Limnology and Oceanography
Marine teleostean fish are hypo-osmotic to seawater. As part of a multiorgan osmoregulatory strategy they drink seawater and selectively absorb water and minerals across the intestinal epithelium. Notably, divalent cations (Ca2+ and Mg2-) are left behind. We report here that in the gulf toadfish, Opsanus beta, the ionic by-products of osmoregulation in the intestine contribute to de novo formation of a carbonate mineral, tentatively identified as calcian kutnohorite. Our data suggest that intestinal mineralization is a general feature of osmoregulation in marine teleosts and that this process is an unrecognized and possibly substantial source of marine carbonate sediments.
Patrick J. Walsh, Patricia Blackwelder, Kenneth A. Gill, Eva Danulat, and Thomas P. Mommsen. 1991. Carbonate Deposits in Marine Fish Intestines: A New Source of Biomineralization .Limnology and Oceanography , (6) : 1227 -1232. https://nsuworks.nova.edu/occ_facarticles/761.