This video from Britain says about itself:
European bitterling (Rhodeus amarus) Underwater UK
9 March 2015
Scattered in England and Wales, with key populations established in north-west and eastern England. Likely to have been introduced for ornamental reasons, its introduced range in GB is linked to the presence of Unionid mussels required for reproduction. The species is endangered in parts of its native range (water pollution, weed clearing, and stocking of predatory fish).
Translated from the Dutch RAVON ichthyologists:
13 January 2016 – As of January 1, 2016, the new Red List of Fish came into force. RAVON carried out the analysis for species living in fresh water. Of the more than 40 species that breed within the Dutch borders there are 19 in the new Red List. Almost as many as the previous Red List in 1997. It is hopeful that the degree of threat for some species has decreased.
How are the freshwater fish?
For the Dutch Red List, a comparison is made between the population size in the baselines of 1950 and the current situation. The first Freshwater Fish Red List was drawn up in 1997 (and revised in 2004). Compared to this list, there are five new species to the new Red List, two species (smelt and bleak) because they have declined; two species (river lamprey and sea lamprey) because it has turned out that they reproduce in the Netherlands; and one species (Cottus rhenanus) which has recently been established as a separate species. Two species (bitterlings and Leucaspius delineatus) are no longer on the Red List because they have increased and probably also because they seem far more widespread as a result of better identification than previously suspected.
Over time, humans have contributed to the loss of native species and have introduced non-native species throughout Europe. A new analysis shows how European freshwater fish have changed profoundly since 1840. At the continental scale, the contemporary fauna holds net 11 more species today as exotic species introduction (26 species) exceeded native species loss (15 species). But the biggest change was made by European species introduced from one area in Europe to another (77 species), often with fatal results: here.