Fish species of the Finnish marine areas

There are just over 60 species of fish found in Finnish marine areas. The varied early history, as well as the brackish water of the Baltic Sea, have led to the emergence of fish species ranging from oceanic to freshwater.

These species include those adapted to both cold and somewhat warmer water. Compared to oceans and tropical inland waters, the number of fish species are small, which is explained by the fact that the Baltic Sea is also younger in its history, as well as more environmentally diverse.

Different species of fish have different requirements for their environment and the demands of the breeding area often form the limiting factor for the stock size. The key factors are the oxygen content, salinity, temperature and how protected the water is. In addition to the reproductive cycle, temperature also plays an important role in controlling the occurrence and migration of adult fish.

A butterfish rests among red algae and blue mussels.
The rock gunnel or butterfish is Finland’s least known fish species.

There are only about 20 true marine species

Of the marine species, the familiar and most important in Finnish commercial fisheries is the herring, i.e. Clupea harengus. Although they remain small in relation to their ocean relatives, good growth and survival rates of Baltic herring in their first year will result in excellent herring production, relative to the water volume in the Baltic Sea.

Baltic herring, sprat, European smelt, three-spined stickleback, and several goby species occur in abundant numbers, particularly in open water areas. Although the European eel and cod cannot reproduce in Finnish marine areas, their individuals arrive and grow in the Baltic Sea after their juvenile life stages are complete.

Salinity limits the occurrence of freshwater species

Freshwater species such as roach and perch are most abundant in low-saline and sheltered coastal waters. They utilise different archipelago zones, depending on the species and the season. Of the freshwater species, approximately half are either from the roach- or carp families and their share of biomass also seems to increase with eutrophication and warming.

Although the majority of freshwater fish species migrates to rivers, estuaries or inland lakes to reproduce, others can take also advantage of the most sheltered bays, flad-lakes and streams of the outer archipelago areas.

Migratory fish depend on both fresh- and saltwater areas

Trout, salmon, lampreys, dace, vimba bream, and ziege migrate up rivers to spawn in freshwater. Although they are completely dependent on freshwater for reproduction, they may migrate far to sea to feed.

Over time, whitefish and grayling have also evolved forms which spawn in the sea. Their stocks and those of other migratory fish have fallen sharply as a result of rivers being dammed, construction on water bodies, and increasing nutrient-loads. Indeed, most migratory fish are classified as endangered.

By contrast, the abundance of invasive fish species, such as the round goby and the Prussian carp has increased markedly in Finnish marine waters over the past decade.

A sea trout rests on a bed of bladder wrack.
Sea trout are classified as critically endangered.

On this website we tell more about Baltic herring, which is the most important fish species for Finnish commercial fishery, and about perch which is a national fish of Finland. Of all the other fish species found in Finland, you can find good information from Natural Resources Institute Finland´s website (in Finnish) and from portal (in English).