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Copper (Cu) is an essential trace mineral for the growth of most farmed fish species. Since natural water typically contains low Cu levels, exogenous Cu supplementation may be required in intensive aquaculture systems to meet the nutritional requirements of certain fish species. A 10-week feeding experiment was conducted to evaluate the Cu requirement on growth performance, tissue Cu content, hematological parameters and anti-oxidant responses in coho salmon Oncorhynchus kisutch (Walbaum, 1792). In this experiment, six experimental diets supplemented with graded Cu (CuSO 4 used as Cu source) contents (0.20, 2.10, 3.70, 5.80, 7.75, and 9.85 mg/kg) to feed the fish (180.22 ± 0.41 g). Total 180 fish were randomly distributed across 18 individuals tank (10 fish/cage, water volume 1,000-L) fed three times a day. The result showed that the mortality and morphological indices were completely unaffected by the increasing Cu supplementation in the diet ( P  > 0.05). Whereas, the non-supplemented diet (0.20 mg Cu/kg) had a poor growth performance of the fish ( P  < 0.05), including the lowest final body weight and specific growth rate, the highest feed conversion ratio. No significant differences ( P  > 0.05) were observed in the proximate composition of muscle across graded dietary copper levels. However, increasing dietary Cu level induced Cu accumulation ( P  < 0.05), but higher Cu level in the diet (> 5.8 mg/kg) did not further increase of muscle and liver in coho salmon. Compared with the 0.20 Cu mg/kg in diet, the supplemented diet enhanced the antioxidant capacity in liver and serum, and decrease the content of malondialdehyde in liver ( P  < 0.05). Diet with 0.20-5.80 mg/kg supplemental Cu significantly increased the serum alkaline phosphatase and lysozyme activities, decrease the serum alanine aminotransferase and aspartate aminotransferase activities ( P  < 0.05), while higher dietary Cu level (> 5.8 mg/kg) showed the opposite trend. The broken-line analysis based on specific growth rate, liver Cu accumulation, copper-zinc superoxide dismutase in liver and serum, the appropriate dietary Cu level for coho salmon were estimated to be 5.29–5.92 mg/kg.

Background Transcriptomic responses to immune stimulation were investigated in coho salmon ( Oncorhynchus kisutch ) with distinct growth phenotypes. Wild-type fish were contrasted to strains with accelerated growth arising either from selective breeding (i.e. domestication) or genetic modification. Such distinct routes to accelerated growth may have unique implications for relationships and/or trade-offs between growth and immune function. Results RNA-Seq was performed on liver and head kidney in four ‘growth response groups’ injected with polyinosinic-polycytidylic acid (Poly I:C; viral mimic), peptidoglycan (PGN; bacterial mimic) or PBS (control). These groups were: 1) ‘W’: wild-type, 2) ‘TF’: growth hormone (GH) transgenic salmon with ~ 3-fold higher growth-rate than W, 3) ‘TR’: GH transgenic fish ration restricted to possess a growth-rate equal to W, and 4) ‘D’: domesticated non-transgenic fish showing growth-rate intermediate to W and TF. D and TF showed a higher similarity in transcriptomic response compared to W and TR. Several immune genes showed constitutive expression differences among growth response groups, including perforin 1 and C-C motif chemokine 19-like. Among the affected immune pathways, most were up-regulated by Poly I:C and PGN. In response to PGN, the c-type lectin receptor signalling pathway responded uniquely in TF and TR. In response to stimulation with both immune mimics, TR responded more strongly than other groups. Further, group-specific pathway responses to PGN stimulation included NOD-like receptor signalling in W and platelet activation in TR. TF consistently showed the most attenuated immune response relative to W, and more DEGs were apparent in TR than TF and D relative to W, suggesting that a non-satiating ration coupled with elevated circulating GH levels may cause TR to possess enhanced immune capabilities. Alternatively, TF and D salmon are prevented from acquiring the same level of immune response as TR due to direction of energy to high overall somatic growth. Further study of the effects of ration restriction in growth-modified fishes is warranted. Conclusions These findings improve our understanding of the pleiotropic effects of growth modification on the immunological responses of fish, revealing unique immune pathway responses depending on the mechanism of growth acceleration and nutritional availability.

Recent evidence suggests that androgens are a potent driver of growth during late the primary stage of ovarian follicle development in teleosts. We have previously shown that the non-aromatizable androgen, 11-ketotestosterone (11-KT), both advances ovarian follicle growth in vivo and dramatically alters the primary growth ovarian transcriptome in coho salmon. Many of the transcriptomic changes pointed towards 11-KT driving process associated with the transition to a secondary growth phenotype. In the current study, we implanted previtellogenic early secondary growth coho salmon with cholesterol pellets containing 11-KT and performed RNA-Seq on ovarian tissue after 3 days in order to identify alterations to the ovarian transcriptome in early secondary growth. We identified 8,707 contiguous sequences (contigs) that were differentially expressed (DE) between control and 11-KT implanted fish and were able to collapse those to 3,853 gene-level IDs, more than a 3-fold more DE contigs than at the primary growth stage we reported previously. These contigs included genes encoding proteins involved in steroidogenesis, vitellogenin and lipid uptake, follicle stimulating hormone signaling, growth factor signaling, and structural proteins, suggesting androgens continue to promote previtellogenic secondary growth.

