Identification of the sex chromosome pair in chum salmon (Oncorhynchus keta) and pink salmon (Oncorhynchus gorbuscha)

Fluorescence in situ hybridization (FISH) using a probe to the male-specific GH-Y (growth hormone pseudogene) was used to identify the Y chromosome in the karyotypes of chum salmon (Oncorhynchus keta) and pink salmon (Oncorhynchus gorbuscha). The sex chromosome pair is a small acrocentric chromosome pair in chum salmon and the smallest metacentric chromosome pair in pink salmon. Both of these chromosome pairs are morphologically different from the sex chromosome pairs in chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch). The 5S rRNA genes are on multiple chromosome pairs including the sex chromosome pair in chum salmon, but at the centromeres of two autosomal metacentric pairs in pink salmon. The sex chromosome pairs and the chromosomal locations of the 5S rDNA appear to be different in all five of the North American Pacific salmon species and rainbow trout. The implications of these results for evolution of sex chromosomes in salmonids are discussed.     

Diagnostic single nucleotide polymorphisms for identifying westslope cutthroat trout (Oncorhynchus clarki lewisi), Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) and rainbow trout (Oncorhynchus mykiss)

We describe 12 diagnostic single nucleotide polymorphism (SNP) assays for use in species identification among rainbow and cutthroat trout: five of these loci have alleles unique to rainbow trout (Oncorhynchus mykiss), three unique to westslope cutthroat trout (O. clarkii lewisi) and four unique to Yellowstone cutthroat trout (O. clarkii bouvieri). These diagnostic assays were identified using a total of 489 individuals from 26 populations and five fish hatchery strains.     

Parvicapsula minibicornis in anadromous sockeye (Oncorhynchus nerka) and coho (Oncorhynchus kisutch) salmon from tributaries of the Columbia River

The myxosporean parasite Parvicapsula minibicornis is described from adult sockeye and coho salmon during spawning migrations in tributaries of the Columbia River in Canada and the United States. These observations extend the known distribution of this parasite from the Fraser River drainage basin. The parasite was identified in Columbia River salmonids using polymerase chain reaction (PCR) and by in situ hybridization, but unlike in Fraser River salmon, it was not observed in conventional histological preparations of the kidney. Prevalence of the parasite determined by PCR was higher in spawning sockeye from the Fraser River than in those from the Okanagan River. Our ability to explain the relatively low prevalence and absence of clinical P. minibicornis infections in Columbia River salmon is hampered by our poor understanding of the life cycle of this parasite.     

A genetic analysis of early development in pink (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) at three different temperatures

A factorial mating design was employed in which five males were mated to each of five females in each of two stocks for both pink and chum salmon. The resulting embryos and alevins were incubated at constant water temperatures of 4, 8, and 16 degrees C for pink salmon and 3, 8, and 15 degrees C for chum salmon. Variation among families in alevin and fry survival rates, hatching, button-up time, length, and weight was the least at 8 degrees C. Heritability of traits directly correlated with fitness, such as survival rates and button-up time, was low at all temperatures (h2 less than or equal to 0.25). Maternal effects could account for a substantial portion of the variation in alevin and fry size characters. Nonadditive genetic variance accounted for more of the variation in fry size characters than in those of alevins. Negative genetic correlations were observed between embryo survival and subsequent alevin size and between hatching time and subsequent alevin and fry size. Genotype-temperature interactions could underlie a substantial amount of phenotypic variation in the developmental characters examined for both species.     

Rainbow trout (Oncorhynchus mykiss) neuropeptide Y.

Neuropeptide Y (NPY) has been isolated from brain extracts of the rainbow trout (Oncorhynchus mykiss) and subjected to structural analyses. Plasma desorption mass spectroscopy estimated the molecular mass of the purified peptide as 4303.9 Da. Automated Edman degradation unequivocally established the sequence of a 36 amino acid residue peptide as: Tyr-Pro-Pro-Lys-Pro-Glu-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Pro-Glu-Glu-Leu-Ala-Lys-Tyr-Tyr-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-Gln-Arg-Tyr. The molecular mass calculated from this sequence (4304 Da) is consistent with that obtained by mass spectroscopy. The presence of a C-terminal amide was established by radioimmunoassay. Rainbow trout NPY is identical in primary structure to coho salmon (Oncorhynchus kisutch) pancreatic polypeptide (PP). These data may indicate that, in this group of salmonid fishes, a single member of the NPY/PP peptide family is expressed in both neurons and peripheral endocrine cells.     

