Changes in fish health and local fish communities in eelgrass meadows following a bunker oil spill in the Baltic Sea

This is the authors' abstract. We don't add key points for this paper.

spill of heavy bunker oil. In summer 2024, we also collected fish samples for histopathological analyses and polycyclic aromatic hydrocarbons (PAH) in eelpout (Zoarces viviparus) and three-spined sticklebacks (Gasterosteus aculeatus; PAH only) across three sites with varying levels of oil contamination to assess individual fish health. Our results indicate lowest PAH-concentration in fish from the least oil contaminated site, but PAH-levels were generally low, < 23 μg/kg wet weight. All examined eelpouts exhibited only minor gill and liver tissue alterations, including those from the reference site, suggesting that the observed alterations were not a result of oil exposure. At the fish community level, there was a clear shift from eelpout to sticklebacks in oil contaminated sites in 2024, although eelpout abundance increased again in 2025. In conclusion, while the oil spill may have resulted in somewhat elevated PAH-concentration in fish, this had no marked histological impact on fish health. Still, there was a clear shift in fish community composition in the summer following the oil spill, but abundances were back to 2022 levels within two years after the accident.