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Copyright of Journal of Hydrobiology is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A twelve-week feeding experiment was undertaken to explore the impact of substituting dietary fish meal (FM) and fish oil (FO) with complex protein (CP) and canola oil (CO) in the diet of triploid rainbow trout on the quality of their fillets. The control diet (F100) contained FM (60%) and FO (18.6%) as the main protein and lipid sources. Based on this, 50% and 100% of FM and FO were substituted by CP and CO and they were named as F50 and F0, respectively. The results showed that there were no significant differences in the specific growth rates, condition factors, gutted yields, fillet yields and yellowness values as the substitution levels increased (p > 0.05). The F50 treatment obtained the highest values of fillet springiness and chewiness, improved the umami and bitter taste of the fillets by increasing the contents of inosine-5′-monophosphate and histidine, and increased lipid, protein, C18: 1n-9 and C18: 2n-6 contents (p < 0.05). The F0 treatment obtained the highest values of fillet hardness and pH, attenuated the sweet taste of the fillets by decreasing the content of glycine, and decreased the contents of EPA and DHA (p < 0.05). Both F50 and F0 treatments could increase the redness value, decrease the lightness and hue values of fillets, and increase the odor intensity, resulting in the typical fillet odors of green, fatty, orange and fishy (p < 0.05). In general, 50% and 100% of FM and FO substitution did not affect the growth of trout, but it did affect quality. Compared to the F100 treatment, the fillet quality of the F0 treatment was similar to the F50 treatment and could improve the appearance and odor intensity of the fillets. However, the difference was that the F50 treatment increased the springiness, umami, bitterness and lipid nutritional value of the fillets, but the F0 treatment increased the hardness, decreased the sweetness, and decreased the lipid, EPA and DHA contents of the fillets. [ABSTRACT FROM AUTHOR]

This study evaluates the effects of dietary Clostridium butyricum on growth performance and intestinal health in triploid rainbow trout (Oncorhynchus mykiss). Administered in a 12-week trial, five isonitrogenous and isolipidic feeds contained different C. butyricum levels [G1 (0), G2 (1.6 × 106 CFU/g), G3 (1.2 × 107 CFU/g), G4 (1.1 × 108 CFU/g), and G5 (1.3 × 109 CFU/g)]. Significant enhancements in growth performance, including improved feed conversion ratios and specific growth rates in the G4 group, were indicative of enhanced nutrient utilization, corroborated by optimal digestive enzyme activity levels. Antioxidant capabilities were also enhanced in the G4 group, indicated by increased serum superoxide dismutase and catalase activities, along with a significant decrease in malondialdehyde levels. Gut microbiota analysis indicated a probiotic concentration-dependent modulation of microbial communities, with a marked enrichment in beneficial bacterial phyla like Firmicutes in the G4 group. This microbial shift correlated with significant downregulations in immune-related gene expressions, including interleukins (IL-1β, IL-8), NF-κB, MyD88, and TNF-α, highlighting an activated immune response. Correspondingly, serum lysozyme and immunoglobulin M contents were significantly elevated in the G4 group. Challenge tests with Aeromonas salmonicida exhibited the higher disease resistance of fish fed the G4 diet. In conclusion, the study shows the potential of dietary C. butyricum, especially at 1.1 × 108 CFU/g, in enhancing the growth, health, and disease resistance of triploid rainbow trout through modulating gut microflora and stimulating immune responses. [ABSTRACT FROM AUTHOR]

Triploid rainbow trout is a hypoxia-sensitive fish species, and is susceptible to death in summer with high water temperature induced acute hypoxia. The study was conducted to evaluate the effect of high protein diet and high carbohydrate diet on hypoxic tolerance of triploid rainbow trout. Two isolipidic and isoenergetic diets with low protein-high carbohydrate level (LPHC) and high protein-low carbohydrate level (HPLC) were specifically formulated. After the feeding trial with 80 days, two group fish were treated with acute hypoxic challenge. Plasma biochemical parameters, hepatic anti-stress, antioxidant and immune related genes expression, and hepatic glucose, lipid, protein and amino acid metabolism related genes expression were then analyzed. The results showed that compared with HPLC diet, LPHC diet could result in excessive plasma levels of alanine aminotransferase (ALT; 36.3 VS 14.0 U/L), aspartate aminotransferase (AST; 978 VS 366 U/L), alkaline phosphatase (ALP; 374 VS 204 U/L), creatine phosphokinase (CPK; 7538 VS 4937 U/L) and lactate dehydrogenase (LDH; 940 VS 451 U/L). In addition, HPLC diet could remodel metabolism of glucose, lipid and protein based on the mRNA expression levels of the genes regulating glycometabolism, lipometabolism, and protein and amino acids metabolism. HPLC diet also enhanced the mRNA expression levels of the genes regulating anti-stress (HSP70, HIF-1a and HIF-2a), antioxidant (Nrf2, SOD, CAT, GPx and HO-1) and immune (IFN-γ, IL-1β, TNF-α and IL-8). In total, LPHC diet could aggravate hypoxic stress of triploid rainbow trout, while HPLC diet could improve fish hypoxic tolerance.

