Fishes and Amazonian habitats
It is easy to consider the Amazonian fishes as one large group, and assume that they lead similar lifestyles and have similar requirements. In fact, the range of different habitats supporting fishes is nearly as diverse as the fishes themselves. The main bodies of water are grouped loosely into black, white and clear waters, which will be dealt with in more detail in later sections. However, waters mix and mingle, creating areas where the composition is neither one thing nor the other, and the seasonal floods bring both chemical and other environmental changes.

Some of the fishes are hardy, and can be found in more or less any body of water they have been able to reach. Others are more specific in their requirements, and are restricted to a particular area or habitat; many of these are hindered from achieving a wider distribution by 'chemical barriers' - changes in water chemistry that they are unable to swim through to reach other waters. The widespread fishes are usually familiar in the aquarium trade and public aquaria (except where they are excluded because they are particularly large or aggressive, and even then the most unlikely fishes have fans somewhere). Others are unlikely ever to become familiar to most people - a tank filled with dead leaves containing microscopic fish is unlikely to provide much entertainment. However, the most fascinating fishes with remarkable adaptations are often those found in obscure habitats, that cannot be appreciated by the casual observer.