Ultrasound imaging identifies life history variation in resident Cutthroat Trout.

Human activities that fragment fish habitat have isolated inland salmonid populations. This isolation is associated with loss of migratory life histories and declines in population density and abundance. Isolated populations exhibiting only resident life histories may be more likely to persist if individuals can increase lifetime reproductive success by maturing at smaller sizes or earlier ages. Therefore, accurate estimates of age and size at maturity across resident salmonid populations would improve estimates of population viability. Commonly used methods for assessing maturity such as dissection, endoscopy and hormone analysis are invasive and may disturb vulnerable populations. Ultrasound imaging is a non-invasive method that has been used to measure reproductive status across fish taxa. However, little research has assessed the accuracy of ultrasound for determining maturation status of small-bodied fish, or reproductive potential early in a species' reproductive cycle. To address these knowledge gaps, we tested whether ultrasound imaging could be used to identify maturing female Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi). Our methods were accurate at identifying maturing females reared in a hatchery setting up to eight months prior to spawning, with error rates ≤ 4.0%; accuracy was greater for larger fish. We also imaged fish in a field setting to examine variation in the size of maturing females among six wild, resident populations of Westslope Cutthroat Trout in western Montana. The median size of maturing females varied significantly across populations. We observed oocyte development in females as small as 109 mm, which is smaller than previously documented for this species. Methods tested in this study will allow researchers and managers to collect information on reproductive status of small-bodied salmonids without disrupting fish during the breeding season. This information can help elucidate life history traits that promote persistence of isolated salmonid populations.

Genetic and Morphological Characteristics in the Local Population of the Landlocked Salmon Oncorhynchus masou Originally Distributed in Kanagawa Prefecture, Japan.

Oncorhynchus masou, including subspecies of Oncorhynchus masou masou (yamame) and Oncorhynchus masou ishikawae (amago), is one of the salmonid groups impacted by human activity such as dam construction and release of non-native salmonids. In this study, we investigated the genetic structure of O. masou populations in the Sakawa and Sagami Rivers, Japan, by sequencing the mitochondrial control region. We hoped to identify genetically the O. masou populations specific to and originally native to Kanagawa Prefecture, where the two subspecies are thought to be present. The populations found in the upstream tributaries, where there has been no human impact and no upstream migration of fishes, were assumed to be descendants of the local O. masou populations in both river systems, and the morphological features seen here were similar to amago and yamame. However, both populations were genetically related to amago. In addition, only six haplotypes were detected in 315 individuals collected from 20 localities in the two river systems. Furthermore, haplotype diversity and nucleotide diversity of these populations were low, and high FST values were observed. These results suggest that the population size is restricted and genetic diversity is decreasing in the O. masou populations of the Sakawa and Sagami Rivers.

Size, age, growth and site fidelity of anadromous cutthroat trout Oncorhynchus clarkii clarkii in the Salish Sea.

Pacific salmon Oncorhynchus spp. have been the focus of scientific research for over a century, but anadromous trout in this genus, in particular anadromous coastal cutthroat trout Oncorhynchus clarkii clarkii, have been neglected. Oncorhynchus clarkii clarkii occupy a diverse range of habitats including fresh water, brackish estuaries and marine water, but have a relatively small home range making them ideal for studies of behaviour and movements during ocean residency. In 2015, we sampled O. c. clarkii monthly along a small stretch of beach (47.08° N, 122.98° W) in Eld Inlet, south Puget Sound, Washington using a beach seine. We collected tissue for genetic tagging and stock identification and scales for aging from 427 O. c. clarkii, ranging in size from 118 to 478 mm fork length. Additionally, we enumerated redds in natal streams of those fish tagged to describe inter-habitat movement patterns and investigate site fidelity of juvenile and adult O. c. clarkii in the marine environment. Consistent with other anadromous salmonids, O. c. clarkii captured at our study beach exhibited rapid growth rates, particularly in spring following dispersal into the marine environment (mean ± SD = 0.61 ± 0.29 mm-d ). Genetic tag data revealed that while O. c. clarkii undergo inter-estuarine migrations, O. c. clarkii of all life stages exhibited site fidelity in the marine environment. Twenty-one percent (64/305) of sampled O. c. clarkii were recaptured at least once during the course of the study while multiple fish (n = 3) were recaptured up to five times. These results suggest that O. c. clarkii occupying south Puget Sound reside in or regularly return to a small geographic area in the nearshore environment for much of their life and therefore may be particularly vulnerable to anthropogenic disturbance (development, angling, etc.).

