Complexes of t rivalent chromium (Cr3+ ) with organic acids and amino acids have been shown to play a key role in carbohydrate, protein and lipid metabolism. A lthough not completely understood, improved utilization and regulation of carbohydrates (glucose) by Cr3+ associates with increased insulin sensitivity , activation of intracellular insulin signaling, and glucose transporter translocation into the cell membrane. Dietary supplementation with Cr methionine (Cr-Met) complex proved to be consistently effective in improving feed utilization in crustaceans and fish, regardless of their trophic level (from carnivorous to omnivorous species), optimum temperature (warm- t o cold-water species) or salinity tolerance (seawater to freshwater).
The efficacy of graded dietary levels of Cr-Met complex, in the form of Availa®Cr 1000, was recently evaluated in terms of performance and whole-body nutrient retention in Atlantic salmon ( Salmo salar ). The trial was comprised of four dietary treatments: a control diet (Control) without Cr-Met complex supplementation; and three other diets, based on the Control formulation, but supplemented with Cr-Met complex at increasing doses (0.2 , 0.4 and 0.6 mg.kg-1) . Quadruplicate groups of 25 Atlantic salmon, with a mean initial body weight of 57.1 ± 3.2 g were fed one of the four experimental diets during 95 days. At the end of the trial, the final body weight ranged between 239.6 and 253.6 g . Specific growth rate varied between 1.51 and 1.57 %/ day. When compared to Control, supplementation with Cr-Met complex at 0.2 and 0.4 mg.kg-1 resulted in significant improvements for weight gain and feed utilization (FCR and PER). Moreover, s upplementation with Cr-Met complex at only 0.2 mg.kg-1 significantly increased protein ( by 6.8%) and phosphorus ( by 13.2%) retention (% nutrient intake). The positive effect of Cr-Met complex shown in performance and nutrient retention seems to be associated with a better utilization of glucose as an energy source, which allows for protein to be spared for growth purposes. Supplementation with Cr-Met complex has significantly increased the activity of glucokinase and glycogen content in liver of salmon, which is in agreement with the effect shown by Cr-Met complex in the glucose metabolism of other fish and shrimp species . These results indicate that supplementation with Cr-Met complex at doses as low as 0.2 mg .kg -1 can be an efficient strategy to improve performance, while reducing excretion of nitrogen and phosphorus into to the environment, contributing therefore, to the sustainability of Atlantic salmon production.