Marbled Hatchetfish Identification Guide

Key identification features

• Deep, laterally compressed body with a pronounced downward-bulging keel that gives it a hatchet-blade silhouette
• Silvery base color overlaid with an irregular brown to olive marbled or netted pattern along the upper body
• Small, upturned mouth positioned for snapping insects from the water's surface
• Oversized pectoral fins anchored to strong chest muscles, used to whir rapidly and glide short distances above the water
• Compact size, typically 3.5-4.5 cm, with a short, slightly forked tail

Common look-alikes

• Silver hatchetfish: shares the keeled body shape but has plain, uniform silver flanks without the marbled brown pattern
• Common hatchetfish: similarly deep-bodied, but shows a bolder solid dark stripe along the flank instead of a mottled marbling
• Black-winged hatchetfish: distinguished by dark, almost black pigment along the dorsal edge and pectoral fin bases, absent in the marbled form

Where you'll see one

Found in slow, still, and densely vegetated blackwater streams, forest pools, and flooded areas across the Amazon basin, this species stays near the surface in shaded, leaf-littered water where it can launch into short glides to escape predators.