfoundland river to assess levels of precocious male maturation. Observed rates of maturation of F1 hybrids were high and similar to wild parr (77 vs. 73%, respectively), indicating that most F1 hybrids mature precocially. Our results suggest that rates of precocial male maturation should be explicitly considered in risk assessments evaluating the genetic impacts of escaped farmed salmon on wild populations.

Precocious Maturation in Spring‐Run Chinook Salmon Is Affected by Incubation Temperature, Feeding Regime, and Parentage

AbstractSalmonid populations of the Central Valley of California have been in decline for decades, making hatchery practices that combine conservation strategies with targeted research essential to optimize recruitment to adulthood. Hatchery populations generally exhibit a higher incidence of precocious male maturation than natural populations. However, optimal hatchery management practices pertaining to incubation, feeding, and genetic predisposition have yet to be optimized to lower the incidence of precocity in hatchery‐reared male spring‐run Chinook Salmon Oncorhynchus tshawytscha. To further assess this, we conducted a 2 × 2 factorial experiment exploring the effect of embryo incubation temperature (cold or warm) and post‐ponding ration (high or low) on incidence of age‐1 precocious male maturation. Fertilized eggs from each parental cross were placed among each treatment group to control for genetic variation and track any genetic predisposition. Precocity rate at year 1 was affected by incubation temperature and feed rate. There were also significant differences in growth rate and body condition among the treatment groups during early development. Additionally, the precocious males were nonrandomly produced by the crosses, suggesting a significant parentage effect on precocity. Optimization of Chinook Salmon rearing techniques is critical—not only to lessen the incidence of precocity and identify the causal parameters, but also to maximize successful reintroduction.

Dietary tetradecylthioacetic acid supplementation during the fall prevents an increase in body lipid levels but does not influence precocious male maturation rate in juvenile spring Chinook salmon

Precocious maturation of male fish as two-year-olds occurs at significant rates in spring Chinook salmon hatchery programmes in the Columbia River Basin, representing a loss of production. Precocious maturation is thought to occur due to elevated lipid and other energy reserves in hatchery fish during critical periods for the regulation of gonadal development. To determine whether modification of lipid reserves affects precocious maturation rates in juvenile spring Chinook salmon, we administered feed supplemented with tetradecylthioacetic acid (TTA; a supplement that upregulates lipid oxidation) during the fall critical period one year prior to maturation of precocious individuals. Maturation status was determined the following spring from plasma 11-ketotestosterone levels. TTA administration reduced body lipid levels relative to controls but did not reduce precocious maturation rate. Fish growth was reduced during the TTA feeding period but recovered after fish were returned to a standard diet. No differences in the effect of TTA were found between male and female fish. Our results show that TTA can be used to manipulate body lipid levels in juvenile Chinook salmon but provide no support for a major role of fall body lipid levels in regulating precocious maturation in juvenile male spring Chinook salmon under hatchery conditions.

Stock-specific variation in the probability of precocious male maturation in hatchery Chinook salmon (Oncorhynchus tshawytscha)

Age of maturation in many salmonid species is phenotypically plastic and dependent on exceeding a genetically set threshold in growth, often described as a probabilistic maturation reaction norm (PMRN). Hatchery supplementation programs for Chinook salmon (Oncorhynchus tshawytscha) in the Pacific Northwest US have been developed to minimize differences between hatchery and wild fish by integrating natural-origin adults into broodstock, potentially affecting PMRNs. We raised fish from 10 Chinook salmon stocks with variable levels of natural-origin integration in a common garden environment to explore potential genetic variation in PMRNs for precocious male maturation as age 2 minijacks. Proportion minijacks varied ≈10-fold (0.043 to 0.443) and the PMRN WP50 (predicted weight at 50% maturation) varied by ≈18 g (24.1 to 41.7 g). The propensity for minijack maturation was generally higher in stocks with higher levels of natural-origin integration. These findings demonstrate the effect of genotype by environment interactions on life history of salmonids and the need for stock-specific tailoring of rearing regimes to regulate differences between hatchery and wild fish, when wild fish are used in broodstocks.

Evaluation of endocrine and transcriptomic markers of male maturation in winter-run Steelhead Trout (Oncorhynchus mykiss)

Steelhead Trout (Oncorhynchus mykiss) display a varied life-history, including precocious male maturation at age-1 or age-2. In wild fish, precocious male maturation represents an important component of a diverse life-history portfolio. In hatchery programs, however, it is undesirable if rearing practices increase rates of early male maturation and reduce numbers of anadromous male adults. Our study aimed to develop endocrine and molecular markers for identifying males at early stages of maturation in the spring (prior to smolt release) and evaluated the potential use of these markers for quantifying early male maturation rates at a hatchery scale. In a laboratory study, Skookumchuck winter-run Steelhead Trout were reared at a high growth rate in order to increase the occurrence of precocious male maturation. Fish were lethally sub-sampled in February, prior to the time of smolt release; in May, at the time of smolt release; and in September, when 1+ age maturing males that would spawn the following spring were clearly identifiable based solely on gonadosomatic index (GSI). In February and May samples, we measured GSI, plasma 11-ketotestosterone (11KT), mRNAs for pituitary follicle stimulating hormone (fshb) and luteinizing hormone (lhb) beta subunits, and analyzed stage of spermatogenesis by testis histology. Additionally, in May, we measured testis anti-Müllerian hormone (amh) and insulin-like growth factor 3 (igf3) mRNA. Our primary goal was to evaluate the aforementioned maturation indices for their efficacy in forecasting the proportion of fish initiating early male maturation in the spring (approximately 1 year prior to spermiation), compared to the proportion that actually matured. Combining measures of GSI, plasma 11KT, and pituitary fshb and lhb mRNA expression provided a useful, but conservative, estimate of the proportion of males initiating maturation in the spring (21%) compared to the proportion that were ultimately destined to mature (37%) the following spring. These results suggest that maturation may be less synchronous than previously appreciated and some males may have initiated maturation after our census in May.

Maintaining a wild phenotype in a conservation hatchery program for Chinook salmon: The effect of managed breeding on early male maturation.

In many salmonid species, age and size at maturation is plastic and influenced by the interaction between genetic and environmental factors. Hatchery reared salmon often mature at an earlier age and smaller size than wild fish. Modern salmon conservation efforts have focused on managing the level of gene flow between hatchery and natural origin fish to minimize potential genotypic and phenotypic change. In salmonids, maturation probability is dependent on exceeding a genetically set threshold in growth rate and energetic status (and by association, body size) referred to as the probabalisitic maturation reaction norm (PMRN). Over fourteen years, we monitored the frequency of age-2 precocious male maturation (common term: age-2 minijack rate) and the PMRN of natural founder (FNDR), integrated natural-hatchery (INT), and segregated hatchery (SEG) broodlines of spring Chinook salmon, Oncorhynchus tshawytscha. The average age-2 minijack rate (± SEM) of the FNDR, INT and SEG broodlines was 48.2 ± 5.2%, 41.9 ± 3.6% and 30.9 ± 4.7%, respectively. Additionally, the PMRN WP50 (predicted weight at 50% maturation) of the SEG broodline was significantly greater (20.5 g) than that of the FNDR/INT broodlines (18.2 g). We also conducted a common garden experiment exploring the effects of less than one [INT (0–1)], one [SEG (1)] or two [SEG (2)] generations of hatchery culture on the age-2 minijack rate and PMRN WP50. Growth was not significantly different among broodlines, but age-2 minijack rates were significantly lower following two consecutive generations of hatchery culture: [INT (0–1): 68.3 ± 1.7%], [SEG (1): 70.3 ± 1.8%] and [SEG (2): 58.6 ± 0.4%] and the PMRN WP50 was significantly higher by 6.1 g after two generations of SEG culture. These results indicate that managed gene flow reduces phenotypic divergence, but may serve to maintain potentially undesirably high age-2 minijack rates in salmon conservation hatchery programs.

Implications for introgression: has selection for fast growth altered the size threshold for precocious male maturation in domesticated Atlantic salmon?

BackgroundMature male parr (MMP) represent an important alternative life-history strategy in Atlantic salmon populations. Previous studies indicate that the maturation size threshold for male parr varies among wild populations and is influenced by individual growth, environmental conditions, and genetics. More than ten generations of breeding have resulted in domesticated salmon displaying many genetic differences to wild salmon, including greatly increased growth rates. This may have resulted in domesticated fish with the potential to outgrow the size threshold for early maturation, or evolution of the size threshold of the trait itself. To investigate this, we performed a common-garden experiment under farming conditions using 4680 salmon from 39 families representing four wild, two wild-domesticated hybrid, and two domesticated strains.ResultsDomesticated salmon outgrew wild salmon 2–5-fold, and hybrids displayed intermediate growth. Overall, the numbers of MMP varied greatly among families and strains: averaging 4–12% in domesticated, 18–25% in hybrid, and 43–74% in the wild populations. However, when the influence of growth was accounted for, by dividing fish into lower and upper size modes, no difference in the incidence of MMP was detected among domesticated and wild strains in either size mode. In the lower size mode, hybrids displayed significantly lower incidences of mature males than their wild parental strains. No consistent differences in the body size of MMP, connected to domestication, was detected.ConclusionsOur data demonstrate: 1- no evidence for the evolution of the size threshold for MMP in domesticated salmon, 2- the vastly lower incidence of MMP in domesticated strains under aquaculture conditions is primarily due to their genetically increased growth rate causing them to outgrow the size threshold for early maturation, 3- the incidence of MMP is likely to overlap among domesticated and wild salmon in the natural habitat where they typically display overlapping growth, although hybrid offspring may display lower incidences of mature male parr. These results have implications for wild salmon populations that are exposed to introgression from domesticated escapees.

Plasma 11‐Ketotestosterone in Individual Age‐1 Spring Chinook Salmon Males Accurately Predicts Age‐2 Maturation Status

AbstractHigh rates of precocious male maturation of spring Chinook Salmon Oncorhynchus tshawytscha as 2‐year‐old minijacks have been observed in Columbia River basin hatchery programs. Previously, minijack rates have been assessed by lethal sampling during the spring prior to release of the age‐1 smolts and measurement of plasma levels of 11‐ketotestosterone (11‐KT), the major androgen in salmonids. Analysis of plasma 11‐KT levels has been used for separation of male fish into two distinct groups: low levels for immature males and high levels for precociously maturing minijacks. However, no published studies have confirmed how accurately plasma 11‐KT levels measured in the spring prior to smolt release correspond to the maturation status of individual males the following fall spawning season. We utilized both lethal and nonlethal sampling to determine when to sample hatchery‐reared juveniles to obtain clear separation between immature and precociously maturing males and PIT‐tagged fish to determine whether plasma 11‐KT levels in the spring accurately predicted an individual's maturation status in the fall. The distribution of plasma 11‐KT values from fish sampled in February was not significantly bimodal, whereas that from fish sampled in April was strongly bimodal. Plasma 11‐KT levels measured nonlethally in April accurately predicted the maturation status of 99% of male fish, confirmed via the gonadosomatic index obtained the following September. Plasma 11‐KT levels increased from April to September in both immature and maturing males, although the percent increase in maturing males was 10 times greater than that experienced by the non‐maturing smolts. Our findings support the use of spring plasma 11‐KT level as an indicator of maturation status in Chinook Salmon juveniles, provided that an appropriate sampling time is selected.

Use of Morphological and Physiological Indices to Characterize Life History Diversity in Juvenile Hatchery Winter‐Run Steelhead

AbstractSteelhead Oncorhynchus mykiss exhibit significant life history plasticity, including variation in freshwater residence time, age of smoltification, and maturation that are influenced by exceeding specific thresholds in size or body energy stores. Fish that do not reach minimum thresholds for smoltification or exceed thresholds for maturation may “residualize” in freshwater. Understanding life history diversity is important in steelhead hatchery programs. The objective of this investigation was to characterize life history diversity in Hood River, Oregon, hatchery winter‐run steelhead prior to release. We used both morphological and physiological indices to assess degree of smoltification in both sexes and maturation in males. Smoltification was categorized by measuring size, visual smolt index, and gill Na+/K+‐ATPase activity. All females were determined to be immature. Male reproductive development required histological staging of testes. Other indices of maturation—including gonadosomatic index, plasma 11‐ketotestosterone, and pituitary fshb and lhb and testis ifg3 and amh gene expression—were also employed, with varying degrees of success. Five phenotypes were described: (1) immature male and female parr; (2) precociously mature male parr; (3) male smolts in early to mid‐spermatogenesis that are likely to spawn after <1 year in the ocean; (4) males that might have attempted maturation, but failed; and (5) immature male and female smolts that could mature after >1 year in the ocean. Over three brood years, we estimated that 3–4% of the population could potentially residualize due to failure to smolt or precocious male maturation, 1–12% could mature after <1 year in the ocean (one salt male), and 84–95% could mature after >1 year in the ocean (two to three salt males and females). Based on previous studies conducted in the Hood River basin, the residualism rate estimated for this hatchery population is lower than that of naturally rearing Hood River steelhead.Received November 2, 2016; accepted February 14, 2017 Published online May 11, 2017

Marker assisted selection for spawning date and co-variation among economically important fitness traits in a commercial strain of rainbow trout (Oncorhynchus mykiss)

The effects of marker assisted selection for spawning date in males on embryonic developmental rate, growth related traits and precocious male maturation and phenotypic and genetic associations among traits were investigated in a commercial strain of rainbow trout (Oncorhynchus mykiss). The relationship between spawning date category of the sire (early or late) and developmental rate as measured by hatching time was inconsistent among families. However, two half-sib families produced by males with an allelic complement associated with late spawning date had higher rates of precocious male maturation and faster developmental rates than two families produced by males with earlier spawning date alleles. QTL analysis suggests that some of the co-variation between spawning date and developmental rate has a genetic basis as two QTL for developmental rate as measured by hatching time co-localized to the same markers known to be associated with spawning date in this strain. We observed no association between the spawning date category of the sire and progeny length at 61days post-fertilization (alevin stage), body weight at 381days (juveniles), body weight at 614days and specific growth rate, which suggests that selection for early or late spawning date alleles will have little effect on growth traits. Within families, faster developmental rates conferred a size advantage at 61days post-fertilization but not at 381 and 614days. Moreover, no correlation between developmental rate and the propensity of early male maturation was detected within families. Males that matured at 2years were significantly heavier at both 381 and 614days and had higher specific growth rates than immature males and females. Likewise, body weight at 614days and family were significant predictors for the propensity for early sexual maturation in males. This indicates that selection for greater body size will likely result in higher rates of unwanted precocious male maturation. Together, these results suggest that co-variation among economically important fitness traits may present potential trade-offs impacting selection goals. RelevanceAddresses feasibility of using molecular approaches in selective breeding programs.

Investigating the influence of nitrate nitrogen on post-smolt Atlantic salmon Salmo salar reproductive physiology in freshwater recirculation aquaculture systems

A major issue affecting land-based, closed containment Atlantic salmon Salmo salar growout production in water recirculation aquaculture systems (RAS) is precocious male maturation, which can negatively impact factors such as feed conversion, fillet yield, and product quality. Along with other water quality parameters, elevated nitrate nitrogen (NO3-N) has been shown to influence the reproductive development and endogenous sex steroid production in a number of aquatic animal species, including Atlantic salmon. We sought to determine whether elevated NO3-N in RAS can influence early maturation in post-smolt Atlantic salmon in an 8-month trial in replicated freshwater RAS. Post-smolt Atlantic salmon (102±1g) were stocked into six RAS, with three RAS randomly selected for dosing with high NO3-N (99±1mg/L) and three RAS set for low NO3-N (10±0mg/L). At 2-, 4-, 6-, and 8-months post-stocking, 5 fish were randomly sampled from each RAS, gonadosomatic index (GSI) data were collected, and plasma was sampled for 11-ketotestosterone (11-KT) quantification. At 4- and 8-months post-stocking, samples of culture tank and spring water (used as “makeup” or replacement water) were collected and tested for a suite of 42 hormonally active compounds using liquid chromatography/mass spectrometry, as well as for estrogenicity using the bioluminescent yeast estrogen screen (BLYES) reporter system. Finally, at 8-months post-stocking 8–9 salmon were sampled from each RAS for blood gas and chemistry analyses, and multiple organ tissues were sampled for histopathology evaluation. Overall, sexually mature males were highly prevalent in both NO3-N treatment groups by study’s end, and there did not appear to be an effect of NO3-N on male maturation prevalence based on grilse identification, GSI, and 11-KT results, indicating that other culture parameters likely instigated early maturation. No important differences were noted between treatment groups for whole blood gas and chemistry parameters, and no significant tissue changes were noted on histopathology. No hormones, hormone conjugates, or mycotoxins were detected in any water samples; phytoestrogens were generally detected at low levels but were unrelated to NO3-N treatment. Finally, low-level estrogenicity was detected in RAS water, but a NO3-N treatment effect could not be determined. The major findings of this study are i) the NO3-N treatments did not appear to be related to the observed male maturation, and ii) the majority of hormonally active compounds were not detectable in RAS water.

Stock Differences in Growth, Smolting, and Early Male Maturation in Hatchery Spring Chinook Salmon: a Common‐Garden Experiment

AbstractHatchery spring Chinook Salmon Oncorhynchus tshawytscha from Parkdale Hatchery on the Hood River, Oregon, and Carson National Fish Hatchery (CNFH) on the Wind River, Washington, were reared under a common‐garden experimental regime at CNFH over three consecutive brood years (2008–2010) to assess the effects of stock on smoltification and early male maturation. Rearing groups were monitored for size, percent solid (a surrogate for whole‐body lipid), gill Na+,K+‐ATPase activity, and rate of precocious maturation in males (i.e., age‐2 minijack rate). Despite rearing of the stocks under identical conditions, the out‐of‐basin Hood River stock was significantly smaller throughout the study and at release as smolts, had lower whole‐body lipid at release, and had lower gill Na+,K+‐ATPase activity at release than the Carson stock; furthermore, the Hood River stock exhibited much higher mean minijack rates than the Carson stock (45% versus 23% of males). Using logistic regression, we demonstrated that the threshold size for initiation of early male maturation was significantly lower for the Hood River stock than for the Carson stock, suggesting a genetic basis for this life history difference. The present study highlights the importance of understanding how specific genotypes may respond differently to the unique environmental conditions in a given hatchery environment. These differences may in turn influence physiological and life history pathways that affect smolt‐to‐adult return rates and the demography of returning adults.

Comparison of Growth-Related Traits and Gene Expression Profiles Between the Offspring of Neomale (XX) and Normal Male (XY) Rainbow Trout

All-female lines of fish are created by crossing sex reversed (XX genotype) males with normal females. All-female lines avoid the deleterious phenotypic effects that are typical of precocious maturation in males. To determine whether all-female and mixed sex populations of rainbow trout (Oncorhynchus mykiss) differ in performance, we compared the growth and gene expression profiles in progeny groups produced by crossing a XX male and a XY male to the same five females. Body weight and length were measured in the resulting all-female (XX) and mixed sex (XX/XY) offspring groups. Microarray experiments with liver and white muscle were used to determine if the gene expression profiles of large and small XX offspring differ from those in large and small XX/XY offspring. We detected no significant differences in body length and weight between offspring groups but XX offspring were significantly less variable in the value of these traits. A large number of upregulated genes were shared between the large XX and large XX/XY offspring; the small XX and small XX/XY offspring also shared similar expression profiles. No GO category differences were seen in the liver or between the large XX and large XX/XY offspring in the muscle. The greatest differences between the small XX and small XX/XY offspring were in the genes assigned to the "small molecule metabolic process" and "cellular metabolic process" GO level 3 categories. Similarly, genes within these categories as well as the category "macromolecule metabolic process" were more highly expressed in small compared to large XX fish.

The Effects of Variation in Rearing Conditions on Growth, Smolt Development, and Minijack Rate in Yearling Chinook Salmon: a Hatchery Scale Experiment

AbstractIn this investigation a single genetic stock of Hood River, Oregon, Chinook Salmon Oncorhynchus tshawytscha was reared at three different hatchery facilities over three brood years (2008–2010) and monitored for size, growth rate, gill Na+,K+‐ATPase activity, condition factor, whole body energetics, and precocious male maturation (age‐2 minijack rate). This experimental design provided a unique opportunity to isolate environmental from genetic effects on salmonid life history. Differences in the seasonal thermal regimes and associated growth profiles among the three facilities resulted in modest differences in smolt development but significant variation in size at release (range = 18 g body weight, 118 mm FL to 31 g body weight, 142 mm FL) and minijack rates (range = 4.8–57.1%) among groups. Previous studies have found a positive relationship between body size at release and minijack rates. However, in this investigation the release group with the largest mean body size consistently had the lowest minijack rates. This unique result may be due to the more natural thermal regime and feeding profile experienced by fish at this facility compared with that of the other two facilities and highlights the importance and potential benefits of adhering to a more “wildlike” growth profile in hatchery supplementation programs.Received February 24, 2014; accepted May 29, 2014

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.

Examining the Conflict between Smolting and Precocious Male Maturation in Spring (Stream‐Type) Chinook Salmon

AbstractPrecocious male maturation is a natural life history strategy for spring Chinook salmon Oncorhynchus tshawytscha. During spawning, precocious males employ a “sneaker” strategy to fertilize eggs in competition with full‐size anadromous adults. Hatchery rearing practices may increase the incidence of this phenotype beyond its natural levels. Previous research reported high rates (>40%) of precocious male maturation at age 2 (minijacks) in the Yakima River spring Chinook salmon supplementation program in Washington State. Minijack rates in wild populations are believed to be less than 5%. We compiled seasonal profiles for size, condition factor (K), gill Na+,K+‐ATPase activity, whole‐body lipid levels, plasma 11‐ketotestosterone (11‐KT), insulin‐like growth factor‐I (IGF‐I), and thyroxine (T4) in minijacks and immature smolts in the hatchery and during out‐migration. In the hatchery, minijacks were larger and had higher K, whole‐body lipid, plasma 11‐KT, and IGF‐I levels than smolts. Plasma T4 and gill Na+,K+‐ATPase activity increased in minijacks in spring, but the levels were slightly lower than those of smolts. Most minijacks are thought to remain resident in headwater streams throughout the summer in preparation for autumn spawning. A subset of these minijacks migrate hundreds of kilometers toward the ocean in the spring, only to reverse course later in the summer in an effort to return to their natal spawning grounds. These migrating minijacks had elevated plasma 11‐KT, IGF‐I, and T4 levels and gill Na+,K+‐ATPase activity. It is generally thought that smoltification and reproductive maturation are mutually exclusive life history events in salmonid fishes. This investigation examined the physiology of a unique phenotype in which smoltification and downstream migration appear to occur in fish that have already initiated the maturation process. These results suggest that hatchery programs with high minijack rates may produce significant numbers of fish that are maladapted for either smoltification or competing on the spawning grounds, and it is likely that they die in the freshwater environment before contributing to subsequent generations.

