Fishes are expected to interact with Marine Renewable Energy (MRE) projects in ways dependent upon both the nature of the project in question and on the ecology of the species considered (Figure 1). The siting of MRE projects will determine the habitat affected, the species expected to encounter the project, and the length(s) of associated cables. The nature of the technology will limit the variety of interactions possible: For example, a tethered wind turbine with few or no moving parts below the surface offers a reduced suite of potential interactions than does a wave energy conversion device with subsurface moving parts. Underwater noise and vibrations, chemical coatings, lubricants and hydraulic fluids, electrical insulation, the depth to which transmission cables are buried, and even color choices for subsurface structures could all affect the nature and extent of ecological effects. Assuming that fishing activities are limited in the vicinity, these projects may function as de facto marine reserves, with effects on both fish populations and area fisheries. The ecology and biology of the diverse species contribute further to the array of interactions. Pelagic or open water species may visit these projects as sources of food, preying on smaller fishes or invertebrates associated with the structures. In tropical waters, such devices would undoubtedly function as Fish Aggregation Devices (FADs); in colder waters, associated fish assemblages may aggregate according to different behavioral/ecological mechanisms. FADs and flotsam assemblages in the tropics are typically dominated by scombrids and carangids, but these taxa are less diverse in temperate waters and have not been reported to associate with flotsam at higher latitudes. Nonetheless, there is a great deal that remains to be learned about flotsam-associated fishes, and the phenomenon should not be ruled out in the case of MRE projects. Migrating species, particularly those that travel along the coast, may be expected to encounter these projects. Salmonids generally and, along the West Coast of the United States, green sturgeon (Acipenser medirostris) in particular are migrating species likely to encounter offshore projects, at least in the form of their associated cables to facilities on shore. Potential interactions include concentration of predators, EMF effects, and the loss of foraging habitat. Reef species are expected to treat these structures as reef-like habitat, and a resource for foraging, shelter, spawning and more. The structural complexity of a MRE project may be analogous to the factors affecting the efficacy or appeal of an artificial reef (for example, see Bohnsack et al. 1991 and Perkol-Finkel et al. 2006). Fishes associated with soft bottom habitats may be locally displaced, although some of these species do occupy the ecotones between natural reef and soft bottom habitat; these projects may offer these fishes additional habitat. Finally, fishes may respond by avoiding these structures, by actively associating with them, or by showing no behavioral response at all. Recent studies have focused on baseline research, sampling potential project sites and control areas to anchor before-after-control-impact (BACI) studies once projects are established. Additional research on the response of fishes to electromagnetic fields, artificial reefs, and FADs would considerably improve our capacity to assess the potential effects of MRE on fishes. Baseline studies designed to form the foundation of a BACI study, research on fish assemblages around existing offshore analogues (e.g., oil platforms, navigational buoys, etc.) and the development of vigorous and effective citizen science programs are strongly encouraged.