The neuraminidase‐producing ability of bacteria from coastal fish intestines and their environments was determined using a fluorogenic substrate, 2′‐(4‐methylumbelliferyl)‐α‐d‐N‐acetylneuraminic acid. Of 836 isolates examined, 758 (90·7%) produced little or no neuraminidase (< 0·0002 U ml⁻¹) while 78 (9·3%) produced ≥ 0·0002 U neuraminidase ml⁻¹. Of note, 10% of vibrios from fish intestines could produce neuraminidases, and 9% did it efficiently. This result suggests that the vibrios capable of producing neuraminidases are able to colonize and establish in the intestinal tract of coastal fish to some extent. Additionally, as many as 58% of the Vibrio isolates with high abilities were tentatively identified as Vibrio damsela.