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A two-phase feeding study evaluating performance of rainbow trout and comparing luminal and mucosal gastrointestinal tract (GIT) bacterial community compositions when fed two alternative protein diets in two rearing systems was conducted. Alternative protein diets (animal protein and plant protein diets) balanced with crystalline amino acids: lysine, methionine and threonine or unbalanced, were fed to rainbow trout in two separate water systems (recirculating (RR) and flow-through (FF)) for a period of 16 weeks. The four diets, each contained 38% digestible protein and 20% fats, were fed to rainbow trout with an average weight of 12.02 ± 0.61 g, and sorted at 30 fish/tank and 12 tanks per dietary treatment. Phase 1 lasted for 8 weeks after which fish from each tank were randomly divided, with one-half moved to new tanks of the opposing system (i.e. from RR to FF and vice versa). The remaining halves were retained in their initial tank and system, and fed their original diets for another 8 weeks (phase 2). After the 16th week, 3 fish/tank were sampled for each of proximate analysis, body indexes and 16S rRNA analysis of GIT microbiota. Fish weight (P = 0.0008, P = 0.0030, P<0.0010) and body fat (P = 0.0008, P = 0.0041, P = 0.0177) were significantly affected by diet, diet quality (balanced or unbalanced) and system, respectively. Feed intake (P = 0.0008) and body energy (P<0.0010) were altered by system. Body indexes were not affected by dietary treatment and water systems. Compositional dissimilarities existed between samples from the rearing water and GIT locations (ANOSIM: (R = 0.29, P = 0.0010), PERMANOVA: R = 0.39, P = 0.0010), but not in dietary samples (ANOSIM: R = 0.004, P = 0.3140, PERMANOVA: R = 0.008, P = 0.4540). Bacteria were predominantly from the phyla Proteobacteria, Firmicutes and Bacteroidetes. Their abundance differed with more dissimilarity in the luminal samples (ANOSIM: R = 0.40, P = 0.0010, PERMANOVA: R = 0.56, P = 0.0010) than those from the mucosal intestine (ANOSIM: R = 0.37, P = 0.0010, PERMANOVA: R = 0.41, P = 0.0010). Bacteria generally associated with carbohydrate and certain amino acids metabolism were observed in the mucosal intestine while rearing water appeared to serve as the main route of colonization of Aeromonas and Acinetobacter in the rainbow trout.

Aquaculture feeds with optimum digestible starch levels can provide benefits but only through the continued identification and characterization of the available nutrient content of novel or lesser utilized starch sources for a larger variety of aquatic species. To address this literature gap, in vivo digestibility trials were conducted in rainbow trout and hybrid striped bass to determine the available nutrient content of commercially sourced U.S. grain sorghum hybrids. Based on digestibility data, a regression design was employed to test the replacement of wheat flour with U.S. grain sorghum in practical‐type diets for rainbow trout and hybrid striped bass at four inclusion levels (0%, 5%, 10%, and 20%). All diets were formulated to contain 40% digestible protein and 18% crude lipid, and balanced to available lysine, methionine, threonine, and phosphorus to targets of 3.82, 1.30, 2.14, and 0.6, respectively, prior to cooking extrusion. For the growth trials, 10 rainbow trout (59.1 ± 0.07 g, initial weight) or 10 hybrid striped bass (27.1 ± 0.1 g) were randomly stocked into triplicate replicate tanks per diet (300 or 500 L, respectively) and fed for eight or nine weeks, respectively to assess effects on growth performance. No significant negative effects of U.S. grain sorghum inclusion on hybrid striped bass final fish weight, growth rate expressed as a percent increase, feed conversion ratio, feed intake, body condition indices, or whole‐body proximate composition were observed. The effects of 20% red grain sorghum inclusion on rainbow trout final fish weight were explained by the linear model: Final fish weighg=248−1.0Sorghum inclusion level $$ \\mathrm{Final}\\ \\mathrm{fish}\\ \\mathrm{weigh}\\ \\left(\\mathrm{g}\\right)=248-1.0\\ \\left(\\mathrm{Sorghum}\\ \\mathrm{inclusion}\\ \\mathrm{level}\\right) $$ . The reduced growth observed in rainbow trout at the 20% inclusion level underscores the need for additional research to examine the potential beneficial effects of further sorghum processing and optimize feed extrusion parameters when U.S. grain sorghum is used in place of wheat flour.