Ubiquitin genes in rainbow trout (Oncorhynchus mykiss)

Ubiquitin is a small protein involved in intracellular proteolysis. It is highly conserved throughout eukaryotic phyla and has been detected in such diverse species as yeast, barley, Drosophila and man. A previous study showed that chromatin of rainbow trout testis contains free ubiquitin with a sequence similar to that of other phyla. In the present study, which focused on rainbow trout but included eleven other species, it is shown that fish ubiquitin genetic organisation and expression are similar to those of other phylogenetic groups through the following set of observations: (a) Multiple loci were detected, (b) These loci encode repeats of ubiquitin, (c) Although the DNA sequences are not conserved, the encoded amino acid sequences are fully conserved, (d) The expression of ubiquitin was influenced by cell culture conditions and viral infection.     

Characterization of coho salmon (Oncorhynchus kisutch) insulin

Insulin has been isolated from islet tissue of coho salmon (Oncorhynchus kisutch) by gel filtration and HPLC and the complete amino acid sequence has been determined. The sequence differs from bovine insulin at 14 sites but all interchanges are conservative from the viewpoint of preservation of conformation. A comparison of insulin sequences from other fish is presented. Salmon insulin cross-reacts very weakly with antiserum to bovine insulin and vice versa. A completely homologous radioimmunoassay has been developed and used to estimate the insulin in salmon islet tissue and in plasma. The hypoglycemic effect of salmon insulin in salmon was more pronounced and persisted longer than that caused by identical doses of bovine insulin.     

Population genomics and conservation of Gila Trout (Oncorhynchus gilae)

Conservation Genetics - Many salmonid species exist in highly structured and isolated populations, and are susceptible to habitat fragmentation and disturbances. Gila Trout (Oncorhynchus gilae) is...     

Diel movements of out-migrating Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) smolts in the Sacramento/San Joaquin watershed

We used ultrasonic telemetry to describe the movement patterns of late-fall run Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss) smolts during their entire emigration down California’s Sacramento River, through the San Francisco Bay Estuary and into the Pacific Ocean. Yearling hatchery smolts were tagged via intracoelomic surgical implantation with coded ultrasonic tags. They were then released at four upriver locations in the Sacramento River during the winters of 2007 through 2010. Late-fall run Chinook salmon smolts exhibited a nocturnal pattern of migration after release in the upper river. This is likely because individuals remain within a confined area during the day, while they become active at night and migrate downstream. The ratio between night and day detections of Chinook salmon smolts decreased with distance traveled downriver. There was a significant preference for nocturnal migration in every reach of the river except the Estuary. In contrast, steelhead smolts, which reside upriver longer following release, exhibited a less pronounced diel pattern during their entire migration. In the middle river, Delta, and Estuary, steelhead exhibited a significant preference for daytime travel. In the ocean Chinook salmon preferred to travel at night, yet steelhead were detected on the monitors equally during the night and day. These data show that closely related Oncorhynchus species, with the same ontogenetic pattern of out-migrating as yearlings, vary in migration tactic.     

Sympatric, simultaneous, and random mating between markless trout (iwame; Oncorhynchus iwame) and red-spotted masu salmon (amago; Oncorhynchus masou ishikawae)

The markless trout (iwame, Oncorhynchus iwame) has long been suspected not to be an independent species, but rather a markless mutant form of the red-spotted masu salmon (amago, O. masou ishikawae). Nevertheless, no field study has examined this issue. Here we report a field study on the reproductive ecology of iwame and amago coexisting in the upper stream of the Inabe River. We found that iwame and amago mate sympatrically, simultaneously, and randomly, and observed five cases of heterogeneous oviposition between the two. Our results suggest that no pre-mating reproductive isolation exists between iwame and amago. Because previous studies have shown the absence of post-mating isolation, we propose that iwame and amago are the same species. Iwame should be considered as a markless form of the red-spotted masu salmon, and O. iwame as a junior synonym of O. masou ishikawae.     

