This study addressed the escalating demand for aquatic feed by exploring the potential of alfalfa nutrient concentrate (ANC) as feed ingredient for rainbow trout. Test diets contained varying ANC levels (0%, 5%, 10%, 15%, and 20%) to replace fishmeal (32% in the 0% ANC diet) to achieve equal digestible protein and were processed using a cooking extrusion method. Analysis of feed pellets showed that pellet density increased with ANC levels (P < 0.001), resulting in sinking pellets at 20% ANC. Water stability and durability were improved while oil leakage decreased with increasing ANC levels (P < 0.05). Two feeding trials were conducted to test the diets in flow-through water systems with three replicates per diet. The first 10-week trial evaluated their impact on feeding, fecal physical quality, and the apparent digestibility coefficient (ADC) of dietary nutrients in rainbow trout (initial body weight 18.0 ± 0.2 g). ANC inclusion did not impact the palatability and satiety feed intake of the fish (P > 0.05). However, the ADC of dry matter and phosphorus significantly decreased in fish fed the 20% ANC diet (P < 0.05). The second 9-week trial investigated the growth performance, nutrition quality, and metabolism of rainbow trout (initial body weight 19.0 ± 0.2 g). While all fish exhibited substantial growth, fish fed diets with 10% to 20% ANC displayed lower specific growth rate and higher feed conversion ratio compared to those fed with 0% or 5% ANC (P < 0.05). The whole body protein content was higher in fish fed 5% ANC compared to all other treatments (P = 0.030). The biochemical parameters of plasma were similar across treatments, except for a decrease in plasma phosphorus levels in fish fed a 10% ANC diet compared to those fed a 0% ANC diet (P = 0.033). Significant changes were observed in liver metabolism including tricarboxylic acid cycle, amino acid and energy metabolism pathways in fish fed the 20% ANC diet versus the 0% ANC diet (P < 0.05). These results demonstrate that ANC inclusion improved pellet physical quality without impairing feeding behavior and nutritional quality of the fish but inclusion ≥10% in the diet reduced fish growth. This study offers the first comprehensive assessment of the potential of ANC used in fish feed involving feed management, feeding evaluation, and the biological response.

A strain of rainbow trout at the Hagerman Fish Culture Experiment Station has undergone a long-term selection program for growth on a plant-based diet (HGM strain). Comparing fish from the F-8 generation to a commonly available commercial strain selected for growth (CSS), we sought to investigate potential differences in oral tolerance, intestinal microbiota richness and overall growth when fed a 40% SBM diet. Triplicate tanks (initial mean fish weight 77.9 +/- 1.1 g) of each strain were fed diets containing either 0% or 40% SBM over 12 weeks in a factorial design. Fish were weighed every four weeks and subsampled to assess gene expression in the distal intestine. Fish were also sampled at the beginning and end of the study to assess gut histology and characterize intestinal microbiota. At twelve weeks, the HGM strain showed superior growth on both diets (p < .001). Gene expression related to gut health and inflammation show reduced inflammatory response in the HGM fish compared to the CSS strain. Significant effects of strain and diet were also observed on metrics of gut microbiota diversity. Together, these results suggest selection for growth on a plant-based diet also drives selection for increased oral tolerance for dietary soybean meal inclusion.

The current study examines expression of S100 genes, a group of calcium-sensing proteins poorly characterized in fishes. In mammals, these proteins are known to play roles beyond calcium-signaling, including mediation of inflammatory processes. Some S100 proteins also serve as biomarkers for a variety of autoinflammatory conditions. It is well known that salmonids exhibit varying degrees of intestinal enteritis when exposed to alternative feed ingredients containing antinutritional factors, with soybean meal (SBM) being one of the best characterized. The etiology of soy-caused distal enteritis isn't entirely understood but displays similar histopathological alterations to the gut observed in human mucosal inflammatory bowel diseases. We sought to determine if teleost S100 genes show a concomitant response like that observed in mammals, utilizing rainbow trout fed high-soy diets as a model for intestinal inflammation. We examined expression of fourteen known salmonid S100 genes in the liver, first segment of the mid-intestine (proximal intestine), and second segment of the mid-intestine (distal intestine). After 12 weeks on a high-soy diet containing 40% SBM, we observed upregulation of several S100 genes in the distal intestine (S100I2, A10a, V1, V2, and W), no changes in the proximal intestine, and downregulation of S100V2 in the liver. Overall, our results provide further knowledge of the expression of S100 genes and provide targets for future research regarding inflammatory processes in the rainbow trout gut.

