GENE EXPRESSION PATTERNS IN DIPLOID AND TRIPLOID RAINBOW TROUT Oncorhynchus mykiss FED DIETS WITH ORGANIC OR INORGANIC ZINC

In rainbow trout, zinc is among the most important essential micro-minerals involved in many biological processes.  Zinc plays a role in oxidative stress, bone mineralization, and growth.  The bioavailability of zinc depends largely on feed ingredients and their compositions. Plasticity of transition metals, such as zinc, is due in part to their ability to form complexes with nutrients in feed. O rganic minerals have been observed to be more bioavailable to fish, resulting in a reduction in the amount required to be effective. This study examined gene expression  response  patterns in both diploid and triploid rainbow trout fed to satiation for 9 weeks with inclusion of either inorganic (ZnSO₄ ) or organic (Alltech) zinc in incremental levels (Zn₆₃, Zn₁₂₃, Zn₁₈₃ ) to an otherwise sufficient basal diet (Zn₃₃) . Hepatic genes  related to oxidative stress were analyzed and included superoxide dismutase (SOD1; SOD2), glutathione peroxidase (GPX1a; GPX1b1; GPX1b2), catalase (CAT), glucocorticoid receptor (GR), glutathione S-transferase (GST), liver X Receptor (LXR), and the zinc storage protein,  metallothionein-A (MTA).

Results from this study revealed that genes related to oxidative stress  were  regulated by ploidy level and the dosage and type of zinc (Table 1). Organic zinc promoted higher levels of gene expression and increased susceptibility to a dose effect, supporting that organic zinc exhibits better bioavailability. Additionally, gene expression was more responsive to organic zinc in triploids  than in diploids, suggesting that diploid and triploid trout have different zinc requirements. Based on these results, o rganic zinc appears to be more available, thus fish are more sensitive to it and  should require less to meet the dietary zinc requirement. These findings also establish a relationship between dietary zinc and oxidative stress defense, indicating that adequate levels of dietary zinc are important for  both fish health and growth performance .