Diet composition, diet similarity, and major predator–prey interactions between the 15 most abundant demersal and pelagic fishes (N = 12,163 stomachs) during the period 1999–2003 were described for Northumberland Strait, a semi-enclosed, marine coastal ecosystem. Of the five pelagic species, Rainbow Smelt Osmerus mordax ate benthic prey (shrimps and polychaetes); Atlantic Herring Clupea harengus ... [Show full abstract] and American Shad Alosa sapidissima consumed small copepods and crab zoeae; and Atlantic Mackerel Scomber scombrus and Alewives Alosa pseudoharengus ate small copepods and moderate amounts of benthic prey and small fishes. Three demersal species were strongly piscivorous but with minimal diet overlap: Sea Ravens Hemitripterus americanus consumed small benthic fishes (especially flounders); Winter Skate Leucoraja ocellata consumed sand lances Ammodytes sp. and Rainbow Smelt; and White Hake Urophycis tenuis consumed Atlantic Herring and Atlantic Mackerel. Cluster analysis revealed seven feeding guilds, of which four contained a single species; consequently, the potential for compensation of predatory function was nonexistent for these guilds. The three multispecies guilds comprised consumers of (1) small copepods and crab zoeae; (2) small benthic invertebrates and polychaetes; and (3) shrimps and crabs. Based on diets, the principal route of energy transfer seemed to be the benthic–detrital pathway; however, confirmation requires representative abundance estimates for the various fishes. Moreover, abundances of many fish species have changed (i.e., most have decreased) since this study was completed, with unknown consequences for food web structure and functioning.