The direction and intensity of ecological impacts are dependent on the feeding method of the majority of fish in a water body.
The suppression of zooplankton populations due to zebra mussel filtration is thought to affect the feeding of some fish. This reduction of zooplankton in the water column may affect the growth of fish that are planktivorous at some point in their development (MacIsaac 1996).
When zebra mussels enter new habitats, they can quickly become a major component of the diet of molluscivorous fish. This has been documented for freshwater drum in Lake Erie (French and Bur 1993). Utilization of this new food source may lead to increased growth rates and productivity, and this has been documented in studies in the former Soviet Union (Poddubnyi 1966, Lyagina and Spanowskaya 1963, Zheltenkova 1949). Field studies by French and Bur (1996) suggest, however, that zebra mussels may not be of benefit to freshwater drum when serving as a staple in their diet.
In general, there is an enhancement of all benthic feeding fishes, even those that do not feed on Dreissena, because zebra mussels increase the biomass of other benthic invertebrates (Dermott and Munawar 1993, Griffiths 1993, Stewart and Haynes 1994, Karatayev and Burlakova 1995b, reviewed in Molloy et al. 1997).