The lateral migration an undescribed species of Arapaima has been studied in a paper published in the most recent issue of the journal Ecology of Freshwater Fish.
The study by Leandro Castello of the Mamirau Sustainable Development Institute, counted pirarucu within transects set out in the Mamirau Sustainable Development Reserve at the confluence of the Solimes and Japur Rivers over an entire (annual) flood cycle.
There are two forms of migration observed in floodplain fishes: longitudinal (along the main river channel) and lateral (between the main river channel and the floodplain), with lateral migration being the more poorly-studied of the two.
Water level fluctuationsThe author found that he lateral migration of the pirarucu accompanied water level fluctuations closely...As water levels rose, the pirarucu migrated to increasingly higher habitats in flooded forests, and as water levels declined, the pirarucu migrated first back to lower habitats of flooded forests, then to communicating channels, and eventually to the lakes.
He also found that pirarucu preferred shallow, slow flowing habitats.
There are two advantages for the pirarucu to inhabit the flooded forests and, in particular, to migrate into them immediately after they are flooded: feeding and parental care.
"...the species of pirarucu studied is actually undescribed..."
The pirarucu aged about 1 year and older feed primarily on fish...Four fish families comprise about half of all ingested food in weight; these are species of the families Callichthyidae, Loricariidae, Pimelodidae, and Heptapteridae, in order of decreasing importance...Most such fishes are detritivorous or omnivorous, and several species of Callichthyidae and Loricariidae are adapted to hypoxic conditions, tend to be nonmigratory, and inhabit these floodplains throughout their life cycles...
With exception of the Callichthyidae, the three other prey groups are reported to inhabit the flooded forests during high water levels...Thus, they are likely to constitute constant food sources for the pirarucu. This is especially so early in the flood when these prey species find generally higher oxygen levels...
The flooded forests offer many species of insects, fish larvae, and other small organisms...for the offsprings of the pirarucu to eat...In addition, floating meadows constitute ~an important nursery habitat for a great number, perhaps the great majority, of fishes in the vrzea ...
Conceptual modelThe study furthers our understanding of lateral migration in floodplain fishes and allows a conceptual model of such migration to be constructed.
The author also noted at the end of the study that the species of pirarucu studied is actually undescribed.
For more information, see the paper: Castello, L (2008) Lateral migration of Arapaima gigas in floodplains of the Amazon. Ecology of Freshwater Fish 17, pp. 38"46.