Insect (black soldier fly larvae) oil as a potential substitute for fish or soy oil in the fish meal-based diet of juvenile rainbow trout (Oncorhynchus mykiss).

Alternative sources of fish oil (FO) are one of the major problems in aquaculture; therefore, the goal of the present study was to examine insect (black soldier fly larvae) oil (BSLO) as a potential replacer of fish/soy oil in juvenile rainbow trout (initial average weight of 32 ± 0.15 g) feed. Four diets were formulated wherein FO (control diet) was completely replaced with either soybean oil (SO) or BSLO, and an additional BSLO-based diet supplemented with 1.5% bile acid (BSLO + BA) were fed to the fish for 10 weeks. Growth performance of the BSLO fed group was similar (P > 0.05) to that of the FO and SO fed groups, however, the fish fed BSLO + BA diet registered the lowest growth (P < 0.05). Oil sources did not (P > 0.05) affect the major nutrient content of whole-body, however, the fatty acid composition of the muscle and liver was influenced (P < 0.05), with the highest 14:0, 16:0, and total saturated fatty acid detected in BSLO or BSLO + BA fed trout compared to the others (P < 0.001). No significant differences were observed in eicosapentaenoic acid + docosahexaenoic acid (EPA + DHA) or total n-3 polyunsaturated fatty acid (PUFA) content in muscle among the groups, whereas, the highest EPA:DHA and n-3:n-6 ratios were detected in the FO group. Gene expression for fatty acid binding protein (fabp), fatty acid synthase (fas), and Δ5 desaturase in the liver was lower in FO (P < 0.05), while BSLO + BA registered the highest Δ6 expression (P = 0.006). Supplementation of BA in the BSLO diet increased superoxide dismutase (SOD) and catalase (CAT) activities compared to the other groups (P < 0.05). In conclusion, BSLO could serve as a substitute for FO and SO in rainbow trout diet without negatively impacting growth performance, whole-body composition and nutrient retention, and modulate the expression of fatty acid metabolism-related genes in rainbow trout.

Dietary amino acid supplementation affects temporal expression of amino acid transporters and metabolic genes in selected and commercial strains of rainbow trout (Oncorhynchus mykiss).

Replacement of fishmeal as the major protein source in feeds is critical for continued growth and sustainability of the aquaculture industry. However, numerous studies have shown suboptimal fish growth performance and reduced protein retention efficiency when carnivorous fish species are fed low fishmeal-high plant protein feeds. A study was conducted using a commercial strain and a genetically improved strain of rainbow trout selected for improved performance when fed an all plant protein diet to identify physiological differences associated with growth performance in the selected trout strain. Fifty individuals per strain (average weight ~ 580 g) were force-fed a plant-protein blend with and without amino acid supplementation (lysine, methionine and threonine) at 0.5% body weight and sampled at intervals over 24 h. Samples from intestine and liver were analyzed for specific gene expression analysis related to amino acid transporters, digestive process control, protein degradation and amino acid metabolism. The results showed that expression levels of various intestinal amino acid transporters (SLC1A1, SLC7A9, SLC15A, SLC1A5 SLC6A19 and SLC36A1) were affected by strain, diet and time. Moreover, significant interactions were found regarding the temporal expression levels of cholecystokinin (CCK-L), Krüppel-like factor 15 (KLF15) and aspartate aminotransferase (GOT) transcripts in the examined tissues. The results provide evidence that improved growth and protein retention of the selected strain fed an all-plant protein diet is a result of nutritional adaptation and an overall change in physiological homeostatic control.

Improved performance of a rainbow trout selected strain is associated with protein digestion rates and synchronization of amino acid absorption.

Replacement of fishmeal in feeds is critical for sustainable aquaculture growth. However, replacement with plant protein concentrates reduces fish performance. A rainbow trout strain selected for high performance on a plant protein diet was compared to a non-selected strain to identify physiological mechanisms associated with improved performance. Nutrient digestibility in fishmeal and plant protein diets was assessed and no strain differences were found. Levels of amino acids in the hepatic portal vein and caudal vein were measured at intervals after a single force-feeding of fishmeal, four plant protein concentrates, and a mixture of the concentrates with or without supplementation of three limiting amino acids. Each ingredient affected plasma amino acid levels in a singular manner when fed individually but without predictable additive effects when fed as a mixture. Amino acid supplementation altered uptake and plasma concentrations of all the essential amino acids. The selected trout strain fed the plant protein mixture with amino acids showed a synchronous and homogenous pattern for essential amino acids over time in the hepatic portal vein in contrast to that of the non-selected strain. The results demonstrate that selection favorably altered temporal dynamics of plant protein digestion.

