Growth Of Trout Research Articles

Evaluating Inclusion of Commercial Pistachio By-Product as a Functional Ingredient in Rainbow Trout Fishmeal and Plant Meal-Based Diets

To meet the growing demand for sustainable aquaculture, plant proteins are being explored as alternative sources in fish diets. However, some plant proteins can have adverse health effects on fish, prompting research into functional feed ingredients to mitigate these issues. This study investigated pistachio shell powder (PSP), rich in antioxidants, as a functional feed ingredient for rainbow trout (Oncorhynchus mykiss). The effects of PSP inclusion (0%, 0.5%, 1%, 2%) on growth performance, intestinal health, and gut microbiota were assessed in fish fed either a fishmeal (FM) or plant meal (PM) diet over a 12-week feeding period. The results indicated that PSP inclusion at 1% significantly (p < 0.05) improved weight gain and growth performance in FM treatments, with no impact on growth in PM treatments. No significant differences were observed in other growth parameters, intestinal morphology, or oxidative stress markers, although a trend toward the downregulation of inflammatory genes was noted in PM treatments at 2% PSP inclusion. PSP inclusion did not significantly alter gut microbiota alpha diversity but affected beta diversity at the 0.5% level in the FM treatments (p < 0.05). Differential abundance analysis of gut microbiota revealed taxa-specific responses to PSP, particularly the genus Candidatus arthromitus, increasing in relative abundance with PSP inclusion in both the FM- and PM-based treatments. Overall, PSP inclusion up to 2% did not have significant adverse effects on the growth, intestinal health, or antioxidant status of rainbow trout.

Impact of dietary lysine on growth, nutrient utilization, and intestinal health in triploid rainbow trout (Oncorhynchus mykiss) fed low fish meal diets

Lysine is one of the essential amino acids for fish growth and development. This study investigated the effect of dietary lysine on growth performance, digestion, and intestinal health of triploid rainbow trout (Oncorhynchus mykiss) (initial body weight: 9.00 ± 0.33 g) fed a low fish meal diet (15 %). Five dietary lysine levels (3.66 %, 3.84 %, 4.19 %, 4.32 %, and 4.55 %) were evaluated for 56 days, with three replicates of 30 fish per level. The results showed that the weight gain rate (198.55 %), specific growth rate (1.95), and VSI were maximized when the dietary lysine level was 4.19 %. The 4.19 % lysine group exhibited minimum moisture (66.66 %) and maximum crude protein (15.47 %), with no significant differences in crude lipid and ash contents. Growth factors mTOR and 4EBP-1, on the other hand, had the highest expression in the 4.19 % group, while IGF-1 and S6K1 peaked in the 4.32 % group. The anti-inflammatory factors TGF-β, NF-κB, IL-4, and IL-10 peaked at different levels and then decreased with increasing lysine levels. The pro-inflammatory factor IL-1β, on the other hand, had the lowest expression at the 4.19 % level. Based on quadratic regression analysis of specific growth rate, the lysine requirement of triploid O. mykiss in low fish meal diets was 4.24 %.

Effect of Dietary Astragalus polysaccharides (APS) on the Growth Performance, Antioxidant Responses, Immunological Parameters, and Intestinal Microbiota of Coral Trout (Plectropomus leopardus)

The potential effects of Astragalus polysaccharides (APS) were evaluated in coral trout (Plectropomus leopardus). Five APS levels (0%, 0.05%, 0.10%, 0.15%, and 0.20%) were added to the diet of coral trout, and a 56-day growth trial (initial weight 18.62 ± 0.05 g) was conducted. Dietary APS enhanced growth performance, with the highest improvement observed in fish fed the 0.15% APS diet. This concentration also enhanced the antioxidant capacity and immunomodulation of the fish by regulating the expression of genes associated with antioxidant enzymes and immune responses. Intestinal microbiota analysis revealed that APS supplementation significantly increased the Chao1 index and relative abundance of beneficial bacteria (Firmicutes and Bacillus). A high level of APS (0.20%) did not provide additional benefits for growth and health compared to a moderate level (0.15%). These findings indicate that an optimal APS dose promotes growth, enhances antioxidant activity, supports immune function, and improves intestinal microbiota in coral trout. Based on a cubic regression analysis of the specific growth rate, the optimal APS level for the maximal growth of coral trout was determined to be 0.1455%.

