The significance of river runoff in shaping the current distribution of freshwater fish on the Kamchatka Peninsula

This article addresses the perceived tolerance of typical freshwater fish species to salinity and the possibility of their dispersal through marine/ocean waters. Based on the results of long-term studies of fish ecology in the estuaries and coastal zone of the Kamchatka Region, the hypothesis of the crucial role of river runoff in the modern zoogeography of freshwater ichthyofauna on the Kamchatka Peninsula is discussed. The data suggests that many resident freshwater fishes of Kamchatka are capable of tolerating elevated salinity levels much better than previously thought, which is possibly related to their evolution, first of all, their freshwater or marine origin. Therefore, these fish are capable of spreading from one river system to another via river mouths and adjacent coastal areas. This method of dispersal is most likely to occur within the coastal zone significantly affected by high river runoff where extensive areas of low salinity exist. These findings should be considered when examining the occurrence and biogeographical distribution of typical freshwater fish species.