Trace minerals, such as Zn, Mn, Cu, Fe, Se and Cr, are essential for proper development of bone, muscle, nervous, and reproductive systems. Moreover, in aquatic species, as in terrestrial animals, minerals such as Zn and Cu play a critical role in the production and maintenance of epithelial tissue – as the first line o f defense against microbes . Alongside Mn, Zn and Cu are of the ut most importance in wound healing, increasing the speed of the re-epithelialization processes in fish . M etal-amino acid complexes (Zinpro Performance Minerals) have proven to be more efficient than inorganic minerals in reducing skin lesions of Atlantic salmon infestated with Caligus, and by increasing antioxidant capacity (i.e. GPx ) and barrier defenses (i.e. goblet cells in skin and intestine) in European seabass. Supplementation with Zn also increased the activity of digestive enzymes, and intestinal villi height and integrity in Nile tilapia. In channel catfish, Zn-AA complex proved to be at least 3 times more effective than ZnSO4 in meeting growth requirements in both purified and practical diets containing phytic acid, and in protecting fish against Edwardsiella ictalurid . Chromium supplementation proved to be equally as important in the modulation of the immune system, reducing cortisol and oxidative stress, and improving glucose metabolism, through the activation and modulation of insulin production and signaling pathway. The positive effect of Cr on growth has been shown in several fish species, such as tilapia (hybrid, Nile, red) and carp (grass, common, mirror). Cui et al. (2018) evaluated the growth response of common carp to Cr-DL-methionine (Availa® Cr) supplementation and estimated the optimal dietary Cr3+ to be 1.09 ppm. Supplementation of juvenile Nile tilapia diets with 0.5 ppm Cr, as Availa® Cr, improved final body weight and feed conversion ratio by 8 and 14%, respectively. In the same study, supplementation with 0.3 ppm Se, as Availa® Se, numerically improved final body weight and FCR by 7 and 11.4%, respectively. Highest final body weight and lowest FCR were found with the combination of 0.5 ppm Cr and 0.3 ppm Se from Zinpro Performance Minerals. Chromium supplementation in fish has shown beneficial effects related to immunological status, and metabolism of proteins, carbohydrates, lipids, and nucleic acids. Furthermore, supplementation with Zn and Cr combined seems to have a synergistic effect in controlling glycemia, thus improving carbohydrate utilization. Considering that most aquatic species, included most farmed fish, are poor users of carbohydrates as an energy source, supplementation with Cr and Zn constitutes an interesting strategy to enhance glucose utilization in order to spare dietary protein for muscle growth, increasing fillet and carcass yield. In addition, this protein sparing effect may help the aquaculture industry reduce feed costs through the utilization of cheaper dietary energy sources, such as carbohydrates.