Conclusions about the absence of any persistent long-term changes at the population level in planktonic biota after pelagic oil spills are fully valid in relation to fish populations. Due to oil localization within the surface layer of seawater, the mortality of water column organisms, including pelagic fish, is practically excluded. Fish mass mortality has never been observed even after catastrophic oil spills in the open sea. Available publications on the subject suggest that adult fish are capable of detecting and avoiding zones of heavy oil pollution.
An adverse impact of oil spills on fish is most likely to be observed in the shallow coastal areas of the sea where the water dynamics are slow. Fish in early life stages are known to be more vulnerable to oil, compared to adults, and, therefore, some younger fish may be killed by exposure to high concentrations of toxic components of crude oil. However, calculations and direct observations indicate that such losses could not be reliably detected against the natural background of high and variable mortality at embryonic and postembryonic stages of fish development.