[Objective] This study obtained the complete mitochondrial genome sequence (mtDNA) of triploid rainbow trout, revealed key sequence structural features, explored phylogenetic information of triploid rainbow trout and enriched the mtDNA database of salmonid fishes to provide references for evolutionary and phylogenetic studies of triply distributed rainbow trout. [Method] Three healthy and similar-sized triploid rainbow trout were selected, and their upper dorsal spinal muscular tissue was harvested for ge-nomic DNA extraction. The triploid rainbow trout mtDNA was sequenced, assembled and annotated by 11-lumina sequencing technology after quality control of DNA, followed by bioinformatic analysis. Neighbour-Joining (NJ) was used to build a phylogenetic salmonid fish tree. [Result] The mtDNA of triploid rainbow trout was 16 655 bp in length with high A + T (54.06%) and low G + C (45.94%). Its base composition had a clear A/T bias. The triploid rainbow trout mtDNA was composed of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and 1 noncoding control region (D-loop region). Among the 13 protein-coding genes, 1 2 had an ATG start codon and a TNN stop codon, except for coxl, which had a GTG start one. The total length of the 2 rRNA genes was 2 606 bp and 21 out of 22 tRNA genes except trnSl were able to form a typical trilobal structure. The D-loop region was located between trnF and trnP in the circular DNA molecule. The results of the phylogenetic tree showed that the 28 species were clearly divided into two large clades, with species of Oncorhynchus, Parahucho, Brachymystax, Phyllostomus, Hucho, Salvelinus and Salmo in the Salmonidae clustered into one clade. The triploid rainbow trout and Oncorhynchus mykiss firstly clustered into one clade, indicating their closest kinship. The genus species in the Thymallinae Thymallus and Coregonus and Prosopium species in the Coregoninae clustered into another clade. [Conclusion] mtDNA of triploid rainbow trout was obtained, and triploid rainbow trout and Oncorhynchus mykiss were most closely related. [ABSTRACT FROM AUTHOR]

Diploid rainbow trout gonadal development occurs at the expense of stored energy and nutrients, lipid mobilization supplies energy required for this process. However, triploid rainbow trout gonads are not developed, the lipid and fatty acid metabolism might be different. However, which metabolic pathways and key metabolites regulate fatty acid metabolism have not been clarified. To identify the metabolism difference between diploid and triploid rainbow trout, we use the LC-MS technology based metabolomics to detect the metabolites in positive and negative ion mode. As far as it was evaluated, there are 174 metabolites with statistically significant differences, including 13 lipids and lipid-like molecules. Among the different metabolites, linoleic acid (LA), oleic acid (OA) and arachidonic acid (ARA) were related to the biosynthesis of unsaturated fatty acids, LA and OA were related to linoleic acid metabolism. The two metabolic pathways related to Polyunsaturated fatty acid (PUFA) metabolism might be associated with the differences in PUFA contents in diploid and triploid rainbow trout serum. Gene expression results validated that and pointed that the desaturation process maybe more crucial process in the differential metabolic pathways between diploid and triploid rainbow trout. The study provide a theoretical explanation for PUFA metabolism differences between diploid and triploid rainbow trout, identify the crucial metabolites as biomarkers to differentiate the metabolic mechanisms of PUFA metabolism in rainbow trout.

Abstract Background Rainbow trout (Oncorhynchus mykiss) is becoming popular with the increased demand for fish protein. However, the limited resources and expense of fish meal and oil have become restrictive factors for the development of the rainbow trout related industry. To solve this problem, plant-derived proteins and vegetable oils have been developed as alternative resources. The present study focuses on evaluating the effects of two experimental diets, FMR (fish meal replaced with plant-derived protein) and FOR (fish oil replaced with rapeseed oil), through the alteration of the gut microbiota in triploid rainbow trout. The commercial diet was used in the control group (FOM). Results Amplicon sequencing of the 16S and 18S rRNA genes was used to assess the changes in gut bacteria and fungi. Our analysis suggested that the α-diversity of both bacteria and fungi decreased significantly in the FMR and FOR groups, and β-diversity was distinct between FOM/FMR and FOM/FOR based on principal coordinate analysis (PCoA). The abundance of the Planctomycetota phylum increased significantly in the FMR group, while that of Firmicutes and Bacteroidetes decreased. We also found that the fungal phylum Ascomycota was significantly increased in the FMR and FOR groups. At the genus level, we found that the abundance of Citrobacter was the lowest and that of pathogenic Schlesneria, Brevundimonas, and Mycoplasma was highest in the FMR and FOR groups. Meanwhile, the pathogenic fungal genera Verticillium and Aspergillus were highest in the FMR and FOR groups. Furthermore, canonical correspondence analysis (CCA) and network analysis suggested that the relatively low-abundance genera, including the beneficial bacteria Methylobacterium, Enterococcus, Clostridium, Exiguobacterium, Sphingomonas and Bacteroides and the fungi Papiliotrema, Preussia, and Stachybotrys, were positively correlated with plant protein or rapeseed oil. There were more modules that had the above beneficial genera as the hub nodes in the FMR and FOR groups. Conclusions Our study suggested that the FMR and FOR diets could affect the gut microbiome in rainbow trout, which might offset the effects of the dominant and pathogenic microbial genera. This could be the underlying mechanism of explaining why no significant difference was observed in body weight between the different groups.