Validity of inferring size-selective mortality and a critical size limit in Pacific salmon from scale circulus spacing.

Size-selective mortality owing to lack of energy reserves during the first marine winter has been suggested to be a result of juvenile salmon failing to reach a critical size or condition by the end of their first marine summer and not surviving the following winter due to this presumed energy deficit. This hypothesis implies strong size dependency of mortality, and is subject to empirical data support for acceptance. Scale circulus spacing has been interpreted as an index for body size, and we reviewed the effect of size-selective mortality with a knife-edge mortality function on descriptive statistics for a scale circulus spacing index (SCSI). In order to invoke size selection as an important driver of mortality during the first year of ocean rearing, it is necessary to demonstrate not only that size-selective mortality is directed towards the smaller members of the population, but that the selective nature of the mortality can account for a substantial portion of the observed mortality. If the assumption is made that a random sample of a single juvenile population has been obtained, then studies that employ a SCSI to infer size-selective mortality coupled with a critical size limit must demonstrate a shift toward larger values of the SCSI, but also a concomitant reduction in the variance and range of the SCSI and an increase in the skewness and kurtosis of the SCSI values. Through simulation we found that the percentage of adults that displayed a SCSI value greater than the maximum observed in the juvenile sample was highly dependent on the initial juvenile sample size and size-selective mortality rate. Geographical distributions of juvenile Pacific salmon can be stratified by size, with larger individuals migrating earlier from local ocean entry locations than smaller individuals, and thus differential timing migration of juveniles based upon body size prior to the collection of the marine juvenile sample may be a more plausible explanation of published trends in the SCSI, rather than invoking substantial size-selective mortality and a critical size limit.

Comparative anatomy of the dorsal hump in mature Pacific salmon.

Mature male Pacific salmon (Genus Oncorhynchus) demonstrate prominent morphological changes, such as the development of a dorsal hump. The degree of dorsal hump formation depends on the species in Pacific salmon. It is generally accepted that mature males of sockeye (O. nerka) and pink (O. gorbuscha) salmon develop most pronounced dorsal humps. The internal structure of the dorsal hump in pink salmon has been confirmed in detail. In this study, the dorsal hump morphologies were analyzed in four Pacific salmon species inhabiting Japan, masu (O. masou), sockeye, chum (O. keta), and pink salmon. The internal structure of the dorsal humps also depended on the species; sockeye and pink salmon showed conspicuous development of connective tissue and growth of bone tissues in the dorsal tissues. Masu and chum salmon exhibited less-pronounced increases in connective tissues and bone growth. Hyaluronic acid was clearly detected in dorsal hump connective tissue by histochemistry, except for in masu salmon. The lipid content in dorsal hump connective tissue was richer in masu and chum salmon than in sockeye and pink salmon. These results revealed that the patterns of dorsal hump formation differed among species, and especially sockeye and pink salmon develop pronounced dorsal humps through both increases in the amount of connective tissue and the growth of bone tissues. In contrast, masu and chum salmon develop their dorsal humps by the growth of bone tissues, rather than the development of connective tissue.

Interpopulation Comparison of Sex-Biased Mortality and Sexual Size Dimorphism in Sea-Run Masu Salmon, Oncorhynchus masou.

