Irish fish species include those found in the sea, our coastal species, and those that live in our freshwater systems, i.e. mountain streams, lowland rivers and lakes. Some of our native freshwater species are found in both fresh and salt water, as they are 'anadromous', which means they migrate from the sea to rivers and streams to breed, for example, the lamprey and salmon. Other fish that breed at sea but enter Irish freshwaters to feed and grow are known as 'catadromous' fish, and include the Flounder and the Freshwater Eel.
All of the freshwater species found here today must have arrived in Ireland in the course of the last 10,000 years, since the last glaciation, because before this the country's waters were frozen and its valleys and lowlands were covered by ice. Therefore all of our current fish species either swam here by sea or were introduced by man.
Three of our native species are now confined to freshwater: the Arctic Char, Pollan and Killarney Shad. These species are probably descendents of populations that originally travelled here by sea and lived an anadromous life for a long period before losing the migratory habit. It is believed that the Arctic Char was the first freshwater fish to colonise Ireland after the last Ice Age. It requires cold, clean water, and has the most northerly geographic distribution of any freshwater fish, being common along the frozen coastline of the Arctic Ocean. Irish populations of the Arctic char represent the extreme limit of its southerly distribution. The Char is now confined to deep mountain lakes in the west, from Donegal to Kerry. Populations in the midlands and east of the country became extinct in the 19th century, due mainly to pollution and competition from introduced species.
Other native fish include the River Lamprey, Salmon, Trout, and Stickleback. The Lamprey feeds on the blood of other fish, by attaching its toothed sucker to a host fish. Despite the threats of industrial and rural pollution, Ireland still has some of the best salmon and trout rivers in western Europe.
Eels are amazing creatures that breed in the Sargasso Sea, about 4,000km across the Atlantic, and are therefore catadromous. They arrive in Ireland when they are about three years old and spend ten to twenty years in rivers and lakes. When they have accumulated enough reserves in their bodies, in the form of oil, they migrate to their breeding grounds, travelling thousands of kilometres without eating.
The remaining freshwater fish were introduced by man, including Carp, Tench, Minnow, Gudgeon, Rudd, Stone Loach, Dace, Roach, Pike, and Perch. Many of these introductions have led to serious reductions in numbers of the more valuable native fish.
Marine species found in Irish waters include jawless fish (the sea lamprey for instance), bony fishes and cartilaginous fishes - the sharks, skates and rays, which have a skeleton made of tough, flexible cartilage.
The Lesser Spotted Dogfish, Scyliorhinus canicula, a member of the shark family, is common and widespread around the Irish coast. It lays its eggs in long, leathery cases, called 'Mermaid's purses', attached to seaweed by fine tendrils. Mermaid's purses are often seen washed up on Irish beaches. The Thornback Ray, Raja clavata, is another common cartilaginous fish in Irish waters.
Other fish found in Irish waters include Pollack, Whiting, Codfish, Mackerel, Mullet, Flatfish, Gurnard, John Dory, Perch, Bass, Conger eel, Salmon, Trout, Herring, Shad, Garfish, and Sea-horse. One of the most intriguing fish found in Irish waters is the Basking Shark, Cetorhinus maximus. This giant shark can reach 15 metres in length and is the world's second largest fish, second only to the Whale Shark which lives in tropical waters. Despite its intimidating size, the Basking Shark is harmless, living on plankton, which it filters with its gills as it cruises through the water, its mouth agape.
Salmon Salmo salar (Photo: Mike Brown)
Kurz, I. And Costello, M. J. (1999) An outline of the biology, distribution and conservation of lampreys in Ireland. [2,483KB] King, J. J. & Linnane, S. M. (2004) The status and distribution of lamprey and shad in the Slaney and Munster Blackwater SACs. [1,095KB] King, J. J., (2006) The status and distribution of Lamprey in the River Barrow SAC. [665KB] O'Connor, W., (2006) A baseline survey of juvenile lamprey populations in the River Feale catchment. [1,007KB]