Species list South American freshwater:
9 regions:
1 Rio Cauca
2 Orinoco basin
3 Collective Guianan rivers
4 Amazon basin
5 São Francisco river basin
6 La Plata basin
7 Colorado/Negro basin
8 Andean waters and the West Coast
9 East Coast
Fish in the Andean water and West Coast are a bit iffy, some simply occur higher up than most Amazon dwellers, such as the Julii corydoras and Black ghost knifefish:

Others truly occur on the West Coast:
Species list Rio Cauca:
Characins:
Spotted hatchetfish
Gar characin
Emperor tetra
Catfish:
Tete sea catfish**
Duckbill catfish
Brown hoplo
Palito
Royal twig catfish*
Livebearers and allies:
Guppy
Perchlikes:
Blue acara
Redhump eartheater
Species list Orinoco basin:
Freshwater stingrays:
Smooth-back river stingray
Knifefishes:
Black ghost knifefish
Livebearers and allies:
Endlers guppy
Guppy
Four-eyed fish
Puffers and filefishes:
Amazon freshwater puffer
Lungfishes:
South American lungfish
Characins:
Red tail hemiodus
Kissing prochilodus
Banded Leporinus
Goldstripe headstander
Marbled headstander
Striped headstander
Black-winged hatchetfish
Marbled hatchetfish
River hatchetfish
Spotfin hatchetfish
Golden pencilfish
Splash tetra
Black band myleus
Colossoma macropomum
Red hook silver dollar
Spotted silver dollar
Bucktooth tetra
Cardinal tetra
Diamond tetra*
Firehead tetra
Gold tetra
Green neon tetra
Ornate tetra
Red phantom tetra
X-ray tetra
Catfishes:
Giant raphael catfish
Southern striped raphael
Spotted talking catfish
Duckbill catfish
Pictus catfish
Redtail catfish
Tiger sorubim
Two-colored banjo catfish
Armoured catfish
Bandit corydoras
Bronze corydoras
Brown hoplo
Masked corydoras
Amazon whiptail catfish
Galaxy pleco
Lyre-tail pleco
Orinoco sailfin catfish
Royal panaque
Royal twig catfish*
Sabaj's leopard pleco
Spotted sailfin suckermouth catfish
Whiptail catfish (Farlowella acus)
Perchlikes:
Amazon leaffish
Altum angelfish
Banded cichlid
Blue acara
Keyhole cichlid
Parrot cichlid
Ram cichlid
Redhump eartheater
Speckled peacock bass
Tiger oscar
Species list Collective Guianan rivers:
Freshwater stingrays:
Smooth-back river stingray
Bony-tongued fishes:
Silver arowana
Knifefishes:
Black ghost knifefish
Electric eel
Livebearers and allies:
Guppy
Four-eyed fish
Puffers and filefishes:
Amazon freshwater puffer
Lungfishes:
South American lungfish
Characins:
Banded Leporinus
Goldstripe headstander
Striped headstander
Marbled hatchetfish
River hatchetfish
Golden pencilfish
Splash tetra
Black band myleus
Orange spotted pacu
Red hook silver dollar
Red-bellied piranha
Metynnis altidorsalis
Spotted silver dollar
Bucktooth tetra
Glowlight tetra
Gold tetra
X-ray tetra
Catfish:
Giant raphael catfish
Southern striped raphael
Ripsaw catfish
Duckbill catfish
Redtail catfish
Tiger sorubim
Two-colored banjo catfish
Armoured catfish and Corydoras:
Armoured catfish
Bronze corydoras
Brown hoplo
Three-lined cory
Amazon whiptail catfish
Leopard cactus pleco
Lyre-tail pleco
Sabaj's leopard pleco
Spotted sailfin suckermouth catfish
Common pleco
Temminck's Bristlenosed catfish
Perchlikes:
Butterfly Peacock Bass
Demon eartheater
Freshwater angelfish
Goldeneye cichlid
Keyhole cichlid
Krobia
Leopold's angelfish
Manacupuru angelfish
Peacock bass
Speckled peacock bass
Tiger oscar
Species list Amazon river basin:
Freshwater stingrays:
Black-tailed stingray
Pearled river stingray
Smooth-back river stingray
White-blotched river stingray
Bony-tongued fishes:
Silver arowana
Black arowana
Arapaima
Catfish:
Giant raphael catfish
Southern striped raphael
Ripsaw catfish
Spotted talking catfish
Duckbill catfish
Pictus catfish
Redtail catfish
Tiger sorubim
Two-colored banjo catfish
Corydoras:
Adolfs catfish
Armoured catfish
Bandit corydoras
Bronze corydoras
Dwarf corydoras
Emerald catfish
Flagtail catfish
Brown hoplo
Gold laser cory
Horseman corydoras
Julii corydoras
Panda corydoras
Porthole catfish
Saddle Cory
Schwartz's catfish
Skunk corydoras
Smudge spot cory
Spotted Corydoras
Spotted corydoras
Sterba's corydoras
Three-lined cory
Armoured catfishes:
Amazon sailfin catfish
Amazon whiptail catfish
Blue-eyed cochliodon
Bristlenose plecostomus