Optimizing growth and mitochondrial function in rainbow trout, Oncorhynchus mykiss through eco-friendly dietary and changes in water temperature regimen strategies

Developing sustainable aquaculture remains a challenge, notably finding suitable alternatives to marine ingredients in carnivorous fish diets such as rainbow trout (Oncorhynchus mykiss) in changing climate. These new diets are especially important because rainbow trout are an ecologically and economically significant aquaculture species. Therefore, we investigated the impact of sustainable ingredients and water temperature manipulations on rainbow trout growth characteristics and mitochondrial function. A total of 432 fish were fed four isocaloric, isolipidic, and isonitrogenous diets comprised 40 % crude protein and 20 % lipid and formulated as diet 1 (animal-based protein +25 % fish oil/ 50 % plant oil/ 25 % terrestrial animal oil), or diet 2 (animal-based protein +100 % plant oil), or diet 3 (plant-based protein +25 % fish oil/ 50 % plant oil/25 % terrestrial animal oil), or diet 4 (plant-based protein +100 % plant oil) at 14 °C or 18 °C or 20 °C water temperature. Results showed percent weigh gain (PWG) and specific growth rate (SGR), feed efficiency (FE), and feed intake (FI) were significantly (P < 0.05) higher in fish reared at 14 °C and 18 °C compared to 20 °C. The PWG, FE, FI, and SGR levels were significantly (P < 0.05) higher for fish fed diets 1 and 2 than those fed diets 3 and 4. Dietary composition influenced whole-body proximate composition, while temperature affected protein, moisture, and lipid contents. For protein, lipid, and energy contents, temperature-diet interactions were significant (P < 0.05). There were differences in mitochondrial enzymatic activities in muscle, liver and intestine. Diet affected only complex V activity in the liver, whereas temperature significantly (P < 0.05) affected the activities of complexes II, III, and V. A temperature-dietary interaction was observed for complex V. The temperature regimens, but not dietary composition, affected muscle mitochondrial enzymatic activities. There were significant (P < 0.05) effects of temperature on complex III, IV, and citrate synthase activities in the intestine, whereas dietary composition had no significant impact (P > 0.05). Based on diet, temperature, and diet-temperature interactions effects, selected genes were expressed differently in different tissues. The nd1, cox2, cytb, cox1, atp6 and PPAR-α genes were significantly influenced by diet and temperature interactions in muscle, liver and intestine. Overall, our results showed that both temperature and dietary composition had significant effects on growth characteristics, proximate composition, mitochondrial enzymatic activities, and their interactions on gene expression levels in rainbow trout. These findings underscore the importance of considering these factors in the development of plant-based aquafeeds in order to optimize growth and productivity.

Dietary astaxanthin alleviates negative changes of flesh quality, long chain unsaturated fatty acids content and muscle growth on rainbow trout (Oncorhynchus mykiss) induced by black soldier fly oil via mammalian target of rapamycin and AMP-activated protein kinase α pathway: Evidence of transcripts and proteomics

This study evaluated the effect of black soldier fly (Hermetia illucens) larvae oil (BO) produced by a novel technique, subcritical butane extraction, on the muscle growth, flesh quality and lipid nutrients of rainbow trout (Oncorhynchus mykiss), and investigated the alleviating mechanisms of dietary astaxanthin supplementation. Two hundred and forty fish (215.16 ± 2.30 g) were distributed to three groups with four replicates. Fish were fed three experimental diets for 8 weeks: the control diet (CD diet), total fish oil of the CD diet was replaced with BO to formulate the BO100 diet, and then 1 g/kg astaxanthin was supplemented with the BO100 diet to formulate the AST diet. Results showed that the final body weight and the sarcomere length of fillet were significantly increased and the protein phosphorylation levels of mammalian target of rapamycin (mTOR) and p70 S6 kinase were enhanced in the BO100 group compared to the CD group (P < 0.05). However, there was a reduction in the hardness, springiness and chewiness of fillets, with a decrease in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels in the fish of the BO100 group (P < 0.05). Supplementation of astaxanthin in the BO100 diet mitigated the impairment of springiness and chewiness and further promoted the sarcomere length of fillet (P < 0.05). Furthermore, dietary astaxanthin partially restored the EPA and DHA content of fillet by increasing the phosphorylation levels of serine/threonine kinase (AKT) and AMP-activated protein kinase α (AMPKα) (P < 0.05) and activating the gene expression of unsaturated fatty acid synthesis. To conclude, BO produced by subcritical butane extraction can be a readily available oil source for rainbow trout feed that can be used to promote muscle growth in rainbow trout. Further dietary astaxanthin supplementation can alleviate BO-induced lipid accumulation, restore DHA levels and improve the flesh quality of rainbow trout fillet.

