Quantifying invasion pathways: fish introductions from the aquarium trade

Introduced species can cause economic and environmental harm. Researchers have developed risk assessment models for exotic species based on biological characteristics. However, few have quantified propagule pressure despite its relevance for establishment. Both are needed to identify invasion risk. We focused on fishes introduced via the aquarium trade, because this pathway transports thousands of species throughout the world. We developed an approach to estimate propagule pressure by (i) identifying and quantifying aquarium fishes sold, (ii) determining fish owner behavior and disposal practices, and (iii)quantifying uncertainty. We used the St. Lawrence Seaway as our model system. Only one nonestablished species (Tanichthys albonubes, 117 per year) had the propagule pressure and environmental tolerances to likely invade this region. However, overall, more than 10 000 fishes were released annually from Montreal (Quebec, Canada) alone. The implication of the observed propagule pressures is that the aquarium trade should be a very important pathway in other warmer habitats and should be explicitly assessed. Knowledge of the numbers introduced of each species will be useful for population models to estimate the probability of establishment.