To understand the fish that live in black water habitats it’s imperative that there is a proper understanding of what black water is and what makes it unique. The term “Black Water” is a term that refers to very soft/acidic water which is stained brown from the accumulation of tannic, humic, and fulvic acids. These acids form and accumulate when various organic matter decomposes in aquatic environments particularly dead plant matter. Due to the coloration and the chemistry of the water many black water habitats house very interesting and unique populations of fish which have evolved to survive in such environments. Another thing noteworthy about black water environments is the lack of aquatic plant life which oftentimes struggle to survive in such conditions. These habitats can be found throughout the world but the most notable are those within South America such as the Rio Negro and the Orinoco.
Examples of popular aquarium fish the naturally live in black water environments are neon/cardinal tetras, rummy nose tetras, discus, angelfish, loaches, uaru and various species of catfish and dwarf cichlids like apistos. Unfortunately, a lot of these fish that come from black water habitats have earned a reputation for being rather delicate and sensitive in the hobby. This is in part due to their preference for water that is soft/ acidic but more importantly is their adaptation to water that have generally low bacteria counts due to the black water conditions. With soft/acidic water that is low in minerals many types of bacteria struggle to survive and populate in large numbers. As a result, to this many species of black water fish have also adapted with immune systems that are not as genetically strong or robust.
With this knowledge aquarist should keep in mind that fish from black water habitats require “clean” water that has low levels of pathogens. This can be achieved with proper husbandry via maintenance and water changes, aggressive filtration, U.V Sterilization and utilizing water that is soft and acidic with low levels of minerals in particular salts. The further addition of Indian almond leaves which have anti-microbial properties will further help in reducing pathogens while also promoting and recreating natural black water conditions which these fish thrive in.