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Why some rainbow trout genotypes grow better with a complete plant-based diet? A transcriptomic and physiological analyses on three isogenic lines

ABSTRACT: We have investigated the mechanisms behind the response to a plant based diet over a long term period by comparing the transcriptome of 3 isogenic lines (R23h, AB1h, A22h) of rainbow trout. These families represent an interesting genetic materiel to work on as they have similar responses when fed marine based-diet (M diet) but highly different responses when fed a plant-based diet (V diet). Fish were fed since 1st feeding with either a plant-based diet, or a marine diet (ad libitum (M diet) or restricted (MR)). We showed that differences in the ability to grow with the V diet observed amongst genotypes was not due to higher feed intake, but to higher feed efficiencies. The comparison of transcriptome profiles revealed 575, 1770 and 2973 probes differentially expressed amongst the three genotypes when fed the V diet. Interestingly, genotypes which were the less affected by the V diet had exhibited the highest growth. These results demonstrated that those fish were able to maintain energy production and protein synthesis. Moreover, those genotypes were also able to activate pathways linked to lipid and cholesterol metabolism, such as the biosynthesis of omega 3 LC-PUFA. Finally, as it has already been demonstrated, immunity seems also to play an important role in the ability of fish to use the V diet, and further investigations are needed to understand by which ways immunity interacts with growth.

ORGANISM(S): Oncorhynchus mykiss

PROVIDER: GSE179672 | GEO | 2021/08/16

REPOSITORIES: GEO

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Project description:Sustainable aquaculture, which entails proportional replacement of fish-based feed sources by plant-based ingredients, is impeded by the poor growth response frequently seen in fish fed high levels of plant ingredients. To evaluate the potential to improve, by means of early nutritional exposure, the growth of fish fed plant-based feed, rainbow trout swim-up fry were fed for 3 weeks either a plant-based diet (diet V, V-fish) or a diet containing fishmeal and fish oil as protein and fat source (diet M, M-fish). After this 3-week nutritional history period, all V- or M-fish received diet M for a 7-month intermediate growth phase. Both groups were then challenged by feeding diet V for 25 days during which voluntary feed intake, growth, and nutrient utilization were monitored (V-challenge). The results of the V-challenge showed a higher growth rate and higher feed intake in fish of nutritional history V compared to M (see PMID:24386155). To identify the molecular mechanisms that govern the enhancement of feed acceptance following early-feed exposure of diet V, we performed microarray expression analysis using swim-up fry collected at the end of early-feeding exposure (diet M and diet V), as well as brain and liver of juveniles sampled at the end of the V-challenge (M-his and V-his), and employing a rainbow trout microarray platform with 8 X 60K probes per slide. Persistently differentially expressed genes were identified by isolating probes that were differentially expressed (fold change ≥ 1.5 and p {nutritional history} ≤ 0.05), both at the end of the early exposure, and in either brain or liver of juvenile trout at the end of the V-challenge. Overall, 1787 (3-week + Brain) and 924 (3-week + Liver) mRNA probes were found to be persistently affected by nutritional history of early-feeding exposure. This positive response is encouraging as a potential strategy to improve the use of plant-based feed in fish, of interest in the field of fish farming and animal nutrition in general. Furthermore, the genes associated with mediating this positive early feeding effect, could serve as potential biomarkers to evaluate increasing acceptability of plant-based diets in fish farming.

Project description:Current commercially available feeds for salmon are predominantly made of plant ingredients, with consequent changes to the composition and contents of a range of nutrients and other components in the diet. There are concerns that, with these major changes in raw materials, new feeds will affect not only the composition and contents of nutrients, but also the bioavailability and, combined with the limited knowledge of micronutrient requirements for Atlantic salmon, this might impact growth performance and health of the fish. The present study investigated the effects of graded levels of a micronutrient package supplemented to feeds formulated with low levels of marine ingredients and fed to diploid and triploid Atlantic salmon throughout the freshwater phase. Specifically, fish were fed three diets containing low levels of FM and FO and identical in formulation other than being supplemented with 3 levels (L1, 100 %; L2, 200 % and L3, 400 %) of a micronutrient mix formulated as a modification of current nutrient levels reported for salmon. Duplicate groups of diploid and triploid parr were fed the experimental diets from around 30 g to seawater transfer and the effects on growth performance, feed efficiency, biochemical composition, liver histology, hepatic gene expression (transcriptome) and smoltification efficiency determined. Microarray analysis revealed that the hepatic transcriptome profile of diploid fish fed diet L2 was more similar to that observed in triploids fed diet L3 than to those fed L2, suggesting that micronutrient requirements of triploid salmon may differ from levels accepted in diploid salmon. Different levels of micronutrient supplementation affected the expression of key genes involved in lipid metabolism. In particular sterol biosynthesis pathways (steroid and terpenoid backbone synthesis) were down-regulated in both L2-fed diploids and L3-fed triploids when compared with diet L1-fed diploids and triploids, respectively. Gene sets analysis showed an up-regulation of genes involved in immune processes in triploid salmon fed diet L3. Another biological category affected by diet in triploid salmon was genetic information processing. In fish fed diet L3 down-regulation of RNA degradation, proteasome, RNA polymerase, spliceosome and ribosome was observed, suggesting a decrease in protein turnover in this group, which may indicate a decrease in energy expenditure. In addition, one-carbon metabolism was affected by diet in diploid and triploid salmon.

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Why some rainbow trout genotypes grow better with a complete plant-based diet? A transcriptomic and physiological analyses on three isogenic lines

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