Intraspecific Variation in Gulf Killifish ( <i>Fundulus grandis</i> ) Avoidance of Contaminants

Abstract Understanding the behavioral response of estuarine fish populations to environmental contaminants is critical for assessing the ecological consequences of disturbances. Here, we examined population-level variation in avoidance behavior to petroleum-contaminated sediments in the Gulf killifish ( Fundulus grandis ), a sentinel species in northern Gulf of Mexico marshes. Adult fish were collected from four geographically distinct estuaries—Terrebonne Bay, Louisiana; Mississippi Sound, Alabama; Pensacola Bay, Florida; and Cedar Key, Florida. Choice experiments tested fish preference to either uncontaminated sediments or sediments contaminated with fresh or weathered oil. Results found significant differences among populations with individuals from western Gulf sites (Louisiana and Alabama) exhibiting strong avoidance of fresh oil, while those from eastern sites (Florida) showed limited or no avoidance. No populations avoided weathered oil. These findings suggest that sensitivity to oil contamination varies regionally, potentially reflecting local exposure histories or environmental adaptation. The diminished response to weathered oil across all populations highlights a reduced ability to detect residual contamination and indicates that these fish may use more volatile compounds that precipitate or degrade faster as a cue. This study underscores the importance of incorporating behavioral and population-level variability into impact assessments and emphasizes the need for regionally tailored conservation strategies.