ABSTRACT. – The diversity and structure of fish populations in southern Mediterranean lagoons are poorly documented. Spatial and temporal variation in uses of shallow habitats for fish fauna in Bizerte Lagoon in Tunisia was investigated in relation to environmental variables. Fish sampling was carried out over four seasons at four stations with a 3 mm mesh beach seine. Multivariate statistical analyses were applied to assess environmental influences (temperature, pH, salinity, dissolved oxygen) on fish spatiotemporal assemblages. A total of 3,612 individuals were collected representing 26 species from 14 families. The fish assemblage was quantitatively dominated by resident species, mainly the big-scale sand smelt Atherina boyeri accounting for 69.49 % of the total number of fish captured. The fish assemblage was largely dominated in terms of ecological guild by the marine migrant species and fish feeding groups belonging to microbenthivore and detritivore species. The Bizerte Lagoon functions as a coastal inlet, with euryhaline conditions throughout the year. Hydrological variables measured in the shallow waters were uniform across the whole lagoon and had low influence on the spatiotemporal fish assemblages. The lagoon could be of great importance in providing nursery habitats for juvenile marine migrant fish species.