Activin Signaling Pathway Specialization During Embryonic and Skeletal Muscle Development in Rainbow Trout (Oncorhynchus mykiss).

Activin signaling is essential for proper embryonic, skeletal muscle, and reproductive development. Duplication of the pathway in teleost fish has enabled diversification of gene function across the pathway but how gene duplication influences the function of activin signaling in non-mammalian species is poorly understood. Full characterization of activin receptor signaling pathway expression was performed across embryonic development and during early skeletal muscle growth in rainbow trout (RBT, Oncorhynchus mykiss). Rainbow trout are a model salmonid species that have undergone two additional rounds of whole genome duplication. A small number of genes were expressed early in development and most genes increased expression throughout development. There was limited expression of activin Ab in RBT embryos despite these genes exhibiting significantly elevated expression in post-hatch skeletal muscle. CRISPR editing of the activin Aa1 ohnolog and subsequent production of meiotic gynogenetic offspring revealed that biallelic disruption of activin Aa1 did not result in developmental defects, as occurs with knockout of activin A in mammals. The majority of gynogenetic offspring exhibited homozygous activin Aa1 genotypes (wild type, in-frame, or frameshift) derived from the mosaic founder female. The research identifies mechanisms of specialization among the duplicated activin ohnologs across embryonic development and during periods of high muscle growth in larval and juvenile fish. The knowledge gained provides insights into potential viable gene-targeting approaches for engineering the activin receptor signaling pathway and establishes the feasibility of employing meiotic gynogenesis as a tool for producing homozygous F1 genome-edited fish for species with long-generation times, such as salmonids.

Подбор параметров моделей роста радужной форели

The purpose of the presented work is to assess the adequacy and selection of optimal parameters of mathematical models of fish growth in application to forecasting the growth of aquaculture trout in closed water supply installations (CWSI). To perform the assessment and comparison, 8 nonlinear mathematical models of fish growth were considered. Tabular (parametric) models of feed for trout cultivation in the CWSI were taken as a standard, and on their basis the selection of optimal parameters was carried out, bringing each of the mathematical models closer to the standard one. The results were compared using an estimate of the standard error, the Akaike information criterion adjusted for a small sample size, and the Bayesian information criterion. As a result, the parameters providing the best approximation of the considered mathematical models of fish growth to the reference tabular function are obtained. As a result of the error estimation, it was found that the three-parameter von Bertalanfi model demonstrates the best accuracy. At the same time, other models (with the exception of exponential) have also demonstrated accuracy sufficient for practical use. The practical significance of the work is the conclusions on the adequacy of the use of nonlinear mathematical models for modeling trout growth in the CWSI, as well as the presented model parameters that provide the best approximation to the reference tabular function.

Effect of Dietary β-Glucan on Growth Performance, Antioxidant Responses, and Immunological Parameters of Coral Trout (Plectropomus leopardus)

Although β-glucan has diverse benefits for fish health, the potential adverse impacts of excessive supplementation are poorly understood. This study investigated the optimal dosage of β-glucan for coral trout and explored the adverse effects of excessive supplementation. The results revealed that moderate β-glucan supplementation (1) significantly enhanced the weight gain rate and specific growth rate (SGR); (2) significantly improved the intestinal villus length (0.10%), muscle thickness (0.05–0.15%), and α-amylase and chymotrypsin activities (0.05–0.15%); (3) significantly increased liver catalase (CAT), glutathione reductase (GR), alkaline phosphatase, complement 3, immunoglobulin M (IgM), lysozyme, serum superoxide dismutase, CAT, glutathione peroxidase, GR, total antioxidant capacity, acid phosphatase, complement 4, and IgM activities and significantly reduced malondialdehyde contents; (4) upregulated genes in the liver associated with copper-zinc superoxide dismutase (SOD-1), manganese superoxide dismutase (SOD-2), CAT, GSH-Px1a, ACP6, AKP, LZ-c, IgM, C3, and C4-b. However, 0.20% β-glucan significantly inhibited the growth performance of coral trout compared with 0.10% β-glucan. Thus, 0.10% β-glucan represents the optimal dosage for promoting growth, antioxidant activity, and immune responses in coral trout, while higher β-glucan levels weakened these beneficial effects. With an SGR established by a cubic regression analysis, the optimal level of β-glucan for maximal growth of coral trout is 0.082%. This study provides new insights into the health impacts of β-glucan on fish.

