In Tunisia, freshwater fishery resources have just recently been exploited in comparison to sea fishing. Nonetheless, despite its recent history, the sector has garnered considerable attention. To ensure its durability and development, reservoirs have been filled with various types of fish fry gathered from coastal and estuary zones. Fish populations’ stock assessment in reservoirs is also crucial for the sustainable management and conservation of ichthyologic freshwater resources. To assess the evolutionary trends of the fish resources available in the Siliana and Kasseb reservoirs, located in the Siliana and Beja governorates respectively, the Higher Institute of Fisheries and Aquaculture of Bizerte, in collaboration with the Aquaculture Technical Centre and the General Directorate of Fisheries and Aquaculture, carried out the present study. For sampling the researchers used multi-mesh nets regarding the European Standard CEN prEN 14,757, which are designed to capture most fish sizes in the reservoir water column. All of the outcomes of the fishing operations were converted into yields (number of fish) per unit of effort and were then entered into a Geographic Information System to map the results, allowing for the proposal of scenarios for improving stock status. The inventory settlement included six species: mullet, rudd, roach, pikeperch, and common carp, which are variably distributed. Our findings showed that the yield of these species is moderate in Siliana when compared to prior studies in terms of weight and on the digital map (23.72 ind/1000 m2 and 4.7 kg/1000 m2), while yields in Kasseb Reservoir are found to be quite low (123 ind/1000 m2 and 18 kg/1000 m2). The statistical analysis demonstrates that Siliana Reservoir possesses a high abundance of mullet population. Indeed, this reservoir is endowed with more effective habitat conditions than Kasseb, favouring the growth and survival of rudd and roach. In addition, the mapping of the distribution of different species and catch rates in these two reservoirs shows that the studied populations are diverse. The study also revealed that some ecological niches in the dams are underexploited, which requires certain measures to be undