Search

We evaluated how genotype (stock source, parental line, chromosomal sex) and temperature interact to influence gonad development and phenotypic sex of Oncorhynchus mykiss. Embryos were generated from single pair matings of natural-origin and first-generation hatchery-origin O. mykiss held at ambient or elevated (5 °C above ambient) water temperature. Exposure to elevated temperature lasted from fertilization until the onset of exogenous feeding, after which all experimental groups were maintained at ambient temperature. Sexual phenotype was determined by histology and sexual genotype by the OmyY1 marker. There was 99% concordance among fish sexed both phenotypically and genotypically, demonstrating that experimental factors, including elevated rearing temperatures, did not result in sex change. Approximately 10% of the histologically examined fish showed no evidence of gonad development beyond the indifferent stage. Most of these fish were from hatchery family lines.

Chinook salmon (Oncorhynchus tshawytscha) are widely distributed across the globe, with native stocks in the North Pacific Ocean and self-sustained populations in both the Northern and Southern hemispheres. In their native range, Chinook salmon face many conservation and management challenges, including depleted stocks, loss of genetic diversity, and hatchery influences, whereas naturalized range expansion poses a threat to novel ecosystems. Therefore, ways to improve stock discrimination would be a useful tool for fishery managers. Here, we evaluated otolith shape variation in Chinook salmon as a potential tool for stock discrimination using wavelet coefficients and Fourier harmonics in three case studies at multiple spatial scales. We adopted a simple Classification Tree model that used otolith shape variation to separate Chinook salmon groups. We found best performance of the model occurring between hemispheres, followed by Oregon basins, within-watershed Elk River, Oregon, and lastly among South American basins. Otolith shape analysis is a promising tool for stock discrimination if used in conjunction with other methods to better understand plasticity of anadromous species that use pan-environmental systems.

Salmon straying is often defined as the failure of adults to return to their natal river system. However, straying within a river basin can be problematic if hatchery salmon do not return to their hatchery of origin and subsequently spawn in the wild with natural-origin salmon. We examined within-river straying patterns from 34 years of coded-wire tag data, representing 29 941 hatchery fall Chinook salmon (Oncorhynchus tshawytscha) in the Elk River, Oregon, USA. Using classification tree analysis, we found that females and larger salmon were more likely to be recovered on the spawning grounds than males and smaller fish. Females larger than 980 mm had a 51.6% likelihood of recovery on the spawning grounds rather than at the Elk River Hatchery. Our findings raise questions about the behavior of straying adults and implications for management of these stocks, with a focus on methods to reduce within-river straying. We recommend further studies to determine whether carcass recoveries are fully representative of hatchery salmon that stray within the Elk River basin.

Fluctuating asymmetry is the non-directional deviations from bilateral symmetry and occurs across organisms. Fish otoliths are often used to test for differences in symmetry as otoliths aid in hearing, homing, and balance. Here, we evaluated the symmetry of otolith pairs in adult Chinook Salmon between wild and hatchery-origin stocks. Pacific salmon are economically and ecologically important to the Pacific Northwest, USA. Chinook Salmon are widely distributed throughout the North Pacific Ocean, yet several wild populations are federally listed as endangered or threatened due to depleted stocks, loss of genetic diversity, and hatchery contribution to wild stocks. As such, fishery managers are concerned with the health and condition of hatchery-origin fish and their impacts on wild populations. We included both hatchery and wild-origin Chinook Salmon from the Coast Mountain and Willamette regions in Oregon as well as hatchery populations from southeast Alaska. We evaluated several metrics to test shape variation and symmetry between the left and right sagittal otoliths. We found consistently more asymmetry in otoliths from hatchery origin than wild Chinook Salmon within seven out of eight total metrics. These results could have conservation and management implications as hatchery-origin Chinook Salmon can reduce pressure from wild stocks while continuing to support commercial and recreational industries.

There is a growing demand within research and conservation hatcheries to rear fish that more closely approximate the smaller size and leaner body composition of their wild counterparts. Low-lipid diets may help achieve this goal as they can provide all the nutritional needs of young fish and can lead to slower growth and leaner bodies. We compared growth of Chinook Salmon Oncorhynchus tshawytscha fed three experimental low-lipid diets (11–12, 8–9, 4–6% lipid) at the onset of feeding with a commercially available high-lipid diet (18–20%) and an experimentally formulated high-lipid control (13.9% lipid). After 5 mo on their respective treatments, the size, growth rate, and daily growth index of fish on the commercial diet were significantly higher than those on the three low-lipid diets. We also compared whole-body lipid content across our five diet treatments. Whole-body lipid content was significantly different across the five diets, with fish fed the commercial diet having, on average, an almost twofold higher lipid content over fish fed the lowest lipid diet formulation. We present comparable data from a limited sample of wild juvenile conspecifics as observations. We suggest that low-lipid starter diets can be used to produce healthy fish that more likely emulate some of the variations in size and body composition of wild fish.

We tested the prediction that a complex physical rearing environment would enhance short-term spatial memory as assessed by learning ability in a spatial navigation task in juvenile Chinook salmon Oncorhynchus tshawytscha. We reared fish in two low-density treatments, where fish were either in bare fiberglass tanks (bare) or in tanks with physical structure (complex). We also tested conventionally reared high-density hatchery fish to compare with these other experimental treatments. Our reason for including this third hatchery treatment is that the two low-density treatments, aside from the manipulation of structure, followed a rearing programme that is designed to produce fish with more wild-like characteristics. We tested individually marked fish for seven consecutive days and recorded movement and time to exit a testing maze. Stimulus conspecific fish outside the exit of the maze provided positive reinforcement for test fish. Fish from the bare treatment were less likely to exit the start box compared with fish in the complex and hatchery treatments. However, fish in the hatchery treatment were significantly more likely to exit the maze on their own compared with both the bare and complex treatments. Hatchery fish effectively learned the task as shown by a decrease in the number of mistakes over time, but the number of mistakes was significantly greater on the first day of trials. Increasing habitat complexity with structure may not necessarily promote spatial learning ability, but differences between hatchery and experimental treatments in rearing density and motivation to be near conspecifics likely led to observed behavioural differences.

Understanding how rearing environments influence the stress response is relevant to many fish management practices. This is particularly relevant in aquaculture, where it is important to be able to minimize the effects of stress to enhance animal wellbeing. The stress response is also interesting from a basic science perspective, where it is important to understand how environmental differences can influence phenotypic traits and the physiological reaction to stressors. We tested the hypothesis that rearing fish in a more complex environment would reduce their stress response when presented with stressors. Specifically, we tested for the effect of structure in rearing tanks on the stress response of juvenile Chinook Salmon (Oncorhynchus tshawytscha) exposed to a handling and crowding stressor, something like hatchery fish might experience during transportation to new locations. For both rearing treatments (with and without structure), we compared fish that were subjected to the stressor to fish sampled from the respective rearing tank as the control. For the stressed treatment, we subjected fish to net capture followed by three hours in lowered water levels in a novel tank and then moved to a second novel holding tank. This process was designed to mimic typical stressors fish may experience at a hatchery. We analyzed plasma collected before the start of the stressor, during the stressor, and throughout 20 h post-stressor for cortisol in both stressed and unstressed fish. For both rearing treatments, fish that experienced the stressor had elevated plasma cortisol compared to control fish. However, the cortisol levels of fish in the stressed treatment reared with structure were significantly less than fish reared without structure. Additionally, plasma cortisol levels in structure-reared fish returned to baseline by 20 h post-stress while fish reared without structure had not fully recovered. Our findings suggest that increasing complexity of the rearing environment might be advantageous as a way of minimizing effects of handling-type stressors.

The number of subsea cables in the marine environment is likely to grow substantially in the near future. Arrays of energy‐generating windmills or wave power generators are planned for installation in the coastal waters of many countries worldwide. The electricity generated by these and other marine energy sources will be transported to shore through cables with the current and voltage creating electromagnetic fields (EMFs). Furthermore, there are also plans for the installation of undersea cables to interconnect countries and islands for the purpose of sharing power and communications. These also will generate EMFs in the marine environment. While shielding can negate the presence of direct electric fields, induced electric and magnetic fields readily penetrate into the water column. Cables carrying electric current produce anomalies in the earth's main field, which could have the potential for disrupting the migrations of fishes and diverse marine animals that rely on magnetic cues for orientation or navigation. Studies designed to test how these anthropogenic magnetic fields disrupt magnetic orientation have only recently started to be conducted. Given the cultural, economic, and conservation value of many of the species potentially at risk, such work should be immediately prioritized.

Accurate and precise terminology is critical for clarity and information transfer. Lake charr Salvelinus namaycush developmental terminology is often incorrectly and inconsistently applied and consists of terms borrowed from other salmonids. Terms currently used may not identify developmental stages, are not synonymous with formal terminology, and are not ecologically relevant. We propose a standard lake charr-specific terminology consisting of: (1) egg: a haploid, unfertilized gamete; (2) pre-hatch embryo: a developing embryo within a chorion; (3) free embryo: post-hatch embryo, used until absorption of the external yolk sac; (4) post-embryo: lake charr with internal or fully absorbed yolk sac, usually with parr marks and inflated gas bladder, and still resident on a spawning area; (5) age-0: lake charr during the period between leaving spawning grounds and December 31 of the first year of life; (6) juvenile: interval between the end of age-0 (January 1) and the onset of maturity; (7) adult: life stage after reproductive maturity; and (8) senescent: stage after growth and reproductive capacity cease. The recommended terminology is specific to lake charr and strikes a balance between accurate life-stage specific terms that reflect development, and the practicality of life-stage terms that can be assigned by field biologists and fishery managers.

The Cichlidae, one of the most diverse families of vertebrates, is the subject of the volume entitled “The Behavior, Ecology and Evolution of Cichlid Fishes” which we introduce here. Cichlids are major members of their communities. They are socioeconomically important in fisheries, aquaculture, and the ornamental trade. The immense number of cichlid diverse forms challenge researchers to integrate new tools to delineate species, construct phylogenies, and determine species diversity; and their detailed study has significantly contributed to evolution models. Cichlid researchers have a strong tradition of taking a comparative approach. This book reflects that tradition with 20 reviews written by internationally recognized experts providing an integrative sub-disciplinary perspective, often including molecular studies. This volume is broad in scope, beginning with a review of the history of cichlid studies over two centuries. Next, four reviews examine cichlid diversification at different scales in African and Neotropical lakes and rivers; followed by four on conservation and management including species delimitation tools. The midsection, covering cichlid behavioral adaptations and their underlying mechanisms and effects, concerns the senses, parental care, sociality, and neurobiology. The last part of the book includes reviews on cichlid ecology, plasticity and evo-devo and closes with an examination of cichlids as models for biomedicine.

