In this study, we examined bioenergetic responses of age-2+ and age-3+ mummichogs (Fundulus heteroclitus) to degraded habitat condition and impoverished benthic prey community in polluted salt marshes by incorporating in situ food consumption rates with the mercury mass balance model technique. In general, bioenergetic responses of mummichogs appeared to be more related to benthic prey community than habitat condition. Fish from prey-impoverished marsh (PIM) sites generally had significantly elevated total metabolic costs compared with those from non-prey-impoverished marsh (NPIM) sites. However, the PIM populations also had ~two- to three-fold higher consumption rates than the NPIM populations, suggesting that the PIM populations may be capable of adjusting food consumption to offset elevated metabolic costs. Furthermore, only age-2+ females of the PIM populations had significantly reduced growth rates, whereas there was little among-site differences for age-2+ males and age-3+ fish, indicating that an increased consumption by the PIM populations may also have been a compensatory mechanism to maintain growth. Most of the PIM populations, however, had substantially (up to 80%) lower growth conversion efficiency relative to the NPIM populations. These findings suggest that pollution-tolerant fishes such as mummichogs may have energetic costs of living in chronically degraded habitats.