Comparison of growth, carcass and meat quality characteristics of triploid and diploid Black Sea trout (Salmo trutta labrax) under laboratory conditions

Comparison of growth, carcass and meat quality characteristics of triploid and diploid Black Sea trout (Salmo trutta labrax) under laboratory conditions

The effect of various dietary MUFA content and n-6/n-3 ratios on rainbow trout (Oncorhynchus mykiss) fed on a whole plant protein based diet: growth performance, digestive enzymes activity, intestinal morphometry and fatty acids profile of muscle and liver.

The effect of diets with various dietary MUFA content and n-6/n-3 ratios, diets 1 (55.33, 1.00), 2 (25.30, 1.00), 3 (55.13, 2.05), 4 (24.92, 2.03), 5 (54.94, 8.06) and 6 (24.91, 8.06) and a control diet with fish oil (FO), diet 7 (33.60, 5.97), was studied on growth and digestive physiology of rainbow trout, Oncorhynchus mykiss. Juveniles, 14.65g ± 0.17, were fed the experimental diets for eight weeks. Those fish fed diet 1 (55.33, 1.00) had the lowest growth and nutritional indices, while fish fed diet 6 (24.91, 8.06) possessed the highest indices. However, fish fed D7 (33.60, 5.97) was intermediate in this regard. Proximate body composition results revealed no significant differences among various experimental groups (P > 0.05). Fish fed on diet 1 possessed the highest alkaline protease activity, while fish raised on diet 2 showed the lowest enzyme activity (P < 0.05). Fish fed on diets 1, 3 and 4 had the highest lipase activity (P > 0.05). Amylase activity and intestinal parameters did not differ among groups (P > 0.05). MUFA contents of liver and muscle reflected the MUFA contents of the diets; however, liver PUFA contents was not affected by dietary PUFA contents (P < 0.05). However, 18:3n-3 contents of liver decreased as dietary n-6/n-3 ratio increased (P < 0.05). Furthermore, the liver 20:4n-6 contents considerably increased as dietary n-6/n-3 increased to 8.06 (P < 0.05). Muscle 22:6n-3 content of groups 1 to 6 was lower than group 7 (P < 0.05). In conclusion, rainbow trout was considerably capable of de novo synthesis of 22:6n-3. Meanwhile, increasing dietary n-6/n-3 ratio to 8.06 decreased the muscle 22:6n-3 content which requires further considerations regarding fish immune competence and nutritional quality for human consumption.

Optimizing valine supplementation in low-fish meal diets for enhanced growth, digestion, antioxidant capacity, and intestinal health of triploid rainbow trout (Oncorhynchus mykiss)

This study evaluates the effects of valine on the growth, digestion, antioxidant capacity, and intestinal health of triploid rainbow trout (Oncorhynchus mykiss) fed a low fish meal diet (10 %). The trouts with an initial body weight of 15.08±0.20 g were fed with five different isonitrogenous and isoenergetic diets containing levels of valine: 0.86 % (G1), 1.79 % (G2), 2.43 % (G3), 3.02 % (G4), and 3.68 % (G5) for 56 days. The results showed that the weight growth rate and specific growth rate of the 2.43 % group were significantly higher than those of the 0.86 % control group (P<0.05). The intestinal villus length and muscle layer thickness propria were significantly increased in the 3.02 % group compared to the control group (P<0.05). The activities of intestinal protease, amylase, superoxide dismutase, catalase, and lysozyme in the 2.43 % group were significantly higher than those in the control group (P<0.05). The levels of interleukin-8 and tumor necrosis factor-alpha were lowest in the 3.02 % group, while the IL-10 level was highest in the 3.02 % group (P<0.05). Elevated levels of valine in the dietary regimen correlated positively with the upregulation of pivotal genes associated with antioxidant mechanisms, notably nuclear factor erythroid 2-related factor 2 (Nrf2), NAD(P)H: quinone oxidoreductase 1 (NQO1), and thioredoxin (Trx). Additionally, the expression of genes implicated in the synthesis of tight junction proteins, including occludin, claudin 7b, and claudin 15, exhibited significant augmentation with escalating valine concentrations in the feed. In conclusion, dietary valine enhanced the growth, digestive and absorptive capabilities, antioxidant capacity, and intestinal health of O. mykiss. An analysis based on a quadratic curve model, which incorporates specific rates of growth and weight gain, establishes that the optimal dietary valine requirement for triploid O. mykiss consuming a 10 % fish meal diet ranges between 2.43 % and 2.69 %.