This volume represents the first synthesis of the biology, ecology, distribution, and management of the lake charr Salvelinus namaycush (commonly known as lake trout in North America) in more than 40 years. An updated distribution for the species precedes complete syntheses of the paleoecology, ecological and genetic diversity, habitat, movement and behavior, life history and population dynamics, trophic and reproductive ecology, contaminants and ecotoxicology, and management. Finally, a standardized terminology for lake charr early life history is presented in an attempt to correct historical inaccuracies. Our intent is that this volume will serve the next half-century of biologists, ecologists, and fishery managers as the reference for the species—a great icon of the glaciated regions of North America.

Mate choice in most organisms is not random, but determined by a suite of interacting traits and environmental factors. While the selective pressures underlying differences in mate choice between species, populations, individuals and even within individuals has been gaining interest, there still remains unexplained variation in mate preferences especially in non-model systems. Despite being of social, environmental and economic importance there is comparatively little known about how salmonids and other tetraploids make mate choice decisions in the wild and the resultant reproductive success (i.e. the number of offspring which survive to sexual maturity). Resolving questions related to salmonid mate choice is of particular importance given that humans have been supplementing salmon populations through aquaculture for decades. Despite these efforts, hatchery produced fish have lower reproductive success relative to their wild counterparts and salmon populations are declining. Most studies on mate choice and reproductive success in salmonids focus on body size and major histocompatibility complex based choice. However, mate choice can also be affected by other factors including other genetic factors, predation risk and social environment. Here, we (a) synthesize what is presently known about mate choice and reproductive success in salmonids, (b) identify gaps in knowledge and areas where there is a lack of consensus in results, and (c) suggest interdisciplinary ways of advancing our understanding of mate choice in salmonids and other polyploids.

The effects of egg size on early development and growth of steelhead Oncorhynchus mykiss were recorded for more than 200 days following hatching. Fish from smaller eggs hatched sooner and at a smaller size than fish from larger eggs, but fish from smaller eggs showed consistently higher growth rates than fish from larger eggs. Since many life-history attributes appear to be determined by size or growth rate at age during the first year, egg size could be a significant predictor of important changes in the life history of individuals.

Life history variation is fundamental to the evolution of Pacific salmon and their persistence under variable conditions. We discovered that Chinook salmon sort themselves into surface- and bottom-oriented groups in tanks within days after exogenous feeding. We hypothesised that this behaviour is correlated with subsequent differences in body morphology and growth (as measured by final length and mass) observed later in life. We found consistent morphological differences between surface and bottom phenotypes. Furthermore, we found that surface and bottom orientation within each group is maintained for at least one year after the phenotypes were separated. These surface and bottom phenotypes are expressed across genetic stocks, brood years, and laboratories and we show that the proportion of surface- and bottom-oriented offspring also differed among families. Importantly, feed delivery location did not affect morphology or growth, and the surface fish were longer than bottom fish at the end of the rearing experiment. The body shape of the former correlates with wild individuals that rear in mainstem habitats and migrate in the fall as subyearlings and the latter resemble those that remain in the upper tributaries and migrate as yearling spring migrants. Our findings suggest that early self-sorting behaviour may have a genetic basis and be correlated with other phenotypic traits that are important indicators for juvenile migration timing.

Intraspecific phenotypic diversity is the raw material for evolution, so understanding its origin and maintenance is critically important for conservation of biodiversity. Intraspecific diversity in a trait or a suite of traits can result from genetic diversity and/or phenotypic plasticity. The two are, however, not independent as plasticity has been shown to evolve. In this study, we evaluated the importance of phenotypic plasticity in generating morphological diversity in populations of small benthic Arctic charr in Iceland, using a rearing experiment with contrasting modes of feeding. We also examined the association between phenotypic plasticity in offspring groups generated by the contrasting feeding modes and important ecological variables characterising the natural habitats of the respective populations. Although the level of plasticity could not be related to any of the ecological measurements, clear differences in morphological reaction norms among populations suggest that plasticity is an important aspect of morphological diversity of the charr. It is not clear whether that plasticity is adaptive, but it is notable that reaction norms in all populations have similar reaction to the treatments.

Seasonal timing of transportation and acclimation of juvenile Chinook salmon (Oncorhynchus tshawytscha) between hatcheries may affect osmoregulation and survival. We investigated the duration of ti...

The Pacific Lamprey Entosphenus tridentatus, an anadromous fish native to the northern Pacific Ocean and bordering freshwater habitats, has recently experienced steep declines in abundance and range contractions along the West Coast of North America. During the early 1990s, Native American tribes recognized the declining numbers of lamprey and championed their importance. In 2012, 26 entities signed a conservation agreement to coordinate and implement restoration and research for Pacific Lamprey. Regional plans have identified numerous threats, monitoring needs, and strategies to conserve and restore Pacific Lamprey during their freshwater life stages. Prime among these are needs to improve lamprey passage, restore freshwater habitats, educate stakeholders, and implement lamprey-specific research and management protocols. Key unknowns include range-wide trends in status, population dynamics, population delineation, limiting factors, and marine influences. We synthesize these key unknowns, with a focus on ...

