Holocene otoliths reveal recent body size increase in a non-commercial fish species

Declines in body size are considered a common response of marine ectotherms to global warming, yet evidence remains inconsistent and is scarce for non-commercial species. Moreover, the lack of pristine, pre-industrial baselines limits our ability to assess whether modern changes exceed natural variability. Here, we reconstruct growth, lifespan and body-size variation in the non-commercial black goby, Gobius niger, over the last 8,000 years in the northern Adriatic Sea, using morphometric measurements and sclerochronological age estimates from radiocarbon-dated fossil and modern otoliths. Holocene black gobies maintained remarkably stable body size over millennial timescales. In contrast, modern black gobies grow faster and reach larger size-at-age, with the strongest differences observed in the first year of life. Because recent warming in the northern Adriatic Sea coincides with major anthropogenic environmental disturbances, the observed size increase is unlikely to reflect temperature alone, it is more plausibly linked to interacting climatic and ecological drivers, including altered trophic interactions and reduced mortality rates. As demersal generalists with broad ecological tolerance, black gobies can sustain or even enhance their growth under conditions that limit more specialised or active species. Our findings highlight the value of otolith archives for establishing long-term biological baselines.