Gold!

It's a fairly obvious reminder but people are being urged not to throw their redundant goldfish into British lakes, rivers and canals (https://www.theguardian.com/environment/2022/may/25/shiny-but-deadly-dont-throw-goldfish-in-rivers-pet-owners-told). Although goldfish are renowned only for their short attention spans, they are actually extremely voracious and combatative fish. Introducing this alien to UK freshwater habitats, can decimate natural populations. Goldfish, could join Parrot's feather pondweed and terrapins, as inadvertent additions by jaded aquarium keepers, that went on to cause massive environmental damage.