Evolutionary ecologists often expect that natural and sexual selection result in systematic co-occurrence patterns of sex-biased mortality and sexual size dimorphism (SSD) within animal species. However, whether such patterns actually occur in wild animals is poorly examined. The following expectation, the larger sex suffers higher mortality, was primarily tested here for apparently native sea-run masu salmon (Oncorhynchus masou) in three populations in Hokkaido, Japan. Field surveys on sex ratios, body sizes, and ages of smolts and returning adults revealed that two of the three populations exhibited an expected pattern, a female-biased marine mortality and SSD, but one population demonstrated an unexpected co-occurrence of male-biased marine mortality and female-biased SSD. These female-biased SSDs were attributed to faster marine growth of females because of no sex difference in smolt body size. It has been previously suggested that breeding selection favoring large size generally act more strongly in females than in males in Japanese anadromous masu, as there is a weak sexual selection on adult males but universally intensive natural selection on adult females. Thus, this hypothesis explains female-biased SSDs well in all study populations. Interpopulation variation in sex-biased mortality found here might result from differences in marine predation and/or fishing pressures, given that selection driving female-biased SSD makes females forage more aggressively than males during the marine phase. Taken together, these results raise the possibility that evolutionary forces have shaped adaptive sex-specific foraging strategies under relationships between growth and mortality, resulting in co-occurrence patterns of sex-biased mortality and SSD within animal species.

[Heritability of body weight and fork length for Oncorhynchus masou masou].

Body weight and body length have been considered as the most important production traits for the fish genetic improvement. For cold-water fish, body length was usually substituted by fork length. In order to estimate the heritability of body weight and fork length of the sixth generation Oncorhynchus masou masou, which was introduced into China, the method of unbalanced nest design and an artificial insemination technigue were used. Twenty-nine full-sib families and fourteen half-sib families were obtained. Body weight and fork length of O. masou masou were measured in 12 and 24 months after fertilization. Based on full-sib and half-sib families data, the causal components of phenotypic variance were calculated. The results showed that, (1) during the whole growth phase of O. masou masou, the coefficient variation (CV) of fork length was higher than body weight, and CV of 12-month old was higher than that of 24-month old; (2) body weight and fork length of O. masou masou among sires and dams among sires were significant difference (P<0.01) both at 12 months and at 24 months; (3) the maternal component estimates were significantly larger than those of paternal ones for body weight and fork length traits both at 12 months and at 24 months; (4) for 12 months of O. masou masou the heritabilities of body weight and fork length were 0.41~0.51 and 0.46~0.54, respectively. For 24 months the values were 0.55~0.60 and 0.53~0.59, respectively; and (5) it was concluded that the heritability of growth traits in O. masou masou was relatively high and this highlights the potential to improve its growth through selective breeding. This study shows important data supporting for further genetic improvement of O. masou masou.

[Gaseous intermediates in the brain of the salmon Oncorhynchus masou].

Distribution of nitroxidergic and H2S-producing neurons in the brain of the salmon Oncorhynchus masou was studied by methods of histochemical markering of NADPH-diaphorase and by immunohistochemical markering of the neuronal nitric oxide synthase and cystathionin beta-synthase (CBS). The established distribution of CBS and nNOS/NADPH-d of neurons and fibers in the salmon telencephalon, optic tectum, and cerebellum allows suggesting that the NO- and H2S-producing systems, represent individual, non-overlapping neuronal complexes performing specialized functions in the activity of local neuronal networks. In the brainstem part, the nNOS-ir and NADPH-d-positive neurons were detected in the composition of viscerosensor (V, VII, and IX-X) and visceromotor (III, IV, and VI) nuclei of craniocerebral nerves, octavolateral afferent complex, reticulospinal neurons, and medial reticular formation. CBS in the salmon medulla was revealed in neurons of the X nerve nucleus, reticulospinal neurons, and ventrolateral reticular formation. Distribution of NO-ergical and H2S-producing neurons in the salmon medulla nuclei indicates that NO in salmon is the predominant neuromodulator of medulla viscerosensory systems, while H2S seems to modulate only the descending motor systems. The results of the performed study allow suggesting that NI in the descending motor systems. The results of the performed study allow suggesting that NO in the salmon medulla periventricular area can act as a regulator of postnatal ontogenesis.

Variable incidences and morphological characteristics of female masu salmon Oncorhynchus masou with growth hormone pseudogene.