A variety of animals sense Earth's magnetic field and use it to guide movements over a wide range of spatial scales. Little is known, however, about the mechanisms that underlie magnetic field detection. Among teleost fish, growing evidence suggests that crystals of the mineral magnetite provide the physical basis of the magnetic sense. In this study, juvenile Chinook salmon (Oncorhynchus tshawytscha) were exposed to a brief but strong magnetic pulse capable of altering the magnetic dipole moment of biogenic magnetite. Orientation behaviour of pulsed fish and untreated control fish was then compared in a magnetic coil system under two conditions: (1) the local magnetic field; and (2) a magnetic field that exists near the southern boundary of the natural oceanic range of Chinook salmon. In the local field, no significant difference existed between the orientation of the control and pulsed groups. By contrast, orientation of the two groups was significantly different in the magnetic field from the distant site. These results demonstrate that a magnetic pulse can alter the magnetic orientation behaviour of a fish and are consistent with the hypothesis that salmon have magnetite-based magnetoreception.

In September 2013, hatchery reared sub-yearling steelhead trout, Oncorhynchus mykiss, juveniles were separated into three groups and were reared in 3 different water temperature regimes (ambient (14.4–16.9 °C), cool (10.6–11.8 °C), and warm (20.0–22.3 °C)) in circular hatchery tanks for approximately 1.5 weeks. In Experiment 1, an individual steelhead trout juvenile acclimated in ambient water was transferred into a two-choice stream tank where the fish received either ambient (n = 12) or cool (n = 6)/warm (n = 6) water. During a 30 min observation, steelhead trout juveniles clearly avoided both cool and warm water areas. In Experiment 2, we transferred an individual steelhead trout juvenile, which was acclimated in cooled water, into the cool two-choice stream tank and introduced ambient water (relative water temperature increase) (n = 6). Such an increase caused the juvenile to stay in cool water, suggesting that once steelhead juvenile have acclimated in cool water for 1.5 weeks, these fish would avoid relatively higher temperature (ambient) water and stay in a cooler area. In Experiment 3, we transferred an individual steelhead trout juvenile, which was acclimated in warmed water, into the warm two-choice stream tank and introduced ambient water (relative water temperature decrease) (n = 6). As a result, the relative decrease in water temperature did not influence swimming location choice of the juveniles, suggesting that juvenile steelhead trout do not avoid ambient water (relatively cooler water) even after they were acclimated in warm water. Based on these findings, we suggest that water temperature changes may promote swimming location choice in steelhead trout juveniles, depending on the changing patterns.

Long-distance migrants, including Pacific salmon (Oncorhynchus spp), can use geomagnetic information to navigate. We tested the hypothesis that a "magnetic map" (i.e., an ability to extract positional information from Earth's magnetic field) also exists in a population of salmon that do not undertake oceanic migrations. This study examined juvenile Atlantic salmon (Salmo salar) originally from a nonanadromous population in Maine transferred ∼60 years ago to a lake in central Oregon. We exposed juveniles to magnetic displacements representative of locations at the latitudinal boundaries of the Pacific salmon oceanic range in the North Pacific and at the periphery of their ancestral oceanic range in the North Atlantic. Orientation differed among the magnetic treatments, indicating that Atlantic salmon detect map information from the geomagnetic field. Despite no recent history of ocean migration, these fish displayed adaptive orientation responses similar to those observed in native Pacific salmonids. These findings indicate that use of map information from the geomagnetic field is a shared ancestral character in the family Salmonidae and is not restricted to populations with anadromous life histories. Lastly, given that Atlantic salmon are transported throughout the world for capture fisheries and aquaculture, such a robust navigational system is of some concern. Escaped individuals may have greater potential to successfully navigate, and thus invade, introduced habitats than previously suspected.

Studies on hydromineral balance in fishes frequently employ measurements of electrolytes following euthanasia. We tested the effects of fresh- or salt-water euthanasia baths of tricaine mesylate (MS-222) on plasma magnesium (Mg(2+)) and sodium (Na(+)) ions, cortisol and osmolality in fish exposed to saltwater challenges, and the ion and steroid hormone fluctuations over time following euthanasia in juvenile spring Chinook salmon (Oncorhynchus tshawytscha). Salinity of the euthanasia bath affected plasma Mg(2+) and Na(+) concentrations as well as osmolality, with higher concentrations in fish euthanized in saltwater. Time spent in the bath positively affected plasma Mg(2+) and osmolality, negatively affected cortisol, and had no effect on Na(+) concentrations. The difference of temporal trends in plasma Mg(2+) and Na(+) suggests that Mg(2+) may be more sensitive to physiological changes and responds more rapidly than Na(+). When electrolytes and cortisol are measured as endpoints after euthanasia, care needs to be taken relative to time after death and the salinity of the euthanasia bath.

What is the nature of evolutionary divergence of the jaw skeleton within the genus Oncorhynchus? How can two associated bones evolve new shapes and still maintain functional integration? Here, we introduce and test a "concordance" hypothesis, in which an extraordinary matching of the evolutionary shape changes of the dentary and angular articular serves to preserve their fitting together. To test this hypothesis, we examined morphologies of the dentary and angular articular at parr (juvenile) stage, and at three levels of biological organization—between salmon and trout, between sister species within both salmon and trout, and among three types differing in life histories within one species, Oncorhynchus mykiss. The comparisons show bone shape divergences among the groups at each level; morphological divergence between salmon and trout is marked even at this relatively early life history stage. We observed substantial matching between the two mandibular bones in both pattern and amount of shape variation, and in shape covariation across species. These findings strongly support the concordance hypothesis, and reflect functional and/or developmental constraint on morphological evolution. We present evidence for developmental modularity within both bones. The locations of module boundaries were predicted from the patterns of evolutionary divergences, and for the dentary, at least, would appear to facilitate its functional association with the angular articular. The modularity results suggest that development has biased the course of evolution.