Sex-specific transcriptional responses of the zebrafish (Danio rerio) brain selenoproteome to acute sodium selenite supplementation.

The potential benefits of selenium (Se) supplementation are currently under investigation for prevention of certain cancers and treatment of neurological disorders. However, little is known concerning the response of the brain to increased dietary Se under conditions of Se sufficiency, despite the majority of Se supplementation trials occurring in healthy, Se sufficient subjects. We evaluated the transcriptional response of Se-dependent genes, selenoproteins and the genes necessary for their synthesis (the selenoproteome), in the zebrafish (Danio rerio) brain to supplementation with nutritionally relevant levels of dietary Se (sodium selenite) during conditions of assumed Se sufficiency. We first used a microarray approach to analyze the response of the brain selenoproteome to dietary Se supplementation for 14 days and then assessed the immediacy and time-scale transcriptional response of the brain selenoproteome to 1, 7, and 14 days of Se supplementation by quantitative real-time PCR (qRT-PCR). The microarray approach did not indicate large-scale influences of Se on the brain transcriptome as a whole or the selenoproteome specifically; only one nonselenoproteome gene (si:ch73-44m9.2) was significantly differentially expressed. Our qRT-PCR results, however, indicate that increases of dietary Se cause small, but significant transcriptional changes within the brain selenoproteome, even after only 1 day of supplementation. These responses were dynamic over a short period of supplementation in a manner highly dependent on sex and the duration of Se supplementation. In nutritional intervention studies, it may be necessary to utilize methods such as qRT-PCR, which allow larger sample sizes, for detecting subtle transcriptional changes in the brain.

Zebrafish (Danio rerio) vary by strain and sex in their behavioral and transcriptional responses to selenium supplementation.

We used the Nadia, Gaighatta, Scientific Hatcheries, and TM1 zebrafish (Danio rerio) strains to test the hypothesis that variation among populations influences the behavioral and transcriptional responses to selenium supplementation. When fed a diet with control levels of selenium, zebrafish strains differed significantly in behavior, characterized as their mean horizontal and vertical swimming positions within the tank. The four strains also differed in brain expression of selenoprotein P1a (sepp1a), glutathione peroxidase 3 (gpx3), thioredoxin reductase 1 (txnrd1), and tRNA selenocysteine associated protein 1 (secp43). Iodothyronine deiodinase 2 (dio2) did not differ among strains but showed a sex-specific expression pattern. When supplemented with selenium, all strains spent a greater proportion of time near the front of the tank, but the response of vertical swimming depth varied by strain. Selenium supplementation also caused changes in selenoprotein expression in the brain that varied by strain for sepp1a, secp43, and dio2, and varied by strain and sex for txnrd1. Expression of gpx3 was unaffected by selenium. Our data indicate that selenium homeostasis in the brain may be a regulator of behavior in zebrafish, and the strain-specific effects of selenium supplementation suggest that genetic heterogeneity among populations can influence the results of selenium supplementation studies.

Effects of dietary selenomethionine on cutthroat trout (Oncorhynchus clarki bouvieri) growth and reproductive performance over a life cycle.

A 2.5-year feeding trial was conducted in which cutthroat trout (Oncorhynchus clarki bouvieri) were fed either a basal diet (1.2 microg Se/g diet) or the basal diet supplemented with 2, 4, 6, 8, or 10 microg Se/g diet as selenomethionine from 1 g weight to maturation [corrected]. After 44 weeks of feeding, a subsample of fish was removed from dietary treatment groups and fed the basal diet for an additional 32 weeks. Concentrations of Se in whole fish and eggs increased in proportion to dietary Se intake, but no differences in growth, feed intake, survival, or egg hatchability were observed among dietary groups. Cranial-facial deformities in second-generation offspring were less than 6% in all treatment groups except for fish fed the diet supplemented with 4 microg Se/g diet as selenomethionine [corrected], where a 9.2% incidence was observed. Fish switched from selenomethionine-supplemented diets to the basal diet lost Se, calculated as microg Se lost/g weight gain, at 1.01, 2.84, 4.42, and 4.42 for dietary treatment groups 3, 4, 5, and 6, respectively. Results suggest no toxicity of dietary selenomethionine up to 10 microg/g supplemented diet and that with total life-cycle exposure, cutthroat trout increase Se excretion to maintain whole-body concentrations below toxic levels.