The diet and reproduction of fish communities in three biotopes (river, stream, and lake) of the Mesay floodplain-river complex (Puerto Abeja, Serranía de Chiribiquete National Natural Park, Caquetá, Colombia) were sampled during the “high water” level or flooding period. A total of 79 species of fishes from 15 families and four orders were collected between July and September 2000. The most important items in their diet were fruits and seeds. Approximately 46 % of captured fish were near maturity, and 35 % were mature. The feeding and reproductive behavior of these fish were consistent with other studies on migratory Amazonian species during the high water period, when the floodplain plays an important role in the availability of food and refuge. During this period the fish make use of the vast food availability to accumulate fat reserves that later produce the energy needed for gonadal maturation and breeding migrations.