Chub (Leuciscus cephalus): a new potentially invasive fish species in Ireland

The chub is a freshwater fish of the family Cyprinidae, which is widely distributed throughout Europe. Prior to 2001 there were no reports of chub being present in Ireland. In 2001 and again in 2004 it was reported that an angler had caught chub in a section of the River Inny. On neither occasion were live specimens retained for authentication. In 2005 a number of live, angler-caught chub from this river were formally identified. In order to determine the status of this non-native and potentially invasive fish species in this renowned Irish coarse, game and pike fishery, an electric fishing survey was conducted in 2006. Seventeen chub were captured during this operation. All were taken from one relatively short (c. 0.8 km), shallow (≤0.5 m) and moderately fast flowing section of river. The fish ranged in fork length from 15 to 41 cm and in age from III+ to X+ years old. Among the fish captured, there were two immature fish, six females and nine males. The stomach contents revealed a diet of insect, fish, plant material and detritus. A relatively fast growth rate was recorded. While relatively few chub were captured during the survey, those examined were healthy and most were in spawning condition. It is considered that the chub were introduced to the river by anglers in an effort to increase the diversity of coarse angling species available in Ireland. The potential impact of the chub on natural biodiversity and on the community composition of native and naturalised fish species in the river is discussed.