The genetic sex of mature masu salmon Oncorhynchus masou (212 males and 243 females) collected from three rivers located in the mid-western part of Hokkaido was determined using the male-specific genetic marker growth hormone pseudogene (GHp). A total of 72 phenotypic females were found to have GHp, whereas none of the phenotypic males lacked GHp. The occurrence of females with incongruence between genotypic and phenotypic sex varied with the river and reached the highest rate of 67%. In contrast, none of the phenotypic males were found to have a female genotype. Comparison of adult body size showed that females with GHp were significantly smaller than those without GHp. Moreover, comparison of secondary characteristics revealed that both upper jaw length and head length were greater in females with GHp than in those without GHp. These results suggest that genetic changes (e.g. transposition and mutation) may also affect morphological characteristics.

Eco-evolutionary dynamics in Pacific salmon.

Increasing acceptance of the idea that evolution can proceed rapidly has generated considerable interest in understanding the consequences of ongoing evolutionary change for populations, communities and ecosystems. The nascent field of 'eco-evolutionary dynamics' considers these interactions, including reciprocal feedbacks between evolution and ecology. Empirical support for eco-evolutionary dynamics has emerged from several model systems, and we here present some possibilities for diverse and strong effects in Pacific salmon (Oncorhynchus spp.). We specifically focus on the consequences that natural selection on body size can have for salmon population dynamics, community (bear-salmon) interactions and ecosystem process (fluxes of salmon biomass between habitats). For example, we find that shifts in body size because of selection can alter fluxes across habitats by up to 11% compared with ecological (that is, numerical) effects. More generally, we show that selection within a generation can have large effects on ecological dynamics and so should be included within a complete eco-evolutionary framework.

[Structure of the retina of Pacific salmon fry in twilight illumination during the geomagnetic field changes].

The retinomotor response of the masu salmon Oncorhynchus masou fry retina was studied under the conditions of mesopic (twilight) illumination after experimental geomagnetic field (GMF) compensation which was reached using the Helmholtz coils. In the control group, the retinomotor response of masu salmon fry to twilight illumination was usual: the nuclei of the neurosensory rod cells were located immediately above the external limiting layer, while the nuclei of the neurosensory cone cells were displaced closer to the pigment epithelium. After experimental GMF compensation, the masu salmon fry retina reaction was unusual: the neurosensory cone cell nuclei adhered to the external limiting membrane, while the nuclei of the neurosensory rod cells were displaced closer to the pigment epithelium layer. Double and central neurosensory cone cells occupied the position that was inadequate to normal reaction to twilight: the bodies of these cells were considerably elongated, and the external segments reached the pigment epithelium layer. Thus, in the experiment with GMF compensation, we have found the unusual structure of the retina, which only vaguely corresponded to a reaction to mesopic adaptation. The results suggest, that the visible light is not a unique variety of the electromagnetic field, that could be perceived by the fish retina.

Interaction between neuropeptide Y immunoreactive neurons and galanin immunoreactive neurons in the brain of the masu salmon, Oncorhynchus masou.

We investigated the immunohistochemical localization of neuropeptide Y (NPY) and galanin (GAL) in the brain of the masu salmon Oncorhynchus masou in order to clarify the interaction between these neuropeptide hormones in the brain. NPY-immunoreactive (ir) cell bodies were observed in the ventral and lateral regions of the ventral telencephalon (Vv and Vl, respectively), and in the dorsolateral midbrain tegmentum. NPY-ir fibers were observed throughout the brain, mainly in the ventral telencephalon, hypothalamus, optic tectum, and midbrain. GAL-ir cell bodies were observed in the nucleus preopticus parvicellularis anterioris (PPa) and the ventral zone of the periventricular hypothalamus (Hv). Both GAL-ir and NPY-ir fibers were observed throughout the brain. Furthermore, we examined the interaction between the NPY neurons and GAL neurons by performing double-staining immunohistochemistry. Some GAL-ir fibers were in close contact with the NPY-ir cell bodies in the Vv and Vl. In addition, some NPY-ir fibers were in close contact with the GAL-ir cell bodies in the PPa and Hv. These findings suggest that reciprocal connections exist between the NPY neurons and GAL neurons in the brain of the masu salmon.

[Ultrastructural study of spermatogenesis in silversides Oncorhynchus kisutch and cherry salmon O. masou (Salmonidae, Teleostei)].

