Aims: The objectives were to count and identify the oil-utilizing bacteria associated with fish, and to study their hydrocarbon-degradation potential. Methods and Results: The standard dilution-plate method using a medium with crude oil as a sole source of carbon and energy revealed that 10 different fish sorts from the Arabian Gulf and two from fish farms accommodated millions of oil-utilizing bacteria per square centimetre of fish surface and per gram of gills and guts. According to their 16S rRNA sequences, those bacteria were affiliated to Psychrobacter, Vibrio, Planococcus, Pseudomonas and Actinobacterium. Planktonic and benthic biomass samples from the Gulf were also rich in oil-utilizing bacteria, but with different composition. All isolates could grow on n-alkanes from C-8 to C-40 and three representative aromatics as individual sole sources of carbon and energy. Quantitative analysis of hydrocarbons by gas-liquid chromatography revealed that the biomass samples of the individual bacteria could consume crude oil, n-octadecane and phenanthrene in liquid media. Conclusions: The abundant oil-utilizing bacterial associated with fish have the potential for cleaning oily waters. Significance and the Impact of the Study: Aquatic fauna accommodates rich consortia of oil-utilizing bacteria.