The stone loach is native throughout most of Europe and Asia, but it is not native to Ireland. Stone loach are thought to have been introduced to Ireland and redistributed to angling waters as live bait, which possibly explains their somewhat erratic distribution around the country. Although it is an introduced species, stone loach are considered benign as they have no significant impact on native species or ecosystems.
The stone loach is perhaps the most cryptic species in Ireland's freshwater fish fauna, but it is nonetheless a fascinating little fish. Stone loach are well camouflaged to blend into their preferred habitat on the bottom of streams, small rivers and shallows near lakeshores, with a brown body mottled with dark patches. They have two pairs of barbels around their mouths, which helps them to grub for invertebrate prey buried in sand and gravel. Although they are not a shoaling species and are usually solitary, nocturnal creatures, they are frequently found in small groups when feeding. Spawning takes place in the spring and summer among gravel and aquatic vegetation.
Although they prefer clean water, stone loach are hardy fish and can tolerate moderate levels of pollution and nutrient enrichment in rivers. Uniquely amongst Irish fish, they are able to gulp air and absorb oxygen in their hindgut, which helps them to survive droughts and low oxygen conditions in shallow waters that other fish species could not survive.