This study investigates the effect of dietary Lactobacillus plantarum supplementation on juvenile coho salmon (Oncorhynchus kisutch). Four groups of the juveniles (initial weight 103.87 ± 2.65 g) were fed for 10 weeks with four diets containing 0 (control diet), 105 (T1), 107 (T2), and 109 (T3) cfu/g of L. plantarum. The main results are as follows: Compared with the control diet, the final weight, specific growth rate (SGR), and weight gain rate (WGR) of the juveniles fed the T1, T2, and T3 diet significantly (p < 0.05) increased, while the feed coefficient ratio (FCR) expressed an opposite trend. The activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX) in the serum of the juveniles fed the T2 diet significantly (p < 0.05) increased, while the malondialdehyde (MDA) expressed an opposite trend. The expression of phosphatidylinositol 4,5-bisphosphate 3-kinase (pi3k), AKT-interacting protein (akt), mechanistic target of rapamycin kinase (mtor), glucose-6-phosphate dehydrogenase (g6pd), sod, cat, and gsh-px genes in the liver of the juveniles fed the T2 diet significantly (p < 0.05) increased. In conclusion, the T2 diet significantly improved the growth performance, antioxidant capacity, and upregulated key mTOR pathway genes in juvenile coho salmon.

5′adenosine monophosphate-activated protein kinase (AMPK) is a master regulator of energy homeostasis in eukaryotes. This study identified expansions in the AMPK-α, -β and -γ families of salmonid fishes due to a history of genome duplication events, including five novel salmonid-specific AMPK subunit gene paralogue pairs. We tested the hypothesis that the expanded AMPK gene system of salmonids is transcriptionally regulated by growth and immunological status. As a model, we studied immune-stimulated coho salmon ( Oncorhynchus kisutch ) from three experiment groups sharing the same genetic background, but showing highly-divergent growth rates and nutritional status. Specifically, we compared wild-type and GH-transgenic fish, the latter achieving either enhanced or wild-type growth rate via ration manipulation. Transcript levels for the fifteen unique salmonid AMPK subunit genes were quantified in skeletal muscle after stimulation with bacterial or viral mimics to alter immune status. These analyses revealed a constitutive up-regulation of several AMPK-α and -γ subunit-encoding genes in GH-transgenic fish achieving accelerated growth. Further, immune stimulation caused a decrease in the expression of several AMPK subunit-encoding genes in GH-transgenic fish specifically. The dynamic expression responses observed suggest a role for the AMPK system in balancing energetic investment into muscle growth according to immunological status in salmonid fishes.

Domestication has been extensively used in agricultural animals to modify phenotypes such as growth rate. More recently, transgenesis of growth factor genes [primarily growth hormone (GH)] has also been explored as a rapid approach to accelerating performance of agricultural species. Growth rates of many fishes respond dramatically to GH gene transgenesis, whereas genetic engineering of domestic mammalian livestock has resulted in relatively modest gains. The most dramatic effects of GH transgenesis in fish have been seen in relatively wild strains that have undergone little or no selection for enhanced growth, whereas genetic modification of livestock necessarily has been performed in highly domesticated strains that already possess very rapid growth. Such fast-growing domesticates may be refractory to further stimulation if the same regulatory pathways are being exploited by both genetic approaches. By directly comparing gene expression in wild-type, domestic, and GH transgenic strains of coho salmon, we have found that domestication and GH transgenesis are modifying similar genetic pathways. Genes in many different physiological pathways show modified expression in domestic and GH transgenic strains relative to wild-type, but effects are strongly correlated. Genes specifically involved in growth regulation (IGF1, GHR, IGF-II, THR) are also concordantly regulated in domestic and transgenic fish, and both strains show elevated levels of circulating IGF1. Muscle expression of GH in nontransgenic strains was found to be elevated in domesticated fish relative to wild type, providing a possible mechanism for growth enhancement. These data have implications for genetic improvement of existing domesticated species and risk assessment and regulation of emerging transgenic strains.

