EXTENSIVE HYBRIDISATION BETWEEN ROACH, RUTILUS RUTILUS L., AND COMMON BREAM, ABRAMIS BRAMA L., IN IRISH LAKES AND RIVERS

摘要

Widespread hybridisation between roach (Rutilus rutilus L.) and common bream (Abramis brama L.) was recorded throughout Ireland in the 1970s and 1980s following the establishment of invasive roach populations. To identify the post-invasion levels of hybridisation, a fish stock monitoring program was implemented in lake and river sites, predominantly within the extended River Shannon catchment. Roach × bream hybrids were the second or third most prolific fish recorded during these surveys, accounting for approximately 20%—30% of fish caught. The abundance of roach × bream hybrids is unique to Ireland and represents a potential threat to bream populations in invaded catchments.