Background: Rainbow trout (Oncorhynchus mykiss) is becoming popular with the increased demand for fish protein. However, the limited resources and expense of fish meal and oil have become restrictive factors for the development of the rainbow trout related industry. To solve this problem, plant-derived proteins and vegetable oils have been developed as alternative resources. The present study focuses on evaluating the effects of two experimental diets, FMR (fish meal replaced with plant-derived protein) and FOR (fish oil replaced with rapeseed oil), through the alteration of the gut microbiota in triploid rainbow trout. The commercial diet was used in the control group (FOM). Results: Amplicon sequencing of the 16S and 18S rRNA genes was used to assess the changes in gut bacteria and fungi. Our analysis suggested that the α-diversity of both bacteria and fungi decreased significantly in the FMR and FOR groups, and β-diversity was distinct between FOM/FMR and FOM/FOR based on principal coordinate analysis (PCoA). The abundance of the Planctomycetota phylum increased significantly in the FMR group, while that of Firmicutes and Bacteroidetes decreased. We also found that the fungal phylum Ascomycota was significantly increased in the FMR and FOR groups. At the genus level, we found that the abundance of Citrobacter was the lowest and that of pathogenic Schlesneria, Brevundimonas, and Mycoplasma was highest in the FMR and FOR groups. Meanwhile, the pathogenic fungal genera Verticillium and Aspergillus were highest in the FMR and FOR groups. Furthermore, canonical correspondence analysis (CCA) and network analysis suggested that the relatively low-abundance genera, including the beneficial bacteria Methylobacterium, Enterococcus, Clostridium, Exiguobacterium, Sphingomonas and Bacteroides and the fungi Papiliotrema, Preussia, and Stachybotrys, were positively correlated with plant protein or rapeseed oil. There were more modules that had the above beneficial genera as the hub nodes in the FMR and FOR groups. Conclusions: Our study suggested that the FMR and FOR diets could affect the gut microbiome in rainbow trout, which might offset the effects of the dominant and pathogenic microbial genera. This could be the underlying mechanism of explaining why no significant difference was observed in body weight between the different groups. [ABSTRACT FROM AUTHOR]

A twelve-week feeding experiment was undertaken to explore the impact of substituting dietary fish meal (FM) and fish oil (FO) with complex protein (CP) and canola oil (CO) in the diet of triploid rainbow trout on the quality of their fillets. The control diet (F100) contained FM (60%) and FO (18.6%) as the main protein and lipid sources. Based on this, 50% and 100% of FM and FO were substituted by CP and CO and they were named as F50 and F0, respectively. The results showed that there were no significant differences in the specific growth rates, condition factors, gutted yields, fillet yields and yellowness values as the substitution levels increased (p > 0.05). The F50 treatment obtained the highest values of fillet springiness and chewiness, improved the umami and bitter taste of the fillets by increasing the contents of inosine-5′-monophosphate and histidine, and increased lipid, protein, C18: 1n-9 and C18: 2n-6 contents (p < 0.05). The F0 treatment obtained the highest values of fillet hardness and pH, attenuated the sweet taste of the fillets by decreasing the content of glycine, and decreased the contents of EPA and DHA (p < 0.05). Both F50 and F0 treatments could increase the redness value, decrease the lightness and hue values of fillets, and increase the odor intensity, resulting in the typical fillet odors of green, fatty, orange and fishy (p < 0.05). In general, 50% and 100% of FM and FO substitution did not affect the growth of trout, but it did affect quality. Compared to the F100 treatment, the fillet quality of the F0 treatment was similar to the F50 treatment and could improve the appearance and odor intensity of the fillets. However, the difference was that the F50 treatment increased the springiness, umami, bitterness and lipid nutritional value of the fillets, but the F0 treatment increased the hardness, decreased the sweetness, and decreased the lipid, EPA and DHA contents of the fillets.

