Herbivory has long been considered an important component of biotic resistance against macroalgae invasions in marine habitats. However, most of the studies on herbivory of invasive algae refer only to consumption by strictly herbivorous organisms, whereas consumption by omnivorous organisms has been largely ignored and rarely quantified. In this study, we assess whether the commonest omnivorous sparid species in the Mediterranean Sea are consuming the highly invasive alga, Caulerpa cylindracea, and determine its importance in their diet and their electivity towards it as a source of food. Our results confirm that three of the four fish species we studied do, in fact, consume C. cylindracea, but in most cases, the importance of C. cylindracea in the diet was low. Indeed, the low electivity values confirm that all four fish species avoid feeding on the invasive alga and that it is probably consumed accidentally. However, despite animals and detritus being the main food for these sea bream species, several individual specimens were found to have consumed high amounts of C. cylindracea. This suggests a potential role that these fish species may play in controlling, to some extent, the abundance of the invader. We suggest that herbivory by omnivorous fish might complement the higher impact exerted by the strict herbivores, and together, they might contribute to the overall biotic resistance against the invader.