Dorsal hump morphology in pink salmon (Oncorhynchus gorbuscha)

Mature male Pacific salmon (Genus Oncorhynchus) develop a dorsal hump, as a secondary male sexual characteristic, during the spawning period. Previous gross anatomical studies have indicated that the dorsal humps of salmon are mainly composed of cartilaginous tissue (Davidson [1935] J Morphol 57:169–183.) However, the histological and biochemical characteristics of such humps are poorly understood. In this study, the detailed microstructures and components of the dorsal humps of pink salmon were analyzed using histochemical techniques and electrophoresis. In mature males, free interneural spines and neural spines were located in a line near to the median septum of the dorsal hump. No cartilaginous tissue was detected within the dorsal hump. Fibrous and mucous connective tissues were mainly found in three regions of the dorsal hump: i) the median septum, ii) the distal region, and iii) the crescent‐shaped region. Both the median septum and distal region consisted of connective tissue with a high water content, which contained elastic fibers and hyaluronic acid. It was also demonstrated that the lipid content of the dorsal hump connective tissue was markedly decreased in the mature males compared with the immature and maturing males. Although, the crescent‐shaped region of the hump consisted of connective tissue, it did not contain elastic fibers, hyaluronic acid, or lipids. In an ultrastructural examination, it was found that all of the connective tissues in the dorsal hump were composed of collagen fibers. Gel electrophoresis of collagen extracts from these tissues found that the collagen in the dorsal hump is composed of Type I collagen, as is the case in salmon skin. These results indicate that in male pink salmon the dorsal hump is formed as a result of an increase in the amount of connective tissue, rather than cartilage, and the growth of free interneural spines and neural spines. J. Morphol. 275:514–527, 2014. © 2013 Wiley Periodicals, Inc.     

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

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

Multigenerational outbreeding effects in Chinook salmon (Oncorhynchus tshawytscha)

Outbreeding, mating between genetically divergent individuals, may result in negative fitness consequences for offspring via outbreeding depression. Outbreeding effects are of notable concern in salmonid research as outbreeding can have major implications for salmon aquaculture and conservation management. We therefore quantified outbreeding effects in two generations (F₁ hybrids and F₂ backcrossed hybrids) of Chinook salmon (Oncorhynchus tshawytscha) derived from captively-reared purebred lines that had been selectively bred for differential performance based on disease resistance and growth rate. Parental lines were crossed in 2009 to create purebred and reciprocal hybrid crosses (n = 53 families), and in 2010 parental and hybrid crosses were crossed to create purebred and backcrossed hybrid crosses (n = 66 families). Although we found significant genetic divergence between the parental lines (F_ST = 0.130), reciprocal F₁ hybrids showed no evidence of outbreeding depression (hybrid breakdown) or favorable heterosis for weight, length, condition or survival. The F₂ backcrossed hybrids showed no outbreeding depression for a suite of fitness related traits measured from egg to sexually mature adult life stages. Our study contributes to the current knowledge of outbreeding effects in salmonids and supports the need for more research to better comprehend the mechanisms driving outbreeding depression.     

Retinal projections in sockeye salmon smolts (Oncorhynchus nerka)

Summary The retinal projections in 2-year-old salmon smolt (Oncorhynchus nerka) are significantly different from those observed in other teleosts examined to date in that the projections are more extensive. Very noticeable are extensive projections to most of the dorsal thalamus, to all layers of the optic tectum, and into the periaqueductal gray of the torus semicircularis. The salmon smolt has bilateral retinal projections to the diencephalon and pretectum. A small retinal projection to the lateral habenular nucleus has not been described previously. Although these findings suggest striking differences in retinal projections among teleosts, this variation may relate to age differences since the previously studied teleosts were adults.     

Lectin histochemistry of rainbow trout (Oncorhynchus mykiss) gill and skin

In order to characterize the glycoconjugate residues in skin and gills of the adult rainbow trout, the binding pattern of five biotinylated lectins with different carbohydrate specificities was examined. In the skin, mucous cells revealed binding sites for PNA and SBA; filament-containing cells were additionally labelled with Con A. However, the basal cell layer showed no reaction. In the gill, subpopulations of mucous cells reacted with Con A, PNA, SBA and UEA-I. This broader spectrum of glycoconjugates in gill mucous cells compared with the epidermal mucous cells could point to the additional function of gill mucus in ion and osmoregulation. Lectin binding sites were less common in the respiratory epithelial cells of the secondary lamellae than in those of the primary lamellae. Chloride cells revealed mannose, galactose and fucose residues. Immature chloride cells, as indicated by a comparison with Na⁺/K⁺ ATPase immunolabelling, reacted with Con A; subpopulations of them reacted with PNA, SBA and UEA-I. The results form the basis for further investigations in which these cell populations can be analysed under different environmental conditions