Availability of supplemental amino acid-chelated trace elements in diets containing tricalcium phosphate and phytate to rainbow trout, Oncorhynchus mykiss

This study investigated the availability of amino acid-chelated trace elements to rainbow trout fed diets containing tricalcium phosphate (TCP) and phytate (PH) that are known mineral inhibitors. Six semi-purified diets were supplemented with trace elements either from the sulfate (SF, diets 1 and 2) or amino acid-chelate (AM, diets 3-6). Diets 1 (SF) and 3 (AM) contained neither TCP nor PH. Diet 4 (AMPO) included TCP while Diet 5 (AMPH) contained PH alone. Diets 2 (SF++) and 6 (AM++), on the other hand, contained both inhibitors, Rainbow trout weighing 1.6 g were fed the experimental diets three times daily to near satiation for 18 weeks. Growth, whole body mineral deposition, and enzyme activity/expression were measured after the trial. Growth of fish fed the SF++ diet was significantly lower than the rest of the groups. Whole body Cu content was significantly higher in AM groups than in SF groups with or without TCP and PH. Whole body and bone Zn contents were significantly higher in fish fed the diet containing AM alone compared to the rest. Alkaline phosphatase activity was significantly higher in fish fed the diet containing AM alone than with fish fed the SF diet with or without TCP and PH. CuZnSOD and DNA polymerase were highly expressed in the AM compared to the SF groups. The results show that availability of trace elements is significantly affected by their chemical form and that amino acid-chelates are more beneficial for rainbow trout even in, the presence of TCP and PH compared to the inorganic sources tested. (C) 2003 Elsevier Science B.V. All rights reserved.