Zinc nutrition at first feeding imprints a programming effect on growth and hepatic lipid metabolism in juvenile rainbow trout

The objective of this study was to determine whether supplementation with deficient zinc (Zn) or/and excess copper (Cu) in the first-feeding diet of rainbow trout fry influenced the growth and physiological regulation of juvenile fish subjected to similar challenge feeds again. The feeding trial lasted for 24 weeks and had three phases. In phase I, rainbow trout fry was treated with one of four different plant-based feeds containing or exempting Zn or Cu supplementation (coded Zn-Cu-, Zn+Cu-, Zn-Cu+, Zn+Cu+) for 6 weeks. Thereafter, all groups were fed a common commercial feed for the next 12 weeks (phase II). In phase III, all groups were fed with the “challenge diet” for another 6 weeks which was the basal diet (Zn-Cu-) except that the vegetable oils were replaced by fish oil. The results demonstrated that fish fed a Zn+ diet at first feeding increased larval growth (phase-I), but it had no effect on growth at the end of phase II when fed commercial feeds. In phase III, when re-introduced to a Zn- challenge diet, the feed intake and growth of juveniles with Zn+ history significantly increased, with reduced feed efficiency. Fish growth was neither influenced by dietary Cu levels or by the dietary Cu history in any of the growth phases, but dietary Cu excess (Cu+) reduced body lipid and energy content in fry. In phase I, lower whole-body Zn concentration was observed in the fry of Zn- group compared to Zn+, while the contrary was observed in the juvenile fish as affected by dietary Zn history (phase III). In addition, Zn- dietary history showed increased levels of PUFA and higher mRNA expression of fatty acid biosynthesis genes in the liver. To conclude, early-stage dietary Zn+ history improved growth of juvenile rainbow trout, while dietary Zn- history exhibited signs of improved fatty acid biosynthesis capacity in the liver.

Replacing Fishmeal and Fish Oil with Complex Protein and Canola Oil: Effect on Organoleptic and Nutritional Quality of Triploid Rainbow Trout (Oncorhynchus mykiss).

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.

Growth of brown trout in the wild predicted by embryo stress reaction in the laboratory.

Laboratory studies on embryos of salmonids, such as the brown trout (Salmo trutta), have been extensively used to study environmental stress and how responses vary within and between natural populations. These studies are based on the implicit assumption that early life-history traits are relevant for stress tolerance in the wild. Here we test this assumption by combining two data sets from studies on the same 60 families. These families had been experimentally produced from wild breeders to determine, in separate samples, (1) stress tolerances of singly kept embryos in the laboratory and (2) growth of juveniles during 6 months in the wild. We found that growth in the wild was well predicted by the larval size of their full sibs in the laboratory, especially if these siblings had been experimentally exposed to a pathogen. Exposure to the pathogen had not caused elevated mortality among the embryos but induced early hatching. The strength of this stress-induced change of life history was a significant predictor of juvenile growth in the wild: the stronger the response in the laboratory, the slower the growth in the wild. We conclude that embryo performance in controlled environments can be a useful predictor of juvenile performance in the wild.

