Invasive Alien Species in Northern Ireland

Rutilus rutilus, Roach

Rutilus rutilus Linnaeus, 1758
Since, unlike Great Britain, Ireland had no freshwater connection to the rest of Europe at the end of the last ice age, all purely freshwater fish (that is, fish that cannot live in sea water) including those of the Cyprinid family (roach, rudd, common bream, common carp, common gudgeon, tench, dace and minnow), and others such as perch and pike, have been artificially introduced to Ireland. Of these introduced alien species roach is one of the most invasive and prolific freshwater fish species and has been associated with declines in native fish and other species. Roach is an important ‘coarse’ angling species and small roach (alive or dead) are often used as bait in angling for pike and ferox trout.
The roach is a deep-bellied freshwater fish of the carp family. Typically the fish can grow to 30cm in length with fish of over 40cm and 1.5kg having been recorded. Roach can live for up to 15 years. The back is greenish- or bluish-brown with large silvery scales on the side. The fins, especially the pelvic and anal ones, are orange or red in colour, as is the iris of the eye in older fish. Roach looks superficially similar to the rudd. The two can normally be told apart by the relative positions of the dorsal (back) and pelvic fins (rear paired fins). In the roach the front of the dorsal fin is directly above the base of the pelvic fins, whereas in the rudd the front of the dorsal fin is behind the base of the pelvic fins. However, the roach interbreeds readily with both rudd and bream producing fertile hybrids, and in some waters hybrids are more numerous than the parental species. Hybrids can be difficult to identify without detailed morphological or genetic analysis. There is also confusion due to the fact that rudd are referred to as roach in some parts of Ireland.
Country of origin
The roach is native to much of Great Britain, northern Europe and Asia.
Current distribution
The roach is now found throughout most of northern Europe and Asia from the Baltic Sea southwards to Iberia and Turkey.
Location in Ireland
Roach was first introduced into Ireland to the Cork Blackwater in 1889 having been brought over as live bait from England by a pike angler. Within a few decades it had spread throughout that water system. Roach from the Blackwater were introduced into a lake in Baronscourt Estate, County Tyrone in 1905 as food for pike. From there they escaped during a flood into the Foyle system. Roach were deliberately introduced into the Erne system in the 1930s and by the mid-sixties they were widespread and common in that system. From the Erne they were introduced into the Neagh system, with the first recorded occurrence in Lough Neagh being in 1973. Roach can live in nutrient-enriched waters with low oxygen content and is now widespread and common in many still and running waters in Northern Ireland and its range continues to expand. For example, it has been introduced into Lough Melvin within the past few years and is now present in substantial numbers. In the Republic of Ireland it is present throughout the Shannon, Corrib, Boyne, Dee, Liffey and Cork Blackwater systems as well as many small lakes.
Life cycle
The roach spawns in April to June in shallow waters, often where there are dense submerged weeds. The female produces many thousands (up to 100,000 per kg) of minute eggs (c.1mm). The eggs are adhesive and stick to plants and stones. The eggs hatch after a few days. Roach feed on a wide variety of plant and animal material including plankton, algae, water plants, crustaceans, snails and insect larvae. The high rate of reproduction and generalised feeding behaviour mean that roach can increase rapidly in numbers. However, the roach typically shows dramatic variations in numbers from year to year. When large numbers are present, growth is often stunted.
Wildlife and habitat impacts
Roach can have a significant impact on water quality through accentuating the effects of nutrient enrichment. The abundance of roach and its feeding habits mean that it competes both directly and indirectly with other freshwater fish for food and quickly becomes the dominant fish species. Roach has been shown to reduce Atlantic salmon and brown trout numbers. The introduction of roach has been linked to the extinction of the Arctic charr (Salvelinus alpinus) in Lough Corrib and to the severe decline in pollan numbers in Lower Lough Erne. It has led to reduction in numbers of rudd, an alien fish species introduced sometime prior to roach. In Lough Neagh competition for food with roach has been found to reduce the numbers of overwintering tufted duck (Aythya fuligula). However, the numbers of great crested grebes (Podiceps cristatus) increased, presumably as a result of the increased availability of small fish as food. Movement of roach could potentially result in the introduction of diseases and parasites.
Human impacts
Wild Atlantic salmon and brown trout populations are important economic resources for tourism and recreation. However, angling for roach is popular and is similarly an important economic resource.
Key vectors
Most spread is due to deliberate introductions to establish angling stocks or through use as live bait in pike or ferox fishing. Although illegal, this is still undertaken, as earlier this year two pike anglers from England were stopped with containers of live roach and carp as they boarded the ferry at Holyhead.
What you can do as an individual
Do not move roach to waters where they do not occur and do not use them as live bait (illegal anyway).
Advice to specific groups relevant to this species
Roach should not be introduced into waters where they do not already occur.
Management measures
Once introduced, it is effectively impossible to eliminate roach from larger waters. Numbers can be reduced through reduction in the amount of nutrients entering water systems, a desirable measure for many other reasons.
Management groups
Environment and Heritage Service Northern Ireland
Department of Culture Arts and Leisure Northern Ireland
Fisheries Conservancy Board Northern Ireland
Loughs Agency
Central and Regional Fisheries Boards Republic of Ireland
Further information
Maitland, P.S. (2004). Keys to the freshwater fish of Britain and Ireland, with notes on their distribution and ecology. Freshwater Biological Association Scientific Publication No. 62. (available from the FBA Publications Department -
Winfield, I.J., Winfield, D.K. and Tobin, C.M. (1992). Interactions between the roach Rutilus rutilus and waterfowl populations of Lough Neagh Northern Ireland. Environmental Biology of Fishes 33: 207-214.
Text written by:
Prof. Andy Ferguson