Marine identification key: Fish


There are several fish species that are considered invasive in Nordic waters or part thereof.

This key focuses on marine species. However, several freshwater species are able to form self-sustaining populations in brakish water (e.g. The Baltic Sea) and thus will also be included here.

For feature information about coastal fish in the Baltic Sea see HELCOM report.

The following species will also be included in the key:

  • Aristichthys nobilis
  • Carassius gibelo
  • Cyprinus carpio

Figure 1, 2 and 3 provides an overview of the identification features for fish that are used in the key.


Figure 1 & 2: The main outline features of a fish



 Figure 3: Front view of a fish with the different fins