Fish are able to maintain their extracellular [Ca2+] relatively constant through regulatory mechanisms that control the influx or efflux of Ca2+ in osmoregulatory organs. To understand in depth the molecular basis of these adjustments, the whole gill transcriptome of the euryhaline teleost Tetraodon nigroviridis exposed to high and low [Ca2+] was obtained using Super Serial Analysis of Gene Expression (SuperSAGE).