Estimating diet composition is important for understanding interactions between predators and prey and thus illuminating ecosystem function. The diet of many species, however, is difficult to observe directly. Genetic analysis of fecal material collected in the field is therefore a useful tool for gaining insight into wild animal diets. In this study, we used high-throughput DNA sequencing to quantitatively estimate the diet composition of an endangered population of wild killer whales (Orcinus orca) in their summer range in the Salish Sea. We combined 175 fecal samples collected between May and September from five years between 2006 and 2011 into 13 sample groups. Two known DNA composition control groups were also created. Each group was sequenced at a ~330bp segment of the 16s gene in the mitochondrial genome using an Illumina MiSeq sequencing system. After several quality controls steps, 4,987,107 individual sequences were aligned to a custom sequence database containing 19 potential fish prey species and the most likely species of each fecal-derived sequence was determined. Based on these alignments, salmonids made up >98.6% of the total sequences and thus of the inferred diet. Of the six salmonid species, Chinook salmon made up 79.5% of the sequences, followed by coho salmon (15%). Over all years, a clear pattern emerged with Chinook salmon dominating the estimated diet early in the summer, and coho salmon contributing an average of >40% of the diet in late summer. Sockeye salmon appeared to be occasionally important, at >18% in some sample groups. Non-salmonids were rarely observed. Our results are consistent with earlier results based on surface prey remains, and confirm the importance of Chinook salmon in this population's summer diet.

There are few reports examining the effects of simultaneous administration of multiple killed lactic acid bacteria with different physiological properties to fish. In this study, we fed three heat‐sterilized lactic acid bacteria, Lactobacillus delbrueckii (Lac‐b‐d), Leuconostoc mesenteroides (Leu‐m), and Lactococcus lactis (Lac‐c‐l), either singly or in combination (Combination), to juvenile coho salmon Oncorhynchus kisutch for 4 weeks and examined the changes in the physiological responses of the fish. At a daily bacterial intake of 0.1 mg/kg BW, granulocyte increased in the Leu‐m, Lac‐c‐l, and Combination groups; lymphocyte increased in the Lac‐c‐l group; and granulocyte phagocytic activity was higher in the Lac‐b‐d and Combination groups. In a 4‐week feeding experiment in which the intake of the multispecies Combination was varied, a feeding attraction effect was found in the 0.05 and 0.1 mg/kg BW/day groups, red blood cell and lymphocyte counts, granulocyte phagocytic activity, and potential killing activity were significantly higher in the combination group than in the control group. The survival rate in hypoxic conditions was also remarkably higher in the 0.05 and 0.1 mg/kg BW/day combination groups. These results suggest that the administration of multiple heat‐killed lactic acid bacteria is effective in improving the physiological responses of fish.

Sustainable aquaculture, which entails proportional replacement of fish-based feed sources by plant-based ingredients, is impeded by the poor growth response frequently seen in fish fed high levels of plant ingredients. This study explores the potential to improve, by means of early nutritional exposure, the growth of fish fed plant-based feed. Rainbow trout swim-up fry were fed for 3 weeks either a plant-based diet (diet V, V-fish) or a diet containing fishmeal and fish oil as protein and fat source (diet M, M-fish). After this 3-wk nutritional history period, all V- or M-fish received diet M for a 7-month intermediate growth phase. Both groups were then challenged by feeding diet V for 25 days during which voluntary feed intake, growth, and nutrient utilisation were monitored (V-challenge). Three isogenic rainbow trout lines were used for evaluating possible family effects. The results of the V-challenge showed a 42% higher growth rate (P = 0.002) and 30% higher feed intake (P = 0.005) in fish of nutritional history V compared to M (averaged over the three families). Besides the effects on feed intake, V-fish utilized diet V more efficiently than M-fish, as reflected by the on average 18% higher feed efficiency (P = 0.003). We noted a significant family effect for the above parameters (P<0.001), but the nutritional history effect was consistent for all three families (no interaction effect, P>0.05). In summary, our study shows that an early short-term exposure of rainbow trout fry to a plant-based diet improves acceptance and utilization of the same diet when given at later life stages. This positive response is encouraging as a potential strategy to improve the use of plant-based feed in fish, of interest in the field of fish farming and animal nutrition in general. Future work needs to determine the persistency of this positive early feeding effect and the underlying mechanisms.

A thorough reconstruction of historical processes is essential for a comprehensive understanding of the mechanisms shaping patterns of genetic diversity. Indeed, past and current conditions influencing effective population size have important evolutionary implications for the efficacy of selection, increased accumulation of deleterious mutations, and loss of adaptive potential. Here, we gather extensive genome-wide data that represent the extant diversity of the Coho salmon (Oncorhynchus kisutch) to address two objectives. We demonstrate that a single glacial refugium is the source of most of the present-day genetic diversity, with detectable inputs from a putative secondary micro-refugium. We found statistical support for a scenario whereby ancestral populations located south of the ice sheets expanded recently, swamping out most of the diversity from other putative micro-refugia. Demographic inferences revealed that genetic diversity was also affected by linked selection in large parts of the genome. Moreover, we demonstrate that the recent demographic history of this species generated regional differences in the load of deleterious mutations among populations, a finding that mirrors recent results from human populations and provides increased support for models of expansion load. We propose that insights from these historical inferences should be better integrated in conservation planning of wild organisms, which currently focuses largely on neutral genetic diversity and local adaptation, with the role of potentially maladaptive variation being generally ignored.