This study evaluates the effects of dietary Clostridium butyricum on growth performance and intestinal health in triploid rainbow trout (Oncorhynchus mykiss). Administered in a 12-week trial, five isonitrogenous and isolipidic feeds contained different C. butyricum levels [G1 (0), G2 (1.6 × 106 CFU/g), G3 (1.2 × 107 CFU/g), G4 (1.1 × 108 CFU/g), and G5 (1.3 × 109 CFU/g)]. Significant enhancements in growth performance, including improved feed conversion ratios and specific growth rates in the G4 group, were indicative of enhanced nutrient utilization, corroborated by optimal digestive enzyme activity levels. Antioxidant capabilities were also enhanced in the G4 group, indicated by increased serum superoxide dismutase and catalase activities, along with a significant decrease in malondialdehyde levels. Gut microbiota analysis indicated a probiotic concentration-dependent modulation of microbial communities, with a marked enrichment in beneficial bacterial phyla like Firmicutes in the G4 group. This microbial shift correlated with significant downregulations in immune-related gene expressions, including interleukins (IL-1β, IL-8), NF-κB, MyD88, and TNF-α, highlighting an activated immune response. Correspondingly, serum lysozyme and immunoglobulin M contents were significantly elevated in the G4 group. Challenge tests with Aeromonas salmonicida exhibited the higher disease resistance of fish fed the G4 diet. In conclusion, the study shows the potential of dietary C. butyricum, especially at 1.1 × 108 CFU/g, in enhancing the growth, health, and disease resistance of triploid rainbow trout through modulating gut microflora and stimulating immune responses.

To investigate the flavor profile of triploid rainbow trout from Qinghai Province, high performance liquid chromatography (HPLC) and headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) were used to analyze the flavor compounds of fish cultured in net cages from Longyangxia, Gongboxia and Laxiwa. Results showed that the inosinic acid (IMP) content of farmed rainbow trout in Qinghai Province was 176~242 mg/100 g. The IMP content of rainbow trout in Gongboxia and Laxiwa was significantly higher than that in Longyangxia group (P

Copyright of Journal of Hydrobiology is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Smolting is an important development stage of salmonid, and an energy trade-off occurs between osmotic regulation and growth during smolting in rainbow trout (Oncorhynchus mykiss). Growth hormone releasing hormone, somatostatin, growth hormone and insulin-like growth factor (GHRH-SST-GH-IGF) axis exhibit pleiotropic effects in regulating growth and osmotic adaptation. Due to salmonid specific genome duplication, increased paralogs are identified in the ghrh-sst-gh-igf axis, however, their physiology in modulating osmoregulation has yet to be investigated. In this study, seven sst genes (sst1a, sst1b, sst2, sst3a, sst3b, sst5, sst6) were identified in trout. We further investigated the ghrh-sst-gh-igf axis of diploid and triploid trout in response to seawater challenge. Kidney sst (sst1b, sst2, sst5) and sstr (sstr1b1, sstr5a, sstr5b) expressions were changed (more than 2-fold increase (except for sstr5a with 1.99-fold increase) or less than 0.5-fold decrease) due to osmoregulation, suggesting a pleiotropic physiology of SSTs in modulating growth and smoltification. Triploid trout showed significantly down-regulated brain sstr1b1 and igfbp2a1 (p < 0.05), while diploid trout showed up-regulated brain igfbp1a1 (~2.61-fold, p = 0.057) and igfbp2a subtypes (~1.38-fold, p < 0.05), suggesting triploid trout exhibited a better acclimation to the seawater environment. The triploid trout showed up-regulated kidney igfbp5a subtypes (~6.62 and 7.25-fold, p = 0.099 and 0.078) and significantly down-regulated igfbp5b2 (~0.37-fold, p < 0.05), showing a conserved physiology of teleost IGFBP5a in regulating osmoregulation. The IGFBP6 subtypes are involved in energy and nutritional regulation. Distinctive igfbp6 subtypes patterns (p < 0.05) potentially indicated trout triggered energy redistribution in brain and kidney during osmoregulatory regulation. In conclusion, we showed that the GHRH-SST-GH-IGF axis exhibited pleiotropic effects in regulating growth and osmoregulatory regulation during trout smolting, which might provide new insights into seawater aquaculture of salmonid species. [ABSTRACT FROM AUTHOR]

This experiment simulated the hypoxic environment caused by actual production operations in fish farming (i.e., catching, gathering, transferring, and weighting) to study the effects of acute hypoxic conditions on the physiological and metabolic responses of triploid rainbow trout (O. mykiss). Two groups of fish weighting 590 g were sampled in the normoxia group (dissolved oxygen above 7 mg/L) and hypoxia group (dissolved oxygen ranged from 2 to 5 mg/L for 10 min). The results showed that 1) regarding stress response, hypoxia increased plasma levels of cortisol, heat shock protein 70 (HSP-70), lysozyme, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and creatine phosphokinase (CPK); induced the expression of hepatic genes encoding nuclear factor erythroid 2 related factor 2 (Nrf2), interferon γ (IFN-γ) and interleukin-1β (IL-1β). 2) Regarding metabolism response, hypoxia increased plasma levels of globulin (GLOB), glucose (GLU), triglyceride (TG) and lactate dehydrogenase (LDH); upregulated the hepatic gene expression of phosphoenolpyruvate carboxykinase, (PEPCK), pyruvate dehydrogenase kinase (PDK1), acetyl-CoA carboxylase (ACC) and acetyl-CoA oxidase (ACO); downregulated the hepatic gene expression of carnitine palmitoyl transferase 1 (CPT1); and unchanged the expression of hepatic genes in glycolysis and autophagy. 3) In response to hypoxia-inducible factors (HIFs), the hepatic HIF-2α gene was activated in the hypoxia group, but HIF-1α gene expression remained unchanged. Thus, during acute hypoxic stress, triploid rainbow trout were in a defensive state, with an enhanced immune response and altered antioxidant status. Additionally, the hepatic mitochondrial oxidation of glucose- and lipid-derived carbon in trout was suppressed, and hepatic gluconeogenesis and lipid synthesis were activated, which might be regulated by the HIF-2α pathway. [ABSTRACT FROM AUTHOR]

