ALFISH is a model created under the Across Trophic Level System Simulation (ATLSS) Program of the U.S. Geological Survey (USGS). Its purpose is to describe fish functional groups in freshwater marshes of the greater Everglades area of southern Florida. In particular, it is intended to assess the spatial pattern of fish densities through time across freshwater marshes. This model has the capability of providing a dynamic measure of the spatially explicit food resources available to wading birds. ALFISH simulates two functional groups - large and small fish - where the larger fish can prey on the smaller fish. Both functional groups are size-structured. The marsh landscape is modeled as 500-m x 500-m spatial cells on a grid across southern Florida. The ATLSS High Resolution Hydrology model is used to provide water levels in the spatial cells on 5-day intervals. Fish populations spread across the marsh during flooded conditions and either retreat into refugia (alligator ponds), move to other spatial cells, or die if their cell dries out.

ALFISH has been applied to the evaluation of alternative water regulation scenarios under the Central and South Florida Comprehensive Project Review Study. The objective of this Review Study has been to compare alternative methods for restoring historical ecological conditions in southern Florida. ALFISH has provided information on which hydrological scenarios are most likely to increase fish biomass and its availability to wading bird populations. The model also provides the opportunity for stakeholders with interests in particular subregions of the landscape to contrast the effects of alternative hydrologic plans on the availability of fish biomass in these subregions. As a demographic model, ALFISH also keeps track of the history of the effects of dry, normal, and wet hydrologic conditions on fish population size structure.