The world population is increasing, and our current agricultural practices are not sustainable enough to address the concerns. Alternative proteins including plant-based proteins would provide a more sustainable source of food and feed ingredients. Among food systems, the aquaculture industry is rapidly growing, while still depending on marine sources as a main source of protein. Thus, using alternative plant-based proteins as a source for developing aquafeed would make this industry more viable. Sorghum is a valuable grain with high protein contents, proper mineral and fatty acids balance, and is available all around the world. However, sorghum has not been used widely for aquafeed development. In this review article, we cover sorghum production, composition, sorghum as a protein source for aquafeed development, and bioprocessing methods for enhancing the quality of sorghum.

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.

Microalgal docosahexaenoic acid (DHA) and astaxanthin (AST) may substitute for fish oil and synthetic AST in aquafeeds. This study explored the effects and mechanisms of those substitutions on AST metabolism and redox status of rainbow trout fed plant protein meal (PM)- or fishmeal (FM)-based diets. Two parallel experiments (PM vs. FM) were performed with 612 juvenile rainbow trout for 16 weeks as a 2 × 3 factorial arrangement of treatments with two AST sources (synthetic (SA) vs. microalgal (AA), at 80 mg/kg) and three levels (0, 50, and 100%) of fish oil substitutions with DHA-rich microalgae. The fish oil substitutions exhibit main effects (p < 0.05) and/or interactive effects (p < 0.05) with the source of AST on AST deposition, malondialdehyde and glutathione concentrations, and mRNA levels and activities of major redox enzymes (glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), and superoxide dismutase (SOD)) in the muscle and liver of trout fed both diet series. The AST source produced only differences in tissue AST deposition (p < 0.05) and number of metabolites. In conclusion, the substitutions of fish oil by the DHA-rich microalgae exerted more impacts than those of SA by AA on redox status and functional expression of antioxidant enzymes in the tissues of rainbow trout.

Prebiotics have successfully been used to prevent infectious diseases in aquaculture and there is an increasing amount of literature that suggests that these products can also improve alternative protein utilization and digestion. Therefore, the objective of this study was to examine whether prebiotic supplementation increased the growth efficiency, intestinal health, and disease resistance of cutthroat trout fed a high level of dietary soybean meal. To achieve this objective, juvenile Westslope cutthroat trout (Oncorhynchus clarkii lewisi) were fed a practical type formulation with 0 or 30% dietary soybean meal with or without the commercial prebiotic (Grobiotic-A) prior to experimental exposure to Flavobacterium psychrophilum. Juvenile Westslope cutthroat trout (initial weight 7.8 g/fish ±SD of 0.5 g) were stocked at 30 fish/tank in 75 L tanks with six replicate tanks per diet and fed their respective diets for 20 weeks. Final weights of Westslope cutthroat trout were affected by neither dietary soybean meal inclusion level (P = 0.9582) nor prebiotic inclusion (P = 0.9348) and no interaction was observed (P = 0.1242). Feed conversion ratios were similarly not affected by soybean meal level (P = 0.4895), prebiotic inclusion (P = 0.3258) or their interaction (P = 0.1478). Histological examination of the distal intestine of Westslope cutthroat trout demonstrated increases in inflammation due to both increased soybean meal inclusion level (P = 0.0038) and prebiotic inclusion (P = 0.0327) without significant interaction (P = 0.3370). Feeding dietary soybean meal level at 30% increased mortality of F. psychrophilum cohabitation challenged Westslope cutthroat trout (P = 0.0345) while prebiotic inclusion tended to decrease mortality (P = 0.0671). These results indicate that subclinical alterations in intestinal inflammation levels due to high dietary inclusion levels of soybean meal could predispose Westslope cutthroat trout to F. psychrophilum infection.

The ability of high‐value plant protein concentrates to replace fish meal and other expensive animal proteins in diets for rainbow trout depends on their available nutrient composition, cost and consistency. The aim of this study was to assess the effects of two novel corn protein products (ANDVantage™ 40Y and ANDVantage™ 50Y, The Andersons, Inc.) on the growth performance of juvenile rainbow trout. Two parallel replacement series were applied with test products included at 0%, 7.5%, 15%, 22.5%, and 30% diet dry weight replacing dietary fish meal and poultry meal on a digestible protein (DP) basis. All diets were formulated to 42% DP and 18% crude lipid, supplemented with Lys, Met, and Thr to targets of 3.8%, 1.3%, and 2.1%, respectively, and manufactured by cooking extrusion. Diets were randomly assigned to triplicate tanks of rainbow trout (Oncorhynchus mykiss, Troutlodge Inc., Sumner, WA) with a mean initial weight of 38 ± 0.7 g (mean ± SD). Fish were cultured in poly tanks (320 L) at n = 20 fish per tank in a recirculating system with a flow rate of 4–6 L min−1, temperature at 15°C, and a 13:11 light:dark cycle, and fed twice daily to apparent satiation 6 days per week for 12 weeks. Including ANDVantage products at levels above 22.5% decreased growth (gram gain per fish, p < 0.0001). A significant interaction was observed for feed conversion ratio (FCR; p < 0.0001) wherein fish fed ANDVantage™ 40Y had significantly higher FCR than fish fed ANDVantage™ 50Y when fed levels above 22.5%. Optimized inclusion levels, determined by regression analysis for combined data or for each ingredient when interactive effects occurred, indicate that maximum inclusion levels for ANDVantage™ 40Y and ANDVantage™ 50Y in rainbow trout diets range from 13.5% to 21.5% depending on the performance variable assessed.

