On Species of Fresh Water Fish, found in Iceland.

 

There are five species of freshwater fish in Iceland. Three of these belong to the salmon family (Salmonidae); the Atlantic salmon (Salmo salar L.), the Arctic char (Salvelinus alpinus L.) and the brown trout (Salmo trutta L.).

The other species are the three-spined stickleback (Gasterosteus aculeatus L.) and the eel (Anguilla anguilla). All these species require to or are able to live in the sea for part of their life cycle, which explains how they originally arrived on this Atlantic island.

The rainbow trout (Oncorhynchus mykiss) has been introduced to Iceland by fish farmers, and the occasional humpback salmon (Oncorhynchus gorbuscha) is also found here, presumably originating from Russia or the eastern seaboard of Canada. However, these two species are not known to breed in Iceland, though they are sometimes caught here.

 

Life cycle
   

Fish species which migrate between marine and fresh water often have complicated life cycles.

The salmon spends the first years of its life in fresh water as fry before migrating to the sea, where it spends one to two years before returning to the home river to spawn.

The Arctic char and brown trout have two different types of life cycle. Both species can either spend their entire life in fresh water (landlocked Arctic char or landlocked brown trout), or spend their first years in fresh water as fry, before later migrating to the sea every summer and returning every winter to the home river (sea Arctic char and sea trout).

Both landlocked and sea Arctic char are common throughout Iceland, whereas the sea trout is mainly to be found in the south and west of the country. Although the journey to the sea can be long and hazardous, there are also advantages to spending time in marine water. The sea has a more varied ecosystem than fresh water and therefore a greater abundance of organisms for larger fish to feed on, resulting in a better rate of growth in marine fish than in freshwater varieties.

 

Distribution
    
The distribution of Icelandic salmonids is dependent on their choice of habitat.

Although the species are similar and compete with each other for food, they all have different habitat requirements.

The char is a tough Arctic species which can live in cold, inhospitable waters. It is therefore well adapted to spawning and spending its first years on fine gravel river or lake beds and in calmer water than the brown trout or salmon.

The salmon is generally dominant in rivers rich in nutrients, choosing to live in stronger currents and on stonier river beds.

The brown trout comes somewhere between the char and the salmon in its habitat requirements relating to temperature, strength of current, type of river bed and level of nutrients.