The composition and organisation of extracellular matrix (ECM)-related molecules change during development. These components interact with different cell surface receptors to modulate the transduction of signals for cell growth, differentiation, migration, proliferation and apoptosis. Previous findings in the teleost fish gilthead seabream (Sparus aurata L., Teleostei), a marine protandrous hermaphrodite fish, showed that endocrine and immune stimuli are able to modulate the expression of ECM-related molecules, as well as specific correlations between them. In the present study, quantitative reverse transcription–polymerase chain reaction was used to examine the gene expression profile of ß1 integrin isoform b (ITGB1b) and its possible role in reproductive physiology, especially in relation to spermatogenesis. Expression profiles were analysed in the context of the reproductive cycle (RC) and in relation with other ECM-related molecules, including matrix metalloproteinase (MMP)-2, MMP-9, MMP-13, tissue-specific inhibitor of metalloproteinase (TIMP)-2a, TIMP-2b, collagen (COL1A1) and ITGB1a. Expression of ITGB1b was found in the testis and brain and, to some extent, in endothelial cells. In contrast, ITGB1a was expressed ubiquitously. In the testis, the ITGB1b expression peaked during spermatogenesis, whereas the expression of the other ECM-related molecules is induced mainly during the post-spawning stage, both stages of marked tissue remodelling during the first and second RC in males. In addition, in fish exposed to the endocrine disruptor 17a-ethynyloestradiol (at 5 and 50 µg g–1 food during 7, 14 and 21 days), ITGB1b expression in the testis was inhibited in a dose- and time-dependent manner and was related to reduced serum levels of testosterone. Together, these results suggest a different functionality for the two ITGB1 isoforms in the gilthead seabream, where ITGB1b is more specifically involved in reproduction. This is the first report of an ITGB1 gene isoform whose expression is restricted to endocrine-related tissues in vertebrates.