Diamond Killifish Identification Guide

Key identification features

• Very deep, strongly compressed body giving a rhomboid or diamond outline when viewed from the side
• Small size, usually under 5 cm, with a short, blunt snout and small upturned mouth
• Base color is silvery-tan to olive, often with faint vertical barring along the flanks
• Breeding males develop a yellow to orange wash on the fins and lower body
• Dorsal fin set well back on the body, relatively tall relative to overall body depth
• Rounded caudal fin without filamentous extensions, distinguishing it from lyretail-finned killifishes

Common look-alikes

• California Killifish: has a more elongated, cylindrical body rather than a deep diamond shape
• Blackstripe topminnow: slender and torpedo-shaped with a bold dark lateral stripe, unlike the Diamond Killifish's deep, barred body
• Golden Topminnow: lacks the compressed diamond profile and instead shows a slimmer, more typical topminnow build

Where you'll see one

Found in salt marshes, tidal creeks, and brackish lagoons along the Gulf Coast and southern Atlantic coast of the United States, often among cordgrass and other emergent marsh vegetation. It tolerates wide swings in salinity and is frequently seen schooling in shallow, still pools at low tide.