Spermatogenesis in the silversides Oncorhynchus kisutch and cherry salmon O. masou, was investigated by transmission electron microscopy. It has been shown that male germ cells of both species had no difference in dimensional and ultrastructural parameters. The characteristic feature of spermatogonia was the presence of germ determinant substance, a cytoplasmic barker of sex line cells. Primary and secondary spermatocytes, as well as early spermatids were arranged in clusters consisted of synchronously developing cells. The spermiogenesis was peculiar in arising of electron-lucent vesicle which formed a structural complex with apical dense part of nuclear envelope. This complex has clear similarity with unformed spermatid acrosomes in many Metazoa and has been termed by the authors as an acrosome-like structure (AS). Disappearance of AS occurring at the final stage of the spermiogenesis allows considering AS as a temporary existing structure recapitulating the ancestral morphotype of salmonid sperm. Spermatozoa of both species are typical acrosome lacking cells which are characteristic of many representatives of Teleostei having external fertilization.

Latitudinal variation in sexual size dimorphism of sea-run masu salmon, Oncorhynchus masou.

Sexual size dimorphism (SSD), a difference in body size between the sexes, occurs in many animal species. Although the larger sex is often considered invariable within species, patterns of selection may result in interpopulation variation or even reversal of SSD. We evaluated correlations between latitude and female body size, male body size, and relative body size (male body size/female body size) in 22 populations (ranging from 37 degrees N to 49 degrees N) of sea-run masu salmon (Oncorhynchus masou) that spawn in rivers along the Sea of Japan coast. Male size and the relative body size increased with latitude, but female size did not correlate with latitude. In addition, increase in male size with latitude was sufficient to result in a reversal of SSD, the switch-point being around 45 degrees N. We suggest that the positive correlation between latitude and male size is due to increasing operational sex ratios or sexual selection on sea-run male body size that result from sex-biased patterns of anadromy. In conclusion, our study provides the first example of predictable geographic variation in SSD shaped by apparent patterns of sexual selection.

Morphological characteristics of the retinomotor response in salmon trout (oncorhynchus masou) fry in a magnetic field and red light.

The retinomotor response was studied in fry of the salmon trout Oncorhynchus masou during experimental exposures to a constant magnetic field and red light alone and together. The responses of photoreceptors and the pigmented epithelium to red light were mesopic in nature. The mesopic state of the retina after exposure of fish to a magnetic field in the dark differed from the pigment epithelium response after exposure to red light. On exposure to the magnetic field after red light, the effects of these two treatments were additive. Rods adapted to low-light conditions, while cones adapted to light. The simultaneous operation of these two mechanisms of perception is thus possible, although it never occurs in normal conditions. On exposure to red light after the magnetic field, the retinomotor response reflected a physiological dysfunction in which neither rods nor cones were operative. The pigmented epithelium is actively involved in responses to changes in the magnetic field. It is suggested that cells of the pigmented epithelium can function as light-sensitive magnetoreceptors.

Life-history variation and allometry for sexual size dimorphism in Pacific salmon and trout.

Allometry for sexual size dimorphism (SSD) is common in animals, but how different evolutionary processes interact to determine allometry remains unclear. Among related species SSD (male : female) typically increases with average body size, resulting in slopes of less than 1 when female size is regressed on male size: an allometric relationship formalized as 'Rensch's rule' . Empirical studies show that taxa with male-biased SSD are more likely to satisfy Rensch's rule and that a taxon's mean SSD is negatively correlated with allometric slope, implicating sexual selection on male size as an important mechanism promoting allometry for SSD. I use body length (and life-history) data from 628 (259) populations of seven species of anadromous Pacific salmon and trout (Oncorhynchus spp.) to show that in this genus life-history variation appears to regulate patterns of allometry both within and between species. Although all seven species have intraspecific allometric slopes of less than 1, contrary to expectation slope is unrelated to species' mean SSD, but is instead negatively correlated with two life-history variables: the species' mean marine age and variation in marine age. Second, because differences in marine age among species render SSD and body size uncorrelated, the interspecific slope is isometric. Together, these results provide an example of how evolutionary divergence in life history among related species can affect patterns of allometry for SSD across taxonomic scales.

Biotechnology: surrogate broodstock produces salmonids.