Fish oil (FO) sparing is common in aquafeed formulation; however, some alternative lipids have proven to be more successful than others in ensuring adequate growth and maintenance of desirable fillet fatty acid (FA) composition. Depending on the lipids used, grow-out feeds influence the FA composition of the tissues of olean-fleshedo fishes and their responsiveness to subsequent tailoring during finishing. To address whether different lipid sources similarly influence growth performance and tissue composition of a ofat-fleshedo fish, rainbow trout Oncorhynchus mykiss were reared on feeds containing FO or a 50:50 blend of FO and coconut oil (COCONUT), palm oil (PALM), standard soybean oil (STD-SBO), hydrogenated soybean oil (HYD-SBO), low-18:3(n-3) (alpha-linolenic acid) soybean oil (LO-ALA-SBO), or low-18:3(n-3) canola oil (LO-ALA-CAN). Two saturated FA (SFA)-enriched lipids derived from the processing of cottonseed (SFA-COT) or soybean (SFA-SBO) were also evaluated as 50% FO substitutes. After 7 weeks, growth performance was largely unaffected by dietary lipid source. Fillet levels of long-chain (LC) polyunsaturated FAs (PUFAs) among fish that received the HYD-SBO, LO-ALA-SBO, SFA-SBO, and SFA-COT feeds were equivalent to levels in fish that received the FO feed, despite an approximate 50% reduction in dietary LC-PUFA intake. Our results indicate that feeds containing a blend of FO and novel soy- or cottonseed-derived lipids yielded equivalent growth performance and fillet LC-PUFA content in rainbow trout. The use of STD-SBO, COCONUT, PALM, or LO-ALA-CAN did not impair growth or efficiency but did alter the fillet FA profile. Rainbow trout appeared to differ somewhat from other fishes in terms of dietary influence on tissue FA profile; however, the pattern of greater LC-PUFA retention in fish reared on SFA-rich feeds appears to be largely consistent among the fish taxa we have assessed.

Many protein sources, including soybean meal (SBM), have been investigated as alternatives to fish meal (FM) in aquaculture feeds. However, FM replacement in feeds for carnivorous fishes is limited by problems with feed intake, growth rate, and overall health associated with the reduced digestibility of SBM and the antinutritional factors (ANFs) it contains. Processing strategies can reduce the effects of ANFs and can improve protein utilization. We conducted two trials to examine the possibility of further FM replacement in SBM- maximized feeds for hybrid striped bass (white bass Morone chrysops x striped bass M. saxatilis) by using two refined soy products: soy protein concentrate (SPC) and soy protein isolate (SPI). Diets were formulated to maximize FM replacement, beginning with a basal diet containing 10% FM and 65% SBM. Further reductions in FM were made by using SPC or SPI to spare FM- derived protein. Refined soy protein- based feeds were evaluated in feeding trials with juvenile hybrid striped bass that were cultured in recirculating aquaculture systems. Although reducing dietary FM below 10% by using SPC or SPI resulted in decreased production performance, this appears to be due to a reduction in palatability rather than to negative biological effects (e.g., changes in gut histology, major shifts in carcass proximate composition) associated with ANFs or other dietary effects. A moderate reduction in growth associated with administering the SPC- based feeds corresponded with a moderate reduction in feed intake, whereas dietary inclusion of SPI resulted in severe feeding reluctance, starvation, and cannibalism. Although SPC and SPI may vary in their suitability as FM alternatives, the differential performance observedmay also be related to the fact that younger, smaller fish were used in the SPI trial than in the SPC trial. Refined soy proteins can be used in conjunction with SBM to spare FM, but the cost of these products and their acceptability to juvenile carnivorous fish will determine the extent of their utilization in aquafeeds.