Selenium(Se) is a biological essential trace element that affects the growth and health of fish. The present study aimed to explore the dietary Se requirement of triploid rainbow trout using Se-yeast supplement. The levels of Se added to the basal diet were 0(Se0), 0.1(Se0.1), 0.3(Se0.3), 0.5(Se0.5), 1.0(Se1.0), 4.0(Se4.0) and 16.0(Se16.0) mg Se/kg diet respectively. Results showed that the fish fed Se4.0 diet had significantly higher weight gain and lower oxidative stress compared with the fish fed Se16.0 and Se0 diets. The optimal dietary Se requirement of triploid rainbow trout was 3.53 mg/kg based on broken-line regression of growth performance. Dietary Se supplementation significantly increased the expression level of selenoprotein genes both in liver (GPX1a, GPX1b1, GPX1b2, SelK, SelP, SelT1, SelT2, SelWl, TrxR3a, SelU) and in muscle (GPX1a, GPX1b2, SelK, SelP, SelU, SelWl, TrxR3b, SelN, MsrB1Al). The minimum dietary Se level was 2.19 or 1.28 mg/kg when the mRNA level of all these selenoproteins reached a plateau in muscle or liver respectively. In conclusion, based on broken-line regression of growth performance and sigmoidal regression of selenoprotein genes expression in muscle and liver, dietary Se requirement of triploid rainbow trout was 3.53, 2.19 and 1.28 mg/kg respectively. [ABSTRACT FROM AUTHOR]

The impacts of global warming are widespread and profound, prolonged temperature increases can pose a serious threat to various organisms. Knowing the process underlying fish tolerance to high water temperature can develop practical solutions for fish to adapt to climate change. As a typical cold-water cultured fish, rainbow trout (Oncorhynchus mykiss) is an ideal model for studying thermal stress response strategies in cold-water fish in the context of global warming. In this study, we methodically inspected how extended high-water temperature affected the growth performance, feed utilization, blood biochemical indexes, morphological observation of liver, intestinal and gill tissues, as well as related enzyme activities and gene mRNA expression of triploid rainbow trout. Thus, two groups (three replicates) were designed: the chronic heat stress group (HG, 19.21 ± 0.05 °C) and the control group (CG, 15.13 ± 0.07 °C), each group contained 45 fish and feeding trial with 31 days. A decline in growth performance, including the final weight, weight gain rate, and feed intake, was observed in the HG during the current investigation. In response to prolonged heat stress, the level of plasma cortisol, aspartate aminotransferase, alanine aminotransferase and heat shock protein 70 (HSP70) increased. Our results also showed there were fewer glycogen particles in the liver after chronic heat stress. Interestingly, an increase in the enzyme activity of glucose metabolism but not lipid metabolism was observed in the HG. Chronic heat stress caused the intestine's digestive enzyme activity (lipase, protease, and amylase) to decrease while goblet cell counts dramatically rose. Additionally, gill morphology underwent remodeling under chronic heat stress, including modification in the distance between interlamellar, secondary lamellar length and basal epithelial thickness. Meanwhile, higher levels of gene expression linked to autophagy and apoptosis were detected in gills. The above results indicate that under chronic heat stress, triploid rainbow trout responded to heat stress by accelerating hepatic glycogenolysis, resisting intestinal inflammation, and remodeling gill structure to ensure that the fish could survive for a long time. However, this acclimatization process leads to a decrease in intestinal digestibility, resulting in a decrease in the growth performance of triploid rainbow trout. In summary, the changes in growth performance, organ morphology, physiological, biochemical and metabolic changes reveal special heat stress adaptations in triploid rainbow trout under chronic heat stress. • Chronic heat stress does not affect the survival of triploid rainbow trout but reduces growth performance. • Significant changes in hepatic glucose metabolism were observed in triploid rainbow trout after chronic heat stress. • Gills of triploid rainbow trout adapt to chronic heat stress through morphological remodeling • Enhanced anti-inflammatory activity and antioxidant capacity of triploid rainbow trout intestine during chronic heat stress • The study elucidated the mechanisms of adaptation to chronic heat stress in triploid rainbow trout [ABSTRACT FROM AUTHOR]