In salmonids with partial migration, females are more likely than males to undergo smoltification and migrate to the ocean (vs. maturing in freshwater). However, it is not known whether sex affects survivorship during smolt migration (from fresh water to entry into the ocean). We captured wild steelhead (Oncorhynchus mykiss) smolts in two coastal Oregon rivers (USA) and collected fin tissue samples for genetic sex determination (2009; N = 70 in the Alsea and N = 69 in the Nehalem, 2010; N = 25 in the Alsea). We implanted acoustic tags and monitored downstream migration and survival until entry in to the Pacific Ocean. Survival was defined as detection at an estuary/ocean transition array. We found no effect of sex on smolt survivorship in the Nehalem River in 2009, or in the Alsea River in 2010. However, males exhibited significantly lower survival than females in the Alsea River during 2009. Residency did not influence this result as an equal proportion of males and females did not reach the estuary entrance (11% of males, 9% of females). The sexes did not differ in timing or duration of migration, so those variables seem unlikely to explain sex-biased survivorship. Larger males had higher odds of survival than smaller males in 2009, but the body size of females did not affect survivorship. The difference in survivorship between years in the Alsea River could be due to flow conditions, which were higher in 2010 than in 2009. Our findings suggest that sex may affect steelhead smolt survival during migration, but that the difference in survivorship may be weak and not a strong factor influencing adult sex ratios.

Piscivory by birds can be significant, particularly on fish in small streams and during seasonal low flow when available cover from predators can be limited. Yet, how varying amounts of cover may change the extent of predation mortality from avian predators on fish is not clear. We evaluated size-selective survival of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in replicated semi-natural stream sections. These sections provided high (0.01 m2 of cover per m2 of stream) or low (0.002 m2 of cover per m2 of stream) levels of instream cover available to trout and were closed to emigration. Each fish was individually tagged, allowing us to track retention of individuals during the course of the 36-day experiment, which we attributed to survival from predators, because fish had no other way to leave the streams. Although other avian predators may have been active in our system and not detected, the only predator observed was the belted kingfisher Megaceryle alcyon, which is known to prey heavily on fish. In both treatments, trout >20.4 cm were not preyed upon indicating an increased ability to prey upon on smaller individuals. Increased availability of cover improved survival of trout by 12% in high relative to low cover stream sections. Trout also survived better in stream sections with greater shade, a factor we could not control in our system. Collectively, these findings indicate that instream cover and shade from avian predators can play an important role in driving survival of fish in small streams or during periods of low flow.

Straying by hatchery-reared salmon is a major concern for conservation and recovery of many salmon populations. Fisheries managers have attempted to minimize negative ecological and genetic interactions between hatchery and wild fish by using parr-smolt acclimation facilities to ensure successful olfactory imprinting and homing fidelity. However, the effectiveness of offsite acclimation for returning adults to targeted locations has been mixed. Since laboratory and field studies indicate that the period of hatching and emergence from the natal gravel is a sensitive period for olfactory imprinting, we propose an alternative imprinting approach wherein salmon are exposed as embryos to targeted waters transferred to their rearing hatchery. To test the feasibility of this approach, we conducted a series of electrophysiological and behavioral experiments to determine whether water can be successfully transferred, stored, and treated for pathogens without jeopardizing its chemical integrity. Stream water could ...

Organisms use a variety of environmental cues to orient their movements in three-dimensional space. Here, we show that the upward movement of young Chinook salmon ( Oncorhynchus tshawytscha ) emerging from gravel nests is influenced by the geomagnetic field. Fish in the ambient geomagnetic field travelled farther upwards through substrate than did fish tested in a field with the vertical component inverted. This suggests that the magnetic field is one of several factors that influences emergence from the gravel, possibly by serving as an orientation cue that helps fish determine which way is up. Moreover, our work indicates that the Oncorhynchus species are sensitive to the magnetic field throughout their life cycles, and that it guides their movements across a range of spatial scales and habitats.

The relative movement of juvenile steelhead Oncorhynchus mykiss reared on two treatments was investigated to provide insight on the effect of structure in the rearing environment on the behaviour of the fish before potential release into a natural river system. The progeny of wild broodstock were reared either in the presence or absence of structure in the tank environment for 7 months at the Oregon Hatchery Research Center located in Oregon, U.S.A. Behavioural assessments, including movement response to a simulated predator, showed that fish reared on structure moved a similar amount (based on line crosses) as fish reared in bare hatchery tanks. No significant difference was observed in the proportion of time spent near a small structure within the behavioural test tank between the two treatments, but all fish showed decreased movement over time with each subsequent predation event. Fish from both treatments spent 30% of their time in the section of the tank containing the structure, which was one section out of a total of eight sections. In both treatments, fish foraged 20% of the time in the 2 min following the introduction of live tubifex prey (two separate events). Overall, similar movement and foraging responses occurred following mock predation events for juveniles reared either with or without structure. Developing assessment tools such as these, that measures behaviours related to survival based on rearing environment should allow managers to better predict the survival and effect of rearing conditions on the release of hatchery-origin fish into the wild.

