Product knowledge has been recognised as an important factor influencing consumer decision making. The aim of this study was to assess Spanish consumers’ knowledge about fish as well as their relationship with certain socio-demographic characteristics. Objective and subjective knowledge were measured by means of 5 and 4 items respectively. Overall results revealed the existence of a certain lack of knowledge about fish, although some differences were observed depending on gender, age, education level, region of residence and growing up region (coastal or interior). A positive relationship between objective and subjective knowledge was also detected.