<p>Artificial infrastructure alters marine habitats, community and ecosystem structure and provides footholds for invasive species. Thus far, most research has focussed on the abundance and diversity of taxa associated with artificial structures with little emphasis on the fitness and health of the species that reside on them. This study examined several fitness and health proxies (hepato-somatic index (HSI), Fulton’s index and parasitic load) of two small, benthic fish species—the native <i>Trinorfolkia clarkei</i> (sampled at one site) and the introduced <i>Forsterygion varium</i> (sampled at three sites)—inhabiting two distinct habitat types: common coastal artificial structures (i.e. piers and marinas) and adjacent natural reefs, in south-eastern Tasmania (Lutruwita), Australia. There were no significant differences in fitness proxies between natural and artificial habitats for <i>F. varium</i>. The native <i>T. clarkei</i> exhibited a significantly higher HSI on a natural reef than on an artificial structure; however, it showed no differences in Fulton’s index between habitats. The results indicate that individual fitness is species-, location- and habitat type-specific. Understanding how artificial infrastructure can impact the health of native and introduced species is necessary for effective management of marine systems. This study is the first to investigate the difference in the impacts of artificial structures on the fitness of native and introduced fish species, highlighting the urgent need for further research to address this significant knowledge gap.</p>