The main source of calcium carbonate (CaCO3) in the ocean comes from the shells of calcifying planktonic organisms, but substantial amounts of CaCO3 are also produced in fish intestines. The precipitation of CaCO3 assists fish in intestinal water absorption and aids in whole body Ca2+ homeostasis. Here we report that the product formed in the intestinal lumen of the gilt-head seabream, Sparus aurata, is an amorphous calcium carbonate (ACC) phase. With FTIR spectroscopy and SEM imaging, our study shows that the fish-derived carbonates from S. aurata are maintained as a stable amorphous phase throughout the intestinal tract. Moreover, intestinal deposits contained up to 54 mol% Mg2+, the highest concentration yet reported in biogenic ACC. Mg is most likely responsible for stabilizing this inherently unstable mineral. The fish carbonates also displayed initial rapid dissolution when exposed to seawater, exhibiting a significant increase in carbonate concentration.
Bibliographical noteFunding Information:
We are grateful to the staff of the Interuniversity Institute for Marine Sciences in Eilat for logistic help. Many thanks go to Dr. Angelo Colorni of the National Center for Mariculture, Israel Oceanographic and Limnological Research for invaluable fish health and maintenance advice. We thank Mr Assaf Gal, Weizmann Institute, for his assistance with the ICP-AES analyses, and Dr. Yakov Langzam of Bar Ilan University for assistance with the SEM imaging. This study was supported in part by an Israel Science Foundation grant to MF and by the EU FP-7 MedSeA project, and in part by a German Research Foundation, DIP grant. SW is the incumbent of the Dr. Trude Burchardt Professorial Chair of Structural Biology.