Enhancing Growth and Intestinal Health in Triploid Rainbow Trout Fed a Low-Fish-Meal Diet through Supplementation with Clostridium butyricum

Enhancing Growth and Intestinal Health in Triploid Rainbow Trout Fed a Low-Fish-Meal Diet through Supplementation with Clostridium butyricum

Enzyme-treated microalgal co-product diets for rainbow trout aquaculture: Supporting fish growth, phosphorus digestibility, and reducing phosphorus waste emission

Aquaculture is one of the fastest-growing food sectors, producing almost 50% of fish for human consumption worldwide. However, relying on fish meal and oil for aquaculture diets is not sustainable economically or environmentally. Aquaculture feeds also contain terrestrial plant ingredients with indigestible forms of phosphorus (P), of which 70%–80% can be released into aquatic environments. This P influx contributes to eutrophication of freshwater ecosystems that can lead to anoxic conditions. This study explores a more sustainable diet for salmonids, an important and valuable seafood. Our aim was to test ingredients with highly digestible forms of P in nutritionally balanced portions to support fish growth and reduce P loading. We determined the digestibility of three feeds containing raw, extruded, and enzymatically processed microalgal co-product of Nannochloropsis oculata compared to a conventional diet. We also quantified how much P was retained and excreted. We detected highest growth in trout fed enzymatically processed co-product feed, though it was not statistically different (p = 0.846) from growth of fish fed the reference or other co-product diets. The enzyme-treated, microalgal co-product ingredient and diet had comparable values for P digestibility and solid P excretion to the reference diet, but the lowest average solid P excretion of all test diets. Trout fed the enzyme-treated diet had the highest P retention, while the reference diet had the lowest (p = 0.0429). Trout fed the enzyme-treated diet had the lowest (p = 0.0174) and negative dissolved P excretion, while those fed the reference diet had the highest. Results showed that enzyme-treated N. oculata co-product maintains digestibility, increases P retention, and reduces dissolved P excretion compared to the reference diet in rainbow trout. These findings encourage follow-up research to design and test growth performance of diets containing enzyme-treated microalgal co-product as sustainable trout aquafeed.

Mechanism of Ligilactobacillus salivarius GX118 in Regulating the Growth of Rainbow Trout (Oncorhynchus mykiss) and Resistance to Aeromonas salmonicida Infection

Lactic acid bacteria Ligilactobacillus salivarius has been shown to be a substitute for antibiotics in the treatment of bacterial disease in high animals. However, its beneficial mechanism in fish farming is still unclear. This study evaluated the antagonistic effects of the Ligilactobacillus salivarius GX118 strain on Aeromonas salmonicida and its regulation of rainbow trout growth in vivo and in vitro. The results found that GX118 produces an antibacterial substance that can directly destroy the cell wall of A. salmonicida. Whole-genome sequencing of GX118 revealed that Enterolysin A is a type III bacteriocin with antibacterial properties. An in vivo experiment showed that the supplementation of GX118 in diet competitively inhibited the colonization of A. salmonicida in the intestine. In addition, it was able to improve the growth performance of rainbow trout within a 21-day feeding experiment. The supplementation of GX118 increased the diversity of gut microbiota, in which the abundance of Bacteroidota, Blautia, and Rhodobacteraceae increased. In addition, the use of GX118 activated the expression of IFN-γ and NF-κB genes and reduced the expression level of IL-6 and IL-8, thus exhibiting a certain effect on activating the immunity of rainbow trout. This study provides a scientific basis for the development of antibacterial probiotics in the healthy farming of rainbow trout.

Gut physiology of rainbow trout (Oncorhynchus mykiss) is influenced more by short-term fasting followed by refeeding than by feeding fishmeal-free diets

Supplementing a fishmeal-free diet with yeast extract improves rainbow trout (Oncorhynchus mykiss) growth performance and modulates the hepatic and intestinal transcriptomic response. These effects are often observed in the long term but are not well documented after short periods of fasting. Fasting for a few days is a common practice in fish farming, especially before handling the fish, such as for short sorting, tank transfers, and vaccinations. In the present study, rainbow trout were subjected to a 4-day fast and then refed, for 8 days, a conventional diet containing fishmeal (control diet) or alternative diets composed of terrestrial animal by-products supplemented or not with a yeast extract. During the refeeding period alone, most of the parameters considered did not differ significantly in response to the different feeds. Only the expression of claudin-15 was upregulated in fish fed the yeast-supplemented diet compared to the control diet. Conversely, fasting followed by refeeding significantly influenced most of the parameters analyzed. In the proximal intestine, the surface area of villi significantly increased, and the density of goblet cell tended to decrease during refeeding. Although no distinct plasma immune response or major signs of gut inflammation were observed, some genes involved in the structure, complement pathway, antiviral functions, coagulation, and endoplasmic reticulum stress response of the liver and intestine were significantly regulated by refeeding after fasting. These results indicate that short-term fasting, as commonly practiced in fish farming, significantly alters the physiology of the liver and intestine regardless of the composition of the diet.

