The answer isn't simple, because seasons in the rainforest do not correspond to specific seasons as we temperate zone dwellers know them.  The best season is the "dry" season.  Rivers in Amazonia all experience an extended cyclical period of low rainfall sometime during the year, when the rivers reach their minimum flow.  This relatively dry, low seasonal period is the only productive time to fish for peacock bass.  During the long "rainy" season, Amazonian rivers typically overflow their banks and inundate huge areas of lowlying jungle   This flooded jungle (known as 'igapo' and 'varzea' in Brazil) offers superior forage for various species of baitfish.  Their predators, especially peacock bass, follow them into the flooded vegetation.  During the almost eight months of high water, rivers can occupy a surface area often hundreds of times larger than during the dry season;  peacock bass become all but impossible to catch.
    When the rains stop, the rivers begin to withdraw within their banks.  The baitfish head back into the main river bed and connecting lagoons to avoid being stranded in the rapidly drying 'varzea'.  The peacocks follow as well and begin to gorge on the now concentrated food supply.  This pre-spawn period during the early part of the 'dry' season is when their accessibility and their aggressive feeding make them the most exciting freshwater fish in the world.  The post-spawn period features hungry fish, seeking to regain the weight they lost during spawning.  These periods vary in their timing from river to river.

The dry season begins in the southern part of the Amazon basin in July and August.  Southern rivers such as the Rio Marmelos or Rio Jari begin to provide great fishing in August.  As the dry season progresses on these rivers, the well-fed peacocks begin to set-up to spawn (after about six weeks).  As the fishing diminishes in the south, rivers further to the north begin to get dry.  The dry season moves slowly north during October and November placing other rivers such as the Matupiri and the Caures among the optimal destinations for peacock bass in Brazil.  By December, the dry season moves north of the main body of the Amazon itself and rivers such as the Juferi, the Macucau, the Tapera and the Araca provide the best Brazilian peacock bass fishing on into March.
    Venezuela's dry season corresponds with Brazil's 'northern' dry season, starting in December and running through March.  The peak here is late December through January.  Peru's peak season is August through October.  Bolivia's peak season is December 15 through the end of January.   Although the answer is complex, it simply means that great peacock bass fishing is available somewhere in Amazonia from August through March.  To keep it simple, Acute Angling will make certain that you're a properly advised angler who takes advantage of the seasons by fishing the right rivers at the right time.