Oxidative stress-related gene expression in diploid and triploid Rainbow Trout (Oncorhynchus mykiss) fed diets with organic and inorganic zinc

Authors: MEILER, KRISTEN - University Of Idaho; Cleveland, Beth; Radler, Lisa; KUMAR, VIKAS - University Of Idaho

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2020
Publication Date: 11/13/2020
Citation: Meiler, K., Cleveland, B.M., Radler, L.M., Kumar, V. 2020. Oxidative stress-related gene expression in diploid and triploid Rainbow Trout (Oncorhynchus mykiss) fed diets with organic and inorganic zinc. Aquaculture. 533: 736149. https://doi.org/10.1016/j.aquaculture.2020.736149.
DOI: https://doi.org/10.1016/j.aquaculture.2020.736149

Interpretive Summary: Zinc in an essential micronutrient critical for growth, bone mineralization, and antioxidant defenses. In rainbow trout, there is a dietary requirement for optimal growth performance, but it is unknown if levels beyond that affects fish health, or if organic versus inorganic zinc affects affects that response. Rainbow trout are also commonly produced as both diploids and triploids, but it has not been determined if these groups respond differently to dietary zinc supplementation. In this study diploid and triploid rainbow trout were fed diets with increasing levels of zinc in either the organic or inorganic form and expression of antioxidant-related genes were analyzed. Most genes demonstrated a dose-dependent expression response, suggesting that increasing levels of dietary zinc provide a antioxidant health benefit, particularly during supplementation with organic zinc. Triploids were more susceptible to dietary zinc, suggesting they may have a higher zinc requirement than diploids. In summary, these findings support that dietary supplementation of organic zinc beyond that required for optimal growth provide added health benefits, particularly during periods of increased oxidative stress.

Technical Abstract: In rainbow trout, zinc is among the most important essential micro-minerals involved in many biological processes such as oxidative stress, bone mineralization, and growth. Organic minerals are often reported to be more bioavailable to fish, thus requiring lower amounts to meet the zinc requirement. Rainbow trout are commonly reared as both diploids and triploids, but it is unknown if ploidy status affects how the fish responds to dietary zinc supplementation. This study examined gene expression response patterns in both diploid and triploid rainbow trout fed to satiation for 9 weeks with either inorganic (ZnSO4) or organic (amino acid chelated) zinc supplemented in incremental levels (Zn63, Zn123, Zn183) to an otherwise sufficient basal diet (Zn33). Hepatic expression of genes related to oxidative stress were analyzed and included superoxide dismutase (SOD1; SOD2), glutathione peroxidase (GPX1a; GPX1b1; GPX1b2), catalase (CAT), glutathione reductase (GSR), glutathione S-transferase (GST), liver X receptor (LXR), and the zinc storage protein, metallothionein-A (MTA).Expression of all genes, except MTA, was elevated with organic zinc supplementation. There was also a zinc dose-dependent increase in SOD1 and SOD2 expression (organic zinc only) and CAT expression. Dose-dependent reductions in gene expression were detected for GSR, GST, and MTA. There were also gene expression differences between diploids and triploids, suggesting that triploids were more sensitive to potential improvements in zinc bioavailability in the organic zinc-containing diets. Findings support that zinc supplementation, particularly organic zinc, beyond the dietary requirement enhances the antioxidant defense system that may improve fish health by reducing oxidative stress.