Candy striped plecostomus
Dwarf oto
Flash pleco
Galaxy pleco
Gold nugget pleco
Gold spotted pleco
Golden-Nugget catfish
Green phantom pleco
King tiger pleco (Hypancistrus spec. L 066)
King tiger pleco (Hypancistrus spec. L 333)
Leopard cactus pleco
Leopard frog pleco
Lyre-tail pleco
Polka-dot lyretail pleco
Sabaj's leopard pleco
Snowball pleco (Hypancistrus spec. L 102)
Spoon face whiptail
Spotted sailfin suckermouth catfish
Goldie pleco
Tapajos royal pleco
Xingu tiger pleco
Zebra pleco
Knifefishes:
Black ghost knifefish
Livebearers and allies:
Four-eyed fish
Puffers and filefishes:
Amazon freshwater puffer
Lungfishes:
South American lungfish
Characins:
Red tail hemiodus
Kissing prochilodus
Silver prochilodus
Banded Leporinus
Goldstripe headstander
Many-banded headstander
Marbled headstander
Striped headstander
Black-winged hatchetfish
Giant hatchetfish
Marbled hatchetfish
River hatchetfish
Spotfin hatchetfish
Golden pencilfish
Peruvian red pencilfish
Splash tetra
Black band myleus
Orange spotted pacu
Colossoma macropomum
Pirapitinga
Red hook silver dollar
Red-bellied piranha
Metynnis argenteus
Spotted metynnis
Spotted silver dollar
Amapá tetra
Black neon tetra
Black phantom tetra
Blackline penguinfish
Bleeding heart tetra
Blueberry tetra
Bork's tetra
Bucktooth tetra
Cardinal tetra
Dawn tetra
Ember tetra
False Kitty tetra
False rummynose tetra
Firehead tetra
Glass bloodfin
Gold tetra
Green neon tetra
Jewel tetra
Lemon tetra
Triangle glass tetra
Neon tetra
Ornate tetra
Phoenix tetra
Redeye Tetra
Rosy tetra
Royal tetra
Rummy-nose tetra
X-ray tetra
Dorado
Piraputanga
Pinktail chalceus
Tucan fish
Perchlikes:
Amazon leaffish
Agassizs dwarf cichlid
Altum angelfish
Banded cichlid
Blue discus
Bolivian Butterfly cichlid
Butterfly Peacock Bass
Cockatoo cichlid
Common severum
Demon eartheater
Discus fish
Emerald cichlid
Mesonauta festivus
Freshwater angelfish
High-head eartheater
Kelber's peacock bass
Leopold's angelfish
Manacupuru angelfish
Parrot cichlid
Peacock bass
Red discus
Speckled peacock bass
Sven's eartheater
Tapajos redhead eartheater
Tiger oscar
Uaru
Species list São Francisco river basin:
Characins:
Spotted silver dollar
Banded astyanax
Blackline tetra
Buenos Aires tetra
Redeye Tetra
Silvertip tetra
Banded characidium
Catfish:
Ripsaw catfish
Bronze corydoras
Brown hoplo
Hypostomus punctatus
Livebearers and allies:
Four-eyed fish
Lungfishes:
South American lungfish
Species list La Plata basin:
Freshwater rays:
Ocellate river stingray
Catfish:
Southern striped raphael
Barred sorubim
Duckbill catfish
Armoured catfish
Bronze corydoras
Brown hoplo
Peppered corydoras
Amazon whiptail catfish
Chocolate pleco
Jumbie teta bristle-nosed plec
Knifefishes:
Black ghost knifefish
Lungfishes:
South American lungfish
Characins:
Marbled headstander
Spotfin hatchetfish
Red-bellied piranha
Spotted metynnis
Spotted silver dollar
Black neon tetra
Black phantom tetra
Black tetra
Dawn tetra
Jewel tetra
Redeye Tetra
Dorado
Piraputanga
Banded characidium
Perchlikes:
Flag cichlid
Pearl cichlid
Species list Colorado-Negro basin:
Yet another species list I included in the beginning, not knowing it would have very few species...
Freshwater rays:
Ocellate river stingray
Catfish:
Peppered corydoras
Species list Andean waters and the West Coast:
Characins:
Spotted silver dollar
Catfish:
Tete sea catfish**
Armoured catfish
Brown hoplo
Horseman corydoras
Julii corydoras
Masked corydoras
Panda corydoras
Spotted corydoras
Whiptail catfish (Farlowella acus)
Knifefishes:
Black ghost knifefish
Lungfishes:
South American lungfish
Cichlids:
Demon eartheater
Mesonauta festivus
Green terror
Guayas cichlid
Tiger oscar
Species list East coast:
Characins:
Spotted silver dollar
Flame tetra
Banded characidium
Catfish
Banded corydoras
Bronze corydoras
Coast cory
Brown hoplo
Peppered corydoras
Blue-chin catfish
Golden otocinclus
Hypostomus punctatus
* = These species don't occur perfectly within the river system they're classified under, but they do occur nearby.
** = The Tete sea catfish can be held in Fresh water as a juvenile, but has to be acclimated to Marine water as it matures