This experiment simulated the hypoxic environment caused by actual production operations in fish farming (i.e., catching, gathering, transferring, and weighting) to study the effects of acute hypoxic conditions on the physiological and metabolic responses of triploid rainbow trout (O. mykiss). Two groups of fish weighting 590 g were sampled in the normoxia group (dissolved oxygen above 7 mg/L) and hypoxia group (dissolved oxygen ranged from 2 to 5 mg/L for 10 min). The results showed that 1) regarding stress response, hypoxia increased plasma levels of cortisol, heat shock protein 70 (HSP-70), lysozyme, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and creatine phosphokinase (CPK); induced the expression of hepatic genes encoding nuclear factor erythroid 2 related factor 2 (Nrf2), interferon γ (IFN-γ) and interleukin-1β (IL-1β). 2) Regarding metabolism response, hypoxia increased plasma levels of globulin (GLOB), glucose (GLU), triglyceride (TG) and lactate dehydrogenase (LDH); upregulated the hepatic gene expression of phosphoenolpyruvate carboxykinase, (PEPCK), pyruvate dehydrogenase kinase (PDK1), acetyl-CoA carboxylase (ACC) and acetyl-CoA oxidase (ACO); downregulated the hepatic gene expression of carnitine palmitoyl transferase 1 (CPT1); and unchanged the expression of hepatic genes in glycolysis and autophagy. 3) In response to hypoxia-inducible factors (HIFs), the hepatic HIF-2α gene was activated in the hypoxia group, but HIF-1α gene expression remained unchanged. Thus, during acute hypoxic stress, triploid rainbow trout were in a defensive state, with an enhanced immune response and altered antioxidant status. Additionally, the hepatic mitochondrial oxidation of glucose- and lipid-derived carbon in trout was suppressed, and hepatic gluconeogenesis and lipid synthesis were activated, which might be regulated by the HIF-2α pathway.

Smolting is an important development stage of salmonid, and an energy trade-off occurs between osmotic regulation and growth during smolting in rainbow trout (Oncorhynchus mykiss). Growth hormone releasing hormone, somatostatin, growth hormone and insulin-like growth factor (GHRH-SST-GH-IGF) axis exhibit pleiotropic effects in regulating growth and osmotic adaptation. Due to salmonid specific genome duplication, increased paralogs are identified in the ghrh-sst-gh-igf axis, however, their physiology in modulating osmoregulation has yet to be investigated. In this study, seven sst genes (sst1a, sst1b, sst2, sst3a, sst3b, sst5, sst6) were identified in trout. We further investigated the ghrh-sst-gh-igf axis of diploid and triploid trout in response to seawater challenge. Kidney sst (sst1b, sst2, sst5) and sstr (sstr1b1, sstr5a, sstr5b) expressions were changed (more than 2-fold increase (except for sstr5a with 1.99-fold increase) or less than 0.5-fold decrease) due to osmoregulation, suggesting a pleiotropic physiology of SSTs in modulating growth and smoltification. Triploid trout showed significantly down-regulated brain sstr1b1 and igfbp2a1 (p < 0.05), while diploid trout showed up-regulated brain igfbp1a1 (~2.61-fold, p = 0.057) and igfbp2a subtypes (~1.38-fold, p < 0.05), suggesting triploid trout exhibited a better acclimation to the seawater environment. The triploid trout showed up-regulated kidney igfbp5a subtypes (~6.62 and 7.25-fold, p = 0.099 and 0.078) and significantly down-regulated igfbp5b2 (~0.37-fold, p < 0.05), showing a conserved physiology of teleost IGFBP5a in regulating osmoregulation. The IGFBP6 subtypes are involved in energy and nutritional regulation. Distinctive igfbp6 subtypes patterns (p < 0.05) potentially indicated trout triggered energy redistribution in brain and kidney during osmoregulatory regulation. In conclusion, we showed that the GHRH-SST-GH-IGF axis exhibited pleiotropic effects in regulating growth and osmoregulatory regulation during trout smolting, which might provide new insights into seawater aquaculture of salmonid species.

The present study identified the volatile compounds profile in raw muscle of triploid rainbow trout with different marketable sizes (eviscerated weight: 2 kg, 3 kg and 4 kg, respectively). Six fish per each size treatment were sampled in a local commercial trout farm, then raw muscles of sampled fish were filleted to detect the volatile compounds by using the gas chromatography-mass spectrometry (GCMS) analysis coupled with automated solid-phase microextraction (SPME) system. Results showed that a total of 58 volatile compounds were identified in raw muscle of triploid rainbow trout, including aldehydes (20 species), ketones (6 species), alcohols (9 species), hydrocarbons (11 species), aromatics (6 species) and miscellaneous compounds groups (6 species). The subtotal estimated concentration of aldehydes group was significantly higher than those of the other volatile groups (P 0.05). Based on the principle component analysis and cluster analysis using the odor activity values of 21 odor-active compounds, the overall odors of raw muscle might be similar in triploid rainbow trout with different marketable sizes.

