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There is a growing demand within research and conservation hatcheries to rear fish that more closely approximate the smaller size and leaner body composition of their wild counterparts. Low-lipid diets may help achieve this goal as they can provide all the nutritional needs of young fish and can lead to slower growth and leaner bodies. We compared growth of Chinook Salmon Oncorhynchus tshawytscha fed three experimental low-lipid diets (11–12, 8–9, 4–6% lipid) at the onset of feeding with a commercially available high-lipid diet (18–20%) and an experimentally formulated high-lipid control (13.9% lipid). After 5 mo on their respective treatments, the size, growth rate, and daily growth index of fish on the commercial diet were significantly higher than those on the three low-lipid diets. We also compared whole-body lipid content across our five diet treatments. Whole-body lipid content was significantly different across the five diets, with fish fed the commercial diet having, on average, an almost twofold higher lipid content over fish fed the lowest lipid diet formulation. We present comparable data from a limited sample of wild juvenile conspecifics as observations. We suggest that low-lipid starter diets can be used to produce healthy fish that more likely emulate some of the variations in size and body composition of wild fish. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Sturgeon culture has developed greatly since the 1980s. Cultured sturgeon are often fed a commercial salmonid feed high in fish meal (FM). However, economic and sustainability concerns have put pressure on aquafeed manufactures to incorporate alternative proteins such as soybean meal (SBM). This experiment investigates dietary SBM sensitivity in shovelnose sturgeon (Scaphirhynchus platorhynchus). Diets were formulated to contain 0%, 17%, 34%, and 51% SBM and fed for 8 weeks. Weight gain, specific growth rate (SGR), feed efficiency (FE), body and liver composition, and intestinal histology were determined. Although sturgeon growth rates were low for all diets, weight gain in fish fed the diet with 17% SBM averaged 55.6% of sturgeon fed the fish meal-based control diets. Statistically lower negative growth and FE (P < 0.05) were observed when SBM was included at 51% of the diet. However, whole-body proximate composition and hepatic lipid and glycogen content were not altered by dietary SBM inclusion level, and histological evaluation of the distal intestine was inconclusive. These results provide preliminary insight into the effect of diets containing high levels of SBM on growth and health of Scaphirhynchus sturgeon. [ABSTRACT FROM AUTHOR]

This study examined the effects of elevated temperature and dietary Thermal Care, Bio-Mos and GroBiotic A on production performance and blood chemistry parameters in rainbow trout (Oncorhynchus mykiss). Rainbow trout under supraoptimal thermal conditions (18 °C) exhibited increased growth and feed intake but no change in feed efficiency for 6 weeks. This suggests that rearing fish at 18 °C may enhance production performance during the early stages of the grow-out process. By 12 weeks, fish at 18 °C showed increased feed intake, decreased feed efficiency, but no change in growth. Additionally, fish at 18 °C had lower protein content, protein retention efficiency, and energy retention efficiency. Elevated temperature did not change relative maximum swimming speed but did increase hematological parameters, thereby increasing the fish's oxygen supply capacity. There was preliminary evidence that Thermal Care improved rainbow trout growth under optimal thermal conditions (15 °C). However, fish fed Thermal Care at 18 °C exhibited increased feed intake but one of the lowest final fish weights leading to the lowest feed efficiency. Additionally, Grobiotic A impacted acid-base balance through changes in blood pH, TCO 2 , and HCO 3 − although the relevance of these interactions remains to be determined. By the end of the experiment, there were no noticeable benefits of including Thermal Care or Bio-Mos or GroBiotic A on production performance at either culture temperature. • Temperature had a large impact on rainbow trout performance. • 18 °C enhanced production during early grow out of trout. • Prolonged exposure to 18 °C resulted in negative effects on trout production. • Additives did not improve thermal tolerance. • Thermal Care may improve growth at 15 °C. [ABSTRACT FROM AUTHOR]

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. • Selection for growth on a plant-based diet confers improved oral tolerance to soybean meal inclusion in rainbow trout diets. • Growth of selected rainbow trout was greater than non-selected rainbow trout fed plant-based or fishmeal-based diets. • Ohnologues of IL -17A/F2 were first to respond in rainbow trout fed diets containing 40% soybean meal. [ABSTRACT FROM AUTHOR]