Non-native fish in the fresh waters of Portugal, Azores and Madeira Islands: a growing threat to aquatic biodiversity

Abstract  Portugal, the Azores, and Madeira had a combined total of twenty six non-native fish species introductions, with the mainland having the highest number (twenty three), followed by the Azores with ten and Madeira with two records. Fifteen of these species established in Portugal, six in the Azores and one in Madeira. The oldest known introduction (1792) was goldfish, Carassius auratus (L.), while the newest (2005) was tinfoil barb, Barbonymus schwanenfeldii (Bleeker). Ten species had been introduced in Portugal by the beginning of 20th century, but the rate of introduction continues to increase, with four species introduced since 2000. In mainland Portugal, the Douro, the Tejo and the Guadiana drainages had the highest number of introduction records, while the Lima and the Mira drainages had the fewest. Management measures are offered to reduce current rate of fish introductions in Portuguese watersheds.