Sex-related changes in estrogen receptors and aromatase gene expression and enzymatic activity during early development and sex differentiation in the European sea bass ( Dicentrarchus labrax)

The present study addresses the role of aromatase and estrogen receptors in sex differentiation and development. With this purpose, a sea bass female- and a male-dominant group were obtained by successive size gradings since in this species females are already larger than males at the time of sex differentiation. Changes in cyp19a and cyp19b gene expression and enzymatic activity were monitored by a validated real-time PCR and a tritiated water assay, respectively, during early development and sex differentiation. Changes in mRNA expression of estrogen receptors, both erb1 and erb2, were also assessed during this period. Results show clear sex-related differences in cyp19a gene expression and enzymatic activity in gonads, with females exhibiting significantly higher levels than males at 150 days post hatching (DPH), when histological signs of sex differentiation were evident. cyp19b gene expression and activity in brain were detectable during early ontogenesis at 50 DPH but no clear sex-related differences were observed. Both erb1 and erb2 showed higher gene expression levels in testis than in ovaries around 200–250 DPH, corresponding with the time of testicular differentiation and precocious male maturation, but no sex-related differences were found in the brain. Together these results indicate that in the European sea bass high expression levels of cyp19a are associated with ovarian differentiation and thus cyp19a can be considered as a suitable molecular marker of ovarian differentiation. However, the involvement of cyp19b in sex differentiation cannot be concluded. In addition, the higher levels of erb1 and erb2 in males versus females during sex differentiation, coinciding with precocious male maturation in the sea bass, suggest an important role for these receptors in testicular development and maturation.

Growth Modulation Alters the Incidence of Early Male Maturation and Physiological Development of Hatchery‐Reared Spring Chinook Salmon: A Comparison with Wild Fish

AbstractPrevious studies conducted at the Cle Elum Spring Chinook Salmon Supplementation Hatchery in Washington State demonstrated that 37–49% of the male Chinook salmon Oncorhynchus tshawytscha released from this facility in its first years of operation precociously matured at age 2 rather than the more typical age 4. We examined the effects of altering seasonal growth rate on the incidence of age‐2 male maturation in an experimental subset of that population and compared their physiological development (size, growth rate, condition factor, whole‐body lipid, gill Na+,K+‐ATPase activity, and plasma insulin‐like growth factor‐I [IGF‐I]) with that of both hatchery (production) and wild fish. Altering summer and autumn rations resulted in four growth trajectories with the following size and precocious male maturation rates: The high summer—high autumn growth trajectory produced fish averaging 25 g and 69% precocious maturation; the high summer—low autumn trajectory yielded fish that averaged 18 g and exhibited 58% precocious maturation; the low summer—high autumn trajectory produced 18‐g fish with 51% precocious maturation; and the low summer—low autumn trajectory yielded fish averaging 16 g and 42% precocious maturation. Production fish averaged 22 g and exhibited a 53% precocious maturation rate. The high summer growth treatments and production fish were largest among all groups and had higher plasma IGF‐I, adiposity levels, and precocious male maturation rates than did the low summer growth treatments. Wild fish were significantly smaller and leaner and had much lower plasma IGF‐I levels than all other groups. Gill Na+,K+‐ATPase activity was not different between groups, suggesting that there was no differential effect on smoltification. Growth modulation reduced the precocious male maturation rate by 39% among experimental treatments and by 21% between production fish and the low—low treatment. However, the maturation rate and adiposity of hatchery fish differed markedly from those of wild fish, suggesting that more dramatic alterations of rearing regime may be required to further reduce the prevalence of this phenotype in cultured fish.