An in vivo trial was conducted to determine the apparent digestibility coefficients (ADCs) of insect meals for rainbow trout, Oncorhynchus mykiss. Rainbow trout (approximately 370 g ± 23 g, mean ± SD initial weight) were stocked 25 per tank into 400-liter tanks. Fish were fed a reference diet, or 1 of 5 test diets created by blending the reference diet in a 70:30 ratio (dry-weight basis) with menhaden fish meal (MFM), 2 house cricket (Acheta domesticus) meals (cricket A and cricket B), Galleria mellonella meal, and yellow mealworm (Tenebrio molitor) meal. Diets were assigned to 3 replicate tanks of fish and fed twice daily for 14 days prior to fecal collection. Ingredients, diets, and fecal matter were analyzed in duplicate for proximate, mineral, and amino acid composition. House cricket meals were 67.3% and 69.0% protein (CP) and 16.6% and 17.1% lipid (CL), for house cricket A and B, respectively. Yellow mealworm meal contained 56.5% CP and 27.7% CL, and G. mellonella larvae meal contained 32.5% CP and 54.2% CL. Protein ADCs were 78.9 for G. mellonella larvae meal, 78.0 for yellow mealworm meal, and 76.5 for house cricket A and not different from the MFM protein ADC of 76.6, while house cricket B protein ADC was 65.8 and was significantly lower than the MFM protein ADC (F = 7.39; df = 4,14; P = 0.0049).Together, these nutritional values suggest house crickets, and yellow mealworms show promise as alternative protein sources in salmonid feeds, with the potential of G. mellonella as an alternative lipid source.

This study examined supplementation of a novel yeast product containing Pichia guilliermondii on juvenile rainbow trout, Oncorhynchus mykiss, growth, and disease resistance. In two separate trials, fish (initial weight 6.2 and 10.6 g, respectively), were fed an extruded diet (41% digestible protein and 18% crude lipid) supplemented with 0.3 or 0.6% P. guilliermondii alone or 0.3% P. guilliermondii with a dietary gut supplement at 0.1%. Prior to the end of each trial, a subsample of fish from each tank was exposed by immersion to Yersinia ruckeri (Trial 1) or injection with Flavobacterium pyschrophilum (Trial 2). At the conclusion of the trials, supplementation of either P. guilliermondii or the gut supplement improved growth and food conversion efficiency in rainbow trout when fed for 16‐weeks. No effects of supplementation on mortality were observed. These results suggest potential as functional additives; however, additional investigation regarding the efficacy of whole‐cell and disrupted wall components of P. guilliermondii is needed to better assess their potential effects on rainbow trout immune responses.

Microalgal docosahexaenoic acid (DHA) and astaxanthin (AST) may substitute for fish oil and synthetic AST in aquafeeds. This study explored the effects and mechanisms of those substitutions on AST metabolism and redox status of rainbow trout fed plant protein meal (PM)- or fishmeal (FM)-based diets. Two parallel experiments (PM vs. FM) were performed with 612 juvenile rainbow trout for 16 weeks as a 2 × 3 factorial arrangement of treatments with two AST sources (synthetic (SA) vs. microalgal (AA), at 80 mg/kg) and three levels (0, 50, and 100%) of fish oil substitutions with DHA-rich microalgae. The fish oil substitutions exhibit main effects (p < 0.05) and/or interactive effects (p < 0.05) with the source of AST on AST deposition, malondialdehyde and glutathione concentrations, and mRNA levels and activities of major redox enzymes (glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), and superoxide dismutase (SOD)) in the muscle and liver of trout fed both diet series. The AST source produced only differences in tissue AST deposition (p < 0.05) and number of metabolites. In conclusion, the substitutions of fish oil by the DHA-rich microalgae exerted more impacts than those of SA by AA on redox status and functional expression of antioxidant enzymes in the tissues of rainbow trout.