Leporinus santosi
Hypomasticus santosi is a small, recently described headstander (family Anostomidae) confined to clearwater tributaries of a single Amazonian river drainage in Brazil.
Topping out around six inches, it's the kind of fish that exists almost entirely in the scientific literature — not a sport fish, but a window into how much Neotropical freshwater diversity remains poorly understood.
Scientific Name: Leporinus santosi
- Three prominent dark blotches run along the midlateral line, with smaller pigment blotches between the head and the first blotch forming a broken 'X' pattern.
- Terminal mouth armed with four chisel-like incisiform teeth on both the upper and lower jaw — a hallmark of the Anostomidae family.
- 16 scale rows around the caudal peduncle (versus 12 in the closely related Hypomasticus gomesi) — the key count for separating the two species.
- Complete lateral line with 33–34 scales; maximum size around 155 mm (roughly 6 inches) standard length.
What to know
Habitat Distribution
- Restricted entirely to the lower Tocantins River drainage in Brazil — one of the narrowest geographic ranges documented for any Anostomidae species.
- A clearwater stream specialist, occupying tropical freshwater tributaries where it lives in the water column close to the bottom (benthopelagic habit).
- Much of its native habitat has been altered by the Tucuruí Dam, one of the largest hydroelectric projects in the Amazon basin.
Specific Spots
- No within-waterbody habitat data exists for this species; it occupies clearwater stream environments within a remote, highly restricted range and is not targeted by anglers.
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