California Killifish Identification Guide

Key identification features

• Stocky, moderately elongated body up to about 9-10 cm, larger than many freshwater killifish relatives
• Coloration is olive-brown to greyish above, fading to silvery on the sides and belly
• Faint vertical barring may appear on the flanks, especially in breeding males
• Small, upturned mouth and a broad, flattened head adapted for surface and shallow-bottom feeding
• Rounded caudal fin without lyretail extensions, and a dorsal fin set toward the rear of the body
• Breeding males often show a subtle yellow-orange tint on the fins, while females stay plainer and greyer

Common look-alikes

• Diamond Killifish: much deeper and more compressed, giving a rhomboid rather than elongated body shape
• Blackstripe Topminnow: found only in central/eastern freshwaters and shows a solid dark lateral stripe absent in California Killifish
• Golden Topminnow: eastern species with golden flecking, not found in Pacific coastal habitats

Where you'll see one

Restricted to coastal California and northern Baja California, this species lives in salt marshes, tidal sloughs, and brackish lagoons, tolerating wide salinity swings from nearly fresh to full seawater. It is commonly seen schooling in shallow, still pools left behind as the tide recedes.