Body morphology of juvenile Chinook salmon Oncorhynchus tshawytscha in the upper Willamette River, Oregon, U.S.A., was analysed to determine if variation in body shape is correlated with migratory life-history tactics followed by juveniles. Body shape was compared between migrating juveniles that expressed different life-history tactics, i.e. autumn migrants and yearling smolts, and among parr sampled at three sites along a longitudinal river gradient. In the upper Willamette River, the expression of life-history tactics is associated with where juveniles rear in the basin with fish rearing in downstream locations generally completing ocean ward migrations earlier in life than fish rearing in upstream locations. The morphological differences that were apparent between autumn migrants and yearling smolts were similar to differences between parr rearing in downstream and upstream reaches, indicating that body morphology is correlated with life-history tactics. Autumn migrants and parr from downstream sampling sites had deeper bodies, shorter heads and deeper caudal peduncles compared with yearling smolts and parr from the upstream sampling site. This study did not distinguish between genetic and environmental effects on morphology; however, the results suggest that downstream movement of juveniles soon after emergence is associated with differentiation in morphology and with the expression of life-history variation.

Induced triploidy typically causes sterility in teleost fishes, and has therefore been proposed as a tool to manage genetic risks that farmed and hatchery-produced salmon pose to wild populations. Application of this technology for aquaculture has been challenged by inferior growth, survivorship and, in the case of free-ranging anadromous salmonids, relatively low numbers of adult returns. There is little information on whether or not triploidy affects the physiological development of juvenile salmonids in ways that impair their ability to grow, imprint on natal waters, survive, and return from the ocean as adults. In this study we pressure treated fertilized eggs to produce two cohorts of triploid hatchery steelhead trout (i.e., anadromous Oncorhynchus mykiss). We calculated survivorship through early life stages, and measured gill ATPase and plasma thyroxine (T4) for yearling triploids and their full-sibling diploid controls. We found no clear pattern of difference between diploid and triploid steelhead for the biomarkers of smoltification T4 or ATPase. After a year of freshwater rearing, we transferred 448 tagged treatment and control fish to a saltwater tank, and tracked their growth and survivorship for over 15 months. Diploids outperformed triploids in growth and, by the end of our study, survivorship of diploids (72%) was more than twice that of triploids (35%). Our findings suggest that inferior growth and survivorship of triploids in saltwater seriously challenge the application of this technology for free-ranging steelhead and, by extension, Pacific salmon. Additional research is needed to identify and offset the causal mechanisms underpinning triploid attrition during saltwater rearing.

The endemic cyprinid species flock of Lake Lanao, Philippines is a classic example of explosive evolution. Based on historical surveys, most of the 18 endemic cyprinid species in Lake Lanao are now believed to be extinct. We compared results of landing and market surveys conducted in 2008 to information from historical surveys. Field sampling and fishermen interviews provided additional information on the status of the endemic and other fish species in Lake Lanao. Puntius lindog and Puntius tumba were the only two endemic species recorded in 2008, accounting for 0.01 % and 0.04 % respectively of the total weight harvested. Our discovery that at least two endemic cyprinids remain in Lake Lanao is surprising and significant as the lake is increasingly imperiled by human disturbances, exploitation and introduced species. Protecting and conserving the remaining endemic species are important management priorities.

The Pacific salmonid species Oncorhynchus mykiss is separated into a migratory form (steelhead trout) and a non-migratory form (rainbow trout). A decrease in water temperature is likely a cue triggering downstream behavior in the migratory form, and testosterone inhibits onset of this behavior. To elucidate differences in sensitivity to water temperature decreases between the migratory and non-migratory forms and effect of testosterone on the sensitivity, we examined two experiments. In experiment 1, we compared changes in body temperature during a short-term decrease in water temperature between both live and dead steelhead and rainbow trout. In experiment 2, we investigated effects of testosterone on body temperature decrease in steelhead trout. Water temperature was decreased by 3°C in 30min. The body temperature of the steelhead decreased faster than that of the rainbow trout. In contrast, there was no significant difference in the decrease in body temperature between dead steelhead and rainbow trout specimens. The body temperature of the testosterone-treated steelhead trout decreased more slowly than that of control fish. Our results suggest that the migratory form is more sensitive to decreases in water temperature than the non-migratory form. Moreover, testosterone might play an inhibitory role in sensitivity to such decreases.

Our series of manuscripts on Threatened Fishes of the World came to an end after a prolonged and increasingly depressing and frustrating history. Prolonged because the series extended from 1995 to 2013, much longer than was anticipated. Increasingly depressing because it became clear to even the most skeptical reader that the status of a great many fishes is a matter of real concern. Frustrating because the accounts mostly presented the same picture for almost every species. The species accounts range from the largest fish species, the whale shark (Rhincodon typus) to one of the smallest (Tanichthys albonubes), in freshwater, marine and brackish water systems (Table 1). The list includes some species that almost certainly are extinct, such as the Yangtze paddlefish (Xiphurus gladius), and some that are relatively abundant and widespread, such as the North American lake sturgeon (Acipenser fulvescens). Some species have global distributions, other are restricted to a single desert spring (Cyprinodon diabolis). Several cautions are obvious for this species list. Since contributions were unsolicited, and judged on their individual merits, it is not possible to analyze or interpret these reports as any objective measure of the number or distribution of threatened fish species. That was never the intention of this series. Other publications (Helfman 2007) are definitive efforts that were designed to address those important questions (Albins et al. 2013). Similarly, it is not possible to draw any conclusions from our series on Threatened Fishes as to the geographic, phylogenetic or systematic distribution of species. In fact, some papers must be regarded as doubtful reports of threatened species, since they probably represent only local color variants of broadly distributed species that cannot be considered as threatened (e.g., the aurora form of Salvelinus fontinalis, Salmo trutta caspias). We still receive a few manuscript submission each year, although the journal website clearly states that we are no longer accepting manuscripts for the series. It proved to be increasingly difficult to judge the claimed threatened status for taxonomic units reported from areas with very limited information on species distributions and abundance. Helfman (2013) has done an admirable job to demonstrate the profound differences and difficulties that exist among different countries and jurisdictions where there is reasonable confidence for species identification and knowledge of population status. It is a simple exercise for any undergraduate ichthyology class in almost any place on earth to demonstrate that we have very limited information on the biology, ecology and population status of most local fish species (Scott and Crossman 1973). I organized an invited session on Threatened Fishes for the annual meeting of the AAAS in Chicago in February 2011. Several papers from that session are Environ Biol Fish (2013) 96:1135–1149 DOI 10.1007/s10641-013-0174-y

