Transitional environments in deltaic areas comprise a mosaic of aquatic ecosystem resources, characterized by distinct biological communities and ecological functions that contribute significantly to human well-being. In the context of ecological quality, identifying reliable biotic indicators for assessing the conservation status and ecosystem services in these systems remains a challenge due to their high spatial heterogeneity and temporal variability.

This study explores the application of fish communities to describe the biotic characteristics of eight transitional wetlands in the Po Delta (Italy), as indicators for assessing their conservation status and ecosystem services (i.e., fisheries and habitat provision for species). Fish communities were used to characterize the compositional, structural, and functional status of ecosystem resources, based on both presence/absence survey data and local fish market records. The indicators were developed by calculating the Fish Habitat Biological Index (HFBI), taxonomic diversity metrics, and functional indices based on key life-history traits, namely habitat use and feeding mode.

The results indicate that fish-based indicators effectively discriminate between wetlands with different ecological conditions and service provision capabilities, capturing significant variations in both ecosystem structure and function. Overall, the study demonstrates that fish communities provide operational and policy-relevant indicators that can be directly integrated into ecosystem condition and ecological quality accounts of these environments, supporting the implementation of ecosystem accounting in transitional deltaic wetlands.