Effect of dietary fish oil sparing with blended vegetable oils on growth, fatty acid composition and lipid-metabolism-related genes expression in juvenile rainbow trout (Oncorhynchus mykiss)

Abstract A nutritional study was conducted to evaluate the influence of dietary fish oil (FO) sparing by using a mixture of vegetal oils (VO) on rainbow trout (Oncorhynchus mykiss) juveniles (30.0 g). A basal diet was supplemented with the experimental oils at a 10% level, including FO (FO diet), a blend of VO (sunflower, soybean and rapeseed oils with a 1:1:1 ratio), and a mixture (1:1 ratio) of FO and the blends of VO (MIX). In a raceway system, 450 fish were stocked in nine rectangular concrete tanks (50 fish/ tank−1). Three experimental diets, with three replicates each, were offered to fish up to visual satiation for eight weeks. Growth performance did not change among groups (P&gt;0.05). The highest and lowest proportions of n-3 polyunsaturated fatty acids (PUFA), n-3 long chain-PUFA, especially docosahexaenoic acid, and n-3/n-6 PUFA ratio were in the whole body of FO and the VO groups, respectively (P&lt;0.05). Serum catalase and glutathione peroxidase activities in VO group were higher than others. Serum superoxide dismutase activity in fish fed FO and VO diets was higher than MIX group (P&lt;0.05). VO group had higher serum lysozyme, alternative complement pathway, and total immunoglobulin levels than other experimental groups. MIX group had highest serum triglyceride, cholesterol, and low-density lipoproteins. Serum high-density lipoproteins, aspartate aminotransferase, and alanine aminotransferase levels in VO treatment were in the lowest level compared to others (P&lt;0.05). The highest relative transcription levels of fatty acid synthase, delta-6 fatty acyl desaturase, and apolipoprotein b-100 genes were in the liver of fish fed the MIX diet. The relative transcription level of the fatty acid-binding protein1 gene did not change (P&gt;0.05). In summary, the results of this study revealed that dietary FO sparing with VO did not adversely affect the growth and health indices of rainbow trout; nevertheless, it had adverse effects on its nutritional values by reducing whole-body n-3 LC-PUFA content.

Influence of salinity on rainbow trout (Oncorhynchus mykiss) smolt development and postsmolt performance

Rainbow trout aquaculture has large potential for growth, but requires better understanding of aspects like smoltification and its effect on trout performance after seawater transfer. The present study examined the effect of three different salinities (fresh water, 3–5 ‰ and 15–16 ‰) on smoltification and growth of rainbow trout (70 ± 10 g) reared under constant light between March–June 2018; it also documented hypoosmoregulatory performance and growth of trout from all salinity treatments transferred to full seawater at three different times (Transfer 1: 26 April; Transfer 2: 24 May; Transfer 3: 21 June). Smolt development was assessed with markers commonly used for Atlantic salmon like gill Na+, K+-ATPase activity, gill mRNA transcription of key genes (nkaα1a, nkaα1b and nkcc1a) and plasma concentration of Cl− and Na+. Results evidenced that trout in brackish water experienced an earlier onset of smoltification, displayed by rapid changes in mRNA transcription of the ATPase α-isoforms nkaα1a (freshwater isoform) and nkaα1b (seawater isoform), which, in turn, induced an earlier peak of the Na+, K+-ATPase (NKA) activity. However, smoltification also commenced and progressed in fresh water most likely as a result of reaching a certain size. The salinity treatment did not influence growth during the smoltification period. After seawater transfer, all treatments in Transfer 1 (26 April) displayed the best capacity to acclimatize to full seawater (with clear upregulations of nkaα1b and nkcc1a after seawater entry) and the highest growth, compared to all treatments in Transfers 2 and 3. In contrast, few differences in growth and smoltification markers occurred between salinity treatments within each of the seawater transfers. This suggests that trout in the first transfer had the best smolt condition (were at the peak of smolt window), which allowed them to adapt and grow better in seawater. Overall, such results indicate that timing of seawater transfer can be more important for trout performance in the grow-out phase in the sea than the water salinity during the early rearing period. As such, although brackish water can be used to induce rainbow trout smoltification, transferring the fish at the peak of the smolt window can increase chances for best seawater performance.