SummaryIn the final phase of their spawning migration, Pacific salmon use chemical cues to identify their home river, but how they navigate from the open ocean to the correct coastal area has remained enigmatic [1]. To test the hypothesis that salmon imprint on the magnetic field that exists where they first enter the sea and later seek the same field upon return [2–4], we analyzed a 56-year fisheries data set on Fraser River sockeye salmon, which must detour around Vancouver Island to approach the river through either a northern or southern passageway [5, 6]. We found that the proportion of salmon using each route was predicted by geomagnetic field drift: the more the field at a passage entrance diverged from the field at the river mouth, the fewer fish used the passage. We also found that more fish used the northern passage in years with warmer sea surface temperature (presumably because fish were constrained to more northern latitudes). Field drift accounted for 16% of the variation in migratory route used, temperature 22%, and the interaction between these variables 28%. These results provide the first empirical evidence of geomagnetic imprinting in any species and imply that forecasting salmon movements is possible using geomagnetic models.

Anadromous salmonids are viewed as a prized commodity and cultural symbol throughout the Pacific coast of North America. Unfortunately, several native salmonid populations are threatened or at risk of extinction. Despite this, little is known about the behavior and survival of these fish as the juveniles transition from freshwater to the ocean. Our primary objectives were to estimate survival of juvenile steelhead migrating between trapping sites and the ocean and evaluate whether survival in the estuary varies temporally (within a year) or spatially (within and between estuaries) within the same distinct population segment. We also evaluated whether flow or fork length were correlated with survival and collected information on variables that have been demonstrated to affect smolt survival in other studies to lend insight regarding differences in survival estimates between basins. We compared run timing, migration rate, survival, condition factor, age composition and time of residence in the estuary for steelhead outmigrants from each basin and measured parasite loads in outmigrating steelhead to evaluate potential differences in parasite density and parasite community between basins. In 2009, we implanted acoustic transmitters in 139 wild steelhead smolts in two small rivers on the Oregon Coast. In general, only 40–50 % of the wild steelhead smolts tagged at upstream smolt traps were detected entering the ocean. The majority of mortality occurred in the lower estuary near the ocean. Wild steelhead smolts typically spent less than 1 day in the estuary in both basins. Using similar data from previous studies in the Nehalem and Alsea basins, we showed that survival appears to be negatively correlated with flow in most releases, and in 2009 fork length was not correlated with survival. Our observations provide baseline information on factors that could influence smolt survival through the estuary as well as smolt to adult survival in these basins, and emphasize the importance of monitoring smolt survival in the estuary.

Stable oxygen and carbon isotope (δ18O and δ13C) analyses of otoliths are becoming increasingly common in fisheries science and management. However, little is known about the statistical properties of isotopic data and few attempts have been made to explore appropriate statistical methods that could be used for otolith data analysis. In this paper, we present a pilot study on δ18O and δ13C data from otoliths of two anadromous fish species, Atlantic salmon (Salmo salar) and Pacific sockeye salmon (Oncorhynchus nerka). The results indicated that the salmon otolith data were not normally distributed, so that linear discriminant function analysis and commonly-used statistical tests such as ANOVA and the t-test may not be appropriate. Using non-parametric k-sample nearest neighbor discriminant analysis, we were able to discriminate with high accuracy among five hatcheries for Atlantic salmon and the origins of wild and hatchery sockeye salmon. Analyses also indicated that the sample sizes required to estimate δ18O and δ13C means based on the different sources of variability (between group or within group) and precision levels (≤ ±5.0 %) were not large. These results and conclusions not only address the statistical considerations of isotopic data from otoliths, but also have practical importance for fisheries management as well.

The very successful 141 American Fisheries Society Annual Meeting was held in Seattle from September 4–8, 2011. During the meeting we organized an otolith symposium titled “Chemical signatures of otoliths and application in fisheries”. Twelve oral and three poster presenters from China, Japan, Norway, and United States were presented in the session, and contributed as manuscripts for publication in a special issue of Environmental Biology of Fishes. Why do we think this is important? First, the chemical signatures of otoliths have received increased attention in recent years because otoliths contain a great deal of information about the life history of the fish and that information can be extracted from stable isotope and trace elemental analyses. Second, although otolith chemistry has been investigated since the 1960s (e.g., Lowenstam 1961; McIntire 1963; Devereux 1967; Degens et al. 1969), very few symposia have concentrated specifically on the topic. Therefore, we think it is important and timely to highlight our AFS otolith symposium and publish the presentations. Otoliths are mm-sized, laminated calcium carbonate structures (CaCO3) found in the inner ears of teleost fish (Carlstrom 1963). They grow from a fluid medium (endolymph) that mainly contains calcium ions Ca and bicarbonate HCO3 (Schwarcz et al. 1998). From the mineralogical perspective, carbonates consist of 3 minerals: rhombohedral calcite and dolomite, and orthorhombic aragonite. Aragonite is unstable in nature and commonly inverts to its polymorph calcite (Nesse 1986). During the precipitation and physicochemical processes minor or trace elements are incorporated into carbonate mineral phases by substituting for Ca in the crystal structure. The divalent metal cation M in the calcite group occupies the octahedral sites with 6-fold coordination, whereas M in the aragonite group occupies the triangular sites with 9-fold coordination (Berry et al. 1983; Zheng 1999). Thus trace elements with larger ionic radii, such as Sr, Na, and Ba, are preferentially incorporated into orthorhombic aragonite, whereas rhombohedral calcite is enriched in smaller ions, such as Mg, Fe, Mn, Zn, and Cd. At normal or low temperature conditions this substitution is governed by a distribution coefficient (df) of a special trace element between liquid and solid phase that can be expressed by

