Investigation of the effects of dietary protein source on copper and zinc bioavailability in fishmeal and plant-based diets for rainbow trout

•Plant-based diets require higher Cu and Zn supplementation to maximize trout growth.•No antagonism between Cu and Zn was observed in rainbow trout fed plant-based diets.•Cu concentration but not source alters growth and tissue minerals in rainbow trout.

Limited research has examined the effects that dietary protein sources have on copper (Cu) and zinc (Zn) absorption, interactions and utilization in rainbow trout. Therefore, the objective of the first trial was to determine what effect Cu source (complex vs. inorganic) and Cu concentration (0, 5, 10, 15, 20 ppm) had on rate and efficiency of gain and Cu tissue concentration in rainbow trout fed both plant-protein and animal-protein based diets. The second trial then examined if interactions occur due to increasing dietary content of Zn (0, 30, 300, 1500 ppm) in rainbow trout fed a plant-based diet. Results from the first trial demonstrated differences in growth and tissue mineral concentrations due to Cu concentration but not source. Trout fed plant-based diets had higher weight gain, improved feed conversion ratio and higher hepatic Cu concentration when compared to fishmeal-fed trout. Results from the second trial show that increasing dietary Zn supplementation increased whole body Zn and Cu at 12 weeks. No significant antagonism between Cu and Zn was observed in rainbow trout fed plant-based diets. Zn deficiency signs were observed at 12 weeks in trout fed a plant-based diet without Cu and Zn supplementation which included mortality, cataracts and caudal fin erosion. Results of these studies indicate that rainbow trout fed plant-based diets require both Cu and Zn supplementation at concentrations higher than those previously reported to maximize growth.