Heating otoliths of the orange roughy(Hoplostethus atlanticus;Trachichthyidae) by the break‐and‐burn method causes a crystal transformation from aragonite to calcite. However, the change does not affect the legibility of the check rings. Orange roughy otolith check rings fall into two classes: a diffuse deposit (that is not visible in the break‐and‐burn method, but may have an annual periodicity) and structural check rings (which appear as fine lines on the surface, but as dark bands in the body of the otolith). Structural check ring deposition is irregular, but fortuitous aggregations of structural check rings might be mistaken for conventional annual check rings.