Being able to individually follow fish

It is critical to study factors that are important for origin and maintenance of biological diversity. A comparative approach involving a large number of populations is particularly useful. We use this approach to study the relationship between ecological factors and phenotypic diversity in Icelandic Arctic charr (Salvelinus alpinus). Numerous populations of small benthic charr have evolved in lava springs in Iceland. These charr appear morphologically similar, but differ in important morphological features related to feeding. We found a clear relationship between diversity in morphology, diet, and ecological factors among populations. In particular, there were clear differences in morphology and diet between fish coming from habitats where the lava spring flowed on as a stream compared to habitats where the lava spring flowed into a pond. Our study shows that ecological factors are important for the origin and maintenance of biological diversity. The relationship between phenotype and ecological factors are observed on a fine scale, when comparing numerous populations that are phenotypically similar. This strongly suggests that for understanding, managing, and conserving biological diversity important ecological variables have to be taken into the account.

The optimism of early salmon hatchery practitioners toincrease abundance (Lichatowich 1999) has been tem-pered in recent decades by theoretical and empiricalstudiesindicatingunintendednegativeeffectshatcheriescanhaveonwildPacificsalmonandsteelhead(Naishetal. 2008; Pearsons and Temple 2010). Unintendedeffects of hatcheries are much more difficult and costlyto assess than evaluating the benefits of hatchery pro-duction to provide harvest opportunities. Holisticallyevaluating the relative costs and benefits of past andcurrent hatchery practices requires an understanding andestimation of the unintended effects (Pearsons 2010). Inrecent years, national and local governments, indigenous(e.g. First Nations or tribal) resource agencies, privateindustry and NGO conservation groups have begunefforts to reform public salmon and steelhead hatcherysystems in North America, which include critically eval-uating societal and biological risks and benefits.A significant number of national and internationalpolicy concernsandactions aredirectlyrelevantto thisissue. In the US Pacific Northwest, for example, theNational Oceanic and Atmospheric Administration(NOAA) is currently evaluating the environmentalimpact of salmon and steelhead hatcheries throughfederal mandates such as the Endangered Species Actand the Mitchell Act. The US State of Alaska is facedwith ongoing challenges of adhering to the State’sfisheries policies regarding sustainability, geneticsand escapement goals in the face of a growing privatesalmon hatchery industry in the State. In Canada, theDepartment of Fisheries and Oceans (DFO) is in theprocessofimplementinganambitiousnewWildSalmonPolicythatmustaddressimpactshatcherieshaveonwildsalmon. There is fresh thinking and emerging newinitiativesinbothJapanandRussiatoidentifyandseparately manage wild salmon in these nations.The growing demand for sustainable seafood hasput the global spotlight on salmon, which is near thetop of the list of most desired seafood, buoyed byreports of health benefits of eating salmon. Third partysustainability certifications of wild capture fisheries isrequired in many global markets, and Pacific salmon

We examined foraging adaptations and diet among dominant fishes within two species-rich riffle habitats in Thailand headwater rivers during the early and late portions of the dry season. All species exhibited diel temporal variations in feeding activity. Some species fed principally during daylight, while others fed mainly during darkness. Feeding patterns within species were generally spatially and temporally consistent. All seven fishes exploited the same benthic prey, but their foraging activities were related to spatially distinct water velocities. Diets overlapped with Ephemeroptera and Trichoptera the quantitatively most important prey. Ostracods, while not a large contributor to diet biomass, were numerically important in the diet of Homaloptera smithi. Trophic diversification through diel temporal feeding patterns and microhabitat separation by water velocity are major tactics in maintaining high diversity in riffle assemblages in Thai headwater rivers.

Morphologically divergent ecotypes arise in fish populations on postglacial time scales, and resource polymorphisms are often invoked to explain their origin. However, genetic recombination can constrain the ability of divergent selection to produce reproductive isolation in sympatry. Recombination breaks up favorable combinations of traits (”adaptive suites”) if indivi- dual traits are affected by different loci. Recombination also breaks up any association between traits under divergent selection and traits contributing to reproductive isolation. Thus, ecological speciation in the absence of preexisting barriers to gene flow is more likely when pleiotropy minimizes the number of loci involved. Here, we revisit research conducted by Carl Hubbs in the early 1900s on the effects of developmental rate on morphological traits in fishes. Hubbs’ work provides a mechanism to explain how sympatric divergence by trophic polymorphism can occur despite the challenges of recombination. We consider the implications of Hubbs’ observations for ecological speciation with gene flow in fishes, as well as rapid evolution in captive fish populations [Current Zoology 58 (1): 21–34, 2012].