Fish scales are collagen based structures that display interesting mechanical properties, particularly in the wet state. In this paper we study the effect of water content on the thermal transitions of scales from the Amazonian fish Arapaima Gigas by means of Differential Scanning Calorimeter (DSC) tests. The endothermic peaks found are discussed and the results are compared with previous studies of other collagen based structures. The peaks observed were found to depend on the water content of the samples. The role of water on the thermal stability of fish scales is discussed. The peak temperature related to the denaturation of collagen was found to increase with increasing water content. Hence, samples with higher water content were more thermally stable than samples with lower water content. This tendency is contradictory with regard to that observed on other collagen based structures such as bones and tendons. © 2012 Elsevier B.V.