A worldwide decline in the number of wild salmonids calls for strategies to restore endangered populations. Here we show that germ cells can be transplanted between two different salmonid species, with the subsequent production of xenogenic, donor-derived offspring. This pioneering xenotransplantation technology may eventually find applications in facilitating the production of commercially valuable fish, as well as in species conservation.

[Magnetic field induced structural changes of Oncorhynchus masou retina ]. / Morfologicheskie izmeneniia v setchatke molodi simy Oncorhynchus masou pri éksperimental'nom izmenenii magnitnogo polia.

The work describes the retinomotor response of Oncorhynchus masou young kept at illumination ranging from 1 to 10 lux, exposed to a field of a permanent magnet, and under conditions of geomagnetic field compensation. Retinomotor response in young exposed to magnetic field in darkness corresponds to partial light adaptation. During the exposure to a field of a permanent magnet the pigment was found to concentrate in pigmentocyte processes endings, forming the layer, that subdivided cone outer segments and rod outer segments and ellipsoids. Pigment in an aggregated state poorly shielded rod outer segments. In experiments with geomagnetic field compensation in darkness double and central cones were significantly elongated, the pigment is concentrated in initial parts of the processes and in pigmentocyte bodies. Pigment demonstrates the reaction that is similar to darkness adaptation, while the state of photoreceptors corresponds to a partial light adaptation. The changes of a natural magnetic field were accompanied by unusual retinomotor responses, in which the state of photoreceptors and retinal pigment epithelium did not correspond to photopic, mesopic or scotopic adaptation.

[Morphology of retinomotor response of Oncorhynchus masou fry exposed in magnetic field and red light]. / Morfologicheskie osobennosti retinomotornoi reaktsii u moldi simy (Oncorhynchus masou) v magnitnom pole i krasnom svete.

The retinomotor response of Oncorhynchus masou fry was studied following their experimental exposure to constant magnetic field, red light and their combination. Photoreceptor and pigment epithelium reactions to red light had a mesopic character. The mesopic state of retina after exposure of fishes to magnetic field in darkness differed from that after exposure to red light by the reaction of a pigment epithelium (PE). Exposure to magnetic field after red light resulted in the summation of these two effects. As rods are adapted to twilight, and cones are adapted to light, combined functioning of two perception mechanisms is possible, which is never found in normal conditions. After exposure to red light that followed the action of magnetic field, retinomotor reaction reflected the physiological dysfunction, with no functioning of either rods or cones. PE was actively participating in reactions to changes of magnetic field. The assumption that the cells of PE of fish retina can act as a light-dependent magnetoreceptor, is discussed.

[Morphological changes in the parr masou salmon Oncorhynchus masou retina in experimental change of geomagnetic field]. / Morfologicheskie izmeneniia v setchatki molodi simy Oncorhynchus masou pri éksperimental'nom izmenenii geomagnitnogo polia.

Topography of photoreceptor cells in young salmon Oncorhynchus masou retina, their properties and morphology of cellular organelles in external and internal segments of photoceptors have been first described. Morphological changes of retina cells were analysed in day and night time, and also in the experiment for indemnification of geomagnetic field (GMF) in the body of the aquarium. A comparison of retina structure in fishes of night and day time controls with that in experimental fishes has shown that the external cone segments in the latter occupy, in relation to the external limiting membrane, an intermediate position, characteristic of retinae exposed to twilight lighting. It is supposed that GMF indemnification was equivalent to weak light pulse, which, however, could considerably change melatonin production by retina photoreceptor cells. Thus, at experimental indemnification of GMF, retina sensitive cells demonstrate typical retinomotor response. Some ultrastructural changes in retina cells were also detected, in particular, size changes in ribbon synapses in rod and cone terminations. In addition, nematosomes appeared in the internal nuclear layer, and in the spinules, i.e. digitiform invaginations of terminal dentrites of horizontal cells into cone nervous terminations, the quantity of an electron dense material was noticeably magnified in comparison with a night control. The noted changes testify, in our opinion, to essential modifications in metabolic processes of retina photoreceptors under effect of GMF variations, in particular, to changes in retinal melatonin synthesis.