As the Middle Ages drew to a close, however, a rising share of Europeans were eating fish from systems other than their natural local waters. By 1500 around Paris, for instance, elite menus featured carp and headless codfish, while lesser folk made do with herring and haddock. Beside the Mediterranean, Valencia was receiving millions of Atlantic sardines and hake, while Romans could get herring from the North Sea, Norwegian cod, and tuna from Sicily. Both cultured carp and fishes from Europe’s economic frontiers changed Europeans’ relations with aquatic nature.

Carp aquaculture colonized nature, creating artificial habitats to rear an organism alien to western Europe. Late fifteenth- and early sixteenth-century financial records and instructional manuals from east-central Europe detail an original and distinctive European mode for farming fish. Those practices provide a benchmark to identify and trace their creation in twelfth- to thirteenth-century France – where the carp was a late invader – and subsequent spread eastwards of the innovation. Human-controlled aquaculture created thousands of local ecological revolutions across interior Europe, providing inland elites with a steady source of live fresh fish, serving as a vehicle of elite power over subjected nature and people, and replacing indigenous ecosystems with private anthropogenic habitats tailored for domesticated, soon also feral, invaders. For contemporary writers fish had become objects of human agency.

Worldwide, freshwater biodiversity is in decline and increasingly threatened. Fishes are the best-documented indicators of this decline. General threats to persistence include: (1) competition for water, (2) habitat alteration, (3) pollution, (4) invasions of alien species, (5) commercial exploitation and (6) global climate change. Regional faunas usually face multiple, simultaneous causes of decline. Threatened species belong to all major evolutionary lineages of fishes, although families with the most imperilled species are those with the most species (e.g. Cyprinidae, Cichlidae). Independent evaluation of California’s highly endemic (81%) fish fauna for comparison with IUCN results validates the alarm generated by IUCN evaluations. However, IUCN overall evaluation is conservative, because it does not include many intraspecific taxa for which extinction trends are roughly double those at the species level. Dramatic global loss of freshwater fish species is imminent without immediate and bold actions by multiple countries.