probably a brain-dead question..

magicbastarder

but how do freshwater fish get into rivers?
specifically after the last ice age, and especially on the west coast which would have not been part of a land bridge. when the ice retreated, how did salt-intolerant fish or crustaceans make their way back into the river system?

Birdnuts

magicbastarder wrote: »

but how do freshwater fish get into rivers?
specifically after the last ice age, and especially on the west coast which would have not been part of a land bridge. when the ice retreated, how did salt-intolerant fish or crustaceans make their way back into the river system?

Ireland actually has very few native freshwater fish - of the ones we do have, most are salmonids that are very tolerant of icy water eg. Arctic charr, that would have survived in parts of the country during the last ice-age. Other salmonids like Sea-Trout and Salmon would have got here by sea since its part of their life-cycle. As regards Brown and other Trout species, I suspect they evolved from over time from their sea-going cousins.

Kess73

Not a stupid question.

A lot of the current Irish freshwater fish species were introduced into Irish waters by various groups who came to Ireland hundreds and hundreds of years ago.

The pike for example has been traced back to the 14th century when it was introduced by monks who brought live pike from the UK. But the same species in the UK managed to survive the ice age as fossilised pike dating back some 500,000 years have been found in Britain. They are meant to have originally gotten to the UK through some of the UK rivers being linked with the Rhine river by the North sea.


I would imagine that some Irish fresh water species came to Ireland via the north sea link as well, but seeing as Ireland has less species of freshwater fish than most other European countries, it strongly suggests that most were introduced here by travellers over the centuries bar the species that live in sea water and breed in freshwater like salmon, eel etc.

Half-cocked

Birdnuts wrote: »

As regards Brown and other Trout species, I suspect they evolved from over time from their sea-going cousins.

Sea Trout and Brown trout are the same species. Advances in DNA testing have proven that. Some brownies head out to sea, others stay in the rivers. Being able to tolerate saltwater probably explains how they got here.

cuddlycavies

All of the above plus the spread of spawn from waterway to waterway on the feet of birds.

slowburner

The freshwater species native to Ireland is actually a very short list: Salmon, Trout, Char, Shad*, Lamprey, Eel*. They are all migratory and saltwater tolerant. They colonised the waterways after the last ice age, although it is believed that there was a race of trout here before the last ice age (DNA research indicates that remnants of this race persist in the Ferox trout population and the large sea trout of the Waterville catchment).
All other fish (Pike, Bream, Rudd, Roach, Perch, Minnow, Stickleback, Dace etc.) were introduced by man. As to how introduced fish travel from waterways that are not linked to other waterways - usually man again - indeed there are laws designed to prevent this.
Most of the introduced fish tend to lay eggs which are sticky - theoretically, they could stick to something which travels between watercourses, the legs of wading birds or nets for example, and be transported that way.







*Anadromous - feeds at sea, breeds in freshwater
*Catadromous - feeds in freshwater, breeds at sea
It is very possible that this list omits some native fish