To provide basic research data for the processing and comprehensive utilization of triploid rainbow trout, we studied the nutritional quality of muscle and skin tissue of different sizes of fish (1250.10 ± 1.22 g, 2555.31 ± 1.32 g, and 3823.10 ± 1.44 g). The results showed that the proportion of skin and muscle was the highest when fish body size was 2555.31 ± 1.32 g. In muscle, lysine content was the highest and methionine content was the lowest among the essential amino acids (EAAs). Glutamic acid content was the highest and glycine content was the lowest among all umami-related amino acids. With increasing size, EAA, D -aspartic acid (DAA), and total amino acid (TAA) levels first increased and then decreased. The Met + Cys group contained the most restricted amino acids in the skin and muscle, and 2555.31 ± 1.32 g triploid rainbow trout had better amino acid balance and the best nutritional value. Of the essential minerals, Na, Mg, and K were the most abundant. According to Dietary Reference Intakes (DRI), Mg, Fe, and Zn can provide higher nutritional quality. Finally, the results showed that nutritional quality was highest in the muscle of the intermediate-sized triploid rainbow trout. • Medium-sized Oncorhynchus mykiss had the most suitable for additional processing and utilization. • Protein, fat, ash and collagen content were highest in the muscle of intermediate-sized Oncorhynchus mykiss. • Among the essential and umami amino acids, lysine and glutamic acid was the highest content respectively. • The first limiting amino acid in both muscle and skin was Met+Cys. • The contents of Na, Mg and K were measured as the top three in both tissues. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to evaluate the effects of body size and seasonal variation on organ indexes, digestive enzymes and plasma biochemistry parameters of triploid rainbow trout. Results in experiment 1 showed that compared with small fish, large fish had significantly (P < 0.05) higher values of organ indexes, higher plasma nutrient contents as well as higher specific activities of lipase in pyloric caeca and amylase in the intestine. Results in experiment 2 showed that fish in spring or winter had greater intestine length as well as lower specific activities of protease and lipase in pyloric caeca (P < 0.05). Fish in autumn had the highest specific activities of acid protease in the stomach and alkaline protease in pyloric caeca, lipase in pyloric caeca as well as nutrient contents in plasma, while fish in summer had the lowest liver and viscera weight as well as plasma nutrient contents. Based on data of organ indexes, digestive enzymes and plasma biochemistry parameters, the physiological status of triploid rainbow trout were affected by fish size and seasonal variation. Normal reference ranges of organ indexes and plasma biochemical parameters of triploid rainbow trout were preliminarily established, which are partly different from diploid trout. [ABSTRACT FROM AUTHOR]

An 80-day feeding trial was conducted to assess the dietary protein requirement of sub-adult triploid rainbow trout (initial average weight: 233 g). Six isolipidic and isoenergetic diets were formulated to contain increasing levels of protein (31.6, 35.4, 40.7, 43.3, 45.8 and 52.4%). Each diet was fed to quadruplicate groups of fish (100 fish per group) in freshwater cages. Results showed that weight gain rate (WGR), protein gain, whole-body protein content, trypsin and chymotrypsin specific activities in intestine significantly (P < 0.05) increased with increasing dietary protein level and then plateaued (P > 0.05). Protein retention, protein efficiency ratio (PER), lipase in pyloric caeca and amylase specific activities significantly (P < 0.05) decreased with increasing dietary protein level. Fish fed the diet with 45.8% protein had higher feed efficiency (FE) and higher enteric peptide transporter 1 (Pep T1) gene expression level. Generally, fish fed diets with low dietary protein levels had lower feed intake (FI), higher hepatosomatic index (HSI), higher plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, higher hepatic glutamate dehydrogenase (GDH) activity, as well as higher malondialdehyde (MDA) contents in plasma, liver and intestine and lower total anti-oxidative capacity (T-AOC) contents in plasma and intestine (P < 0.05). Based on WGR, the optimum dietary protein requirement of sub-adult triploid rainbow trout was 45.8% dry matter with a diet containing 20% lipid and 22 kJ gross energy/g. This optimal dietary protein level improved the digestive and absorptive abilities of rainbow trout. Diets with lower protein levels (31.6–35.4%) led to increase lipid peroxidation level in whole fish body, while the diet with excess protein (52.4%) appeared to limit enteric Pep T1 gene expression level. • The optimum dietary protein requirement of sub-adult triploid rainbow trout was 45.8% dry matter with a diet containing 20% lipid. • Optimal dietary protein level improved the digestive and absorptive abilities of protein. • Diets with low protein levels (31.6-35.4%) led to increase lipid peroxidation level in whole fish body. • Diet with excess protein (52.4%) appeared to limit enteric peptide transporter 1 gene expression level. [ABSTRACT FROM AUTHOR]

The aim of the present study was to identify differences in the proximate composition, amino acid composition and expression of the muscle growth-related genes myogenic determining factor (MyoD) and myostatin (MSTN) in muscle between diploid and triploid female rainbow trout (Oncorhynchus mykiss) that were reared under the same conditions. The research included two different ages (12- and 16-month) of diploid and triploid rainbow trout. The lipid and protein contents of the triploid fish were significantly higher while their moisture content was significantly lower than those of the diploid fish. The amino acid compositions of the proteins of both diploid and triploid rainbow trout were well balanced. The percentages of total amino acids (WTAA), essential amino acids (WEAA), non-essential amino acids (WNEAA) and delicious amino acids were similar between the triploid and diploid fish. The WEAA to WTAA and WEAA to WNEAA indices were comparable to the reference values of nearly 40% and above 60%, respectively, recommended by the FAO/WHO. According to the amino acid scores, phenylalanine can be described as the first limiting amino acid, and the sum of methionine and cysteine represented the highest protein score in both diploid and triploid rainbow trout. MyoD1 mRNA expression was higher in triploid fish, while MSTN2 mRNA expression was higher in diploid fish. The growth potential was greater in triploid fish than in diploid fish. This study shows that both diploid and triploid rainbow trout are good protein sources; triploid rainbow trout is under further investigation due to presenting higher, balanced nutritional quality and better growth than the diploid fish. [ABSTRACT FROM AUTHOR]

A 12-week feeding trial was conducted to evaluate the impacts of high levels of canola oil (CO) substitution for fish oil (FO) on the growth and fillet quality of triploid rainbow trout. Three isonitrogenous (46% crude protein) and isolipidic (24% crude lipids) diets were prepared. The control diet containing supplemental FO with 18.6% level was compared with the diets, in which 75% (CO75) and 100% (CO100) FO was replaced by CO, respectively. Each diet was fed to quadruplicate groups of 100 fish (initial average weight of 208 g) in freshwater cages. Results showed that CO substitution did not significantly affect survival, weight gain rate and feed conversion ratio (P > 0.05), while affected fillet organoleptic properties and nutritional value based on the multivariate statistical analysis of 124 quality indicators. Generally, high levels of CO substitution significantly increased fillet redness (a ⁎ , C ⁎ ab), relative fillet length and fillet thickness value, fillet springiness and chewiness values, fillet collagen content and crosslink level, fillet odor-active compounds concentrations, fillet inosine-5′-monophosphate (IMP), glutamic acid, histidine, sum of bitter taste compounds and sum of sour taste compounds contents, and fillet lipid and total fatty acids contents (P < 0.05). However, total substitution of FO by CO could result in high fillet fragility and low n-3 long-chain polyunsaturated fatty acids (LC-PUFA) content. In total, CO substitution did not affect growth, and could increase fillet appearance, texture, umami quality and lipid nutritional value of triploid rainbow trout, while total CO substitution was not recommended. • High levels of canola oil (CO) substitution for fish oil (≥75%) did not negatively affect trout growth. • CO substitution could improve fillet color, texture, umami and lipid nutritional value. • CO substitution could increase fillet odor intensity, bitterness and sourness. • Total CO substitution could increase fillet fragility and decrease n-3 LC-PUFA content. [ABSTRACT FROM AUTHOR]

A growth trial was conducted to evaluate the effects of dietary lipid levels on the growth performance, feed utilization, digestive ability, health status and expression of growth-related genes of female triploid rainbow trout (Oncorhynchus mykiss). Six isonitrogenous diets, containing 46% protein were formulated with graded lipid levels of 6.6 (Diet 1), 12.3 (Diet 2), 14.8 (Diet 3), 19.5 (Diet 4), 22.8 (Diet 5) and 29.4% (Diet 6). Each diet was fed to quadruplicated groups of fish with initial average weight of 233 g in freshwater cages for 80 days. Results showed that there were significant linear and quadratic responses in growth performance, feed utilization, digestive ability and health status of sub-adult fish (P <.05). Final weight, specific growth rate (SGR), feed intake (FI), stomach protease activity, activity of lipase in pyloric caeca, activity of amylase in pyloric caeca and intestine showed a general increasing trend with increasing dietary protein level. Feed conversion ratio (FCR) decreased with increasing dietary protein level. No significant difference of intestinal morphology was observed in any of the groups (P >.05) except that the highest value for muscular layer thickness and density of goblet cells were found in Diet 6 treatment (P <.05). When examining health status, no negative effects were found in the antioxidative capacity of the intestine and liver (P >.05), however, the lowest value of plasma total anti-oxidative capacity (T-AOC) content and highest plasma malonaldehyde (MDA) content were shown in Diet 6 treatment (P <.05). There was no significant difference in plasma enzymes in any of the groups (P >.05) except for activities of aspartate aminotransferase (AST) and creatine kinase (CK), which increased as dietary lipid levels increased (P <.05). The expression of growth-related genes was at first significantly improved (P <.05) and then kept consistent (P >.05). Broken-line regression analysis of FCR showed that the minimum dietary lipid level of triploid rainbow trout was 23.3% in the present study. In summary, we found that triploid rainbow trout could use or tolerate high dietary lipid level (up to 29.4%) with no negative effect on fish growth, feed utilization, liver or intestine health. The minimum dietary lipid level for sub-adult triploid rainbow trout was estimated to be 23.3% based on FCR under the present conditions. • Based on the FCR, the minimum dietary lipid level for sub-adult triploid rainbow trout was estimated to be 23.3% dry matter. • Triploid rainbow trout could use dietary lipid level up to 29.4% without affectingfish growth, feed utilization and health. • High dietary lipid levels promoted growth-related gene expressions, leading to the fast growth of triploid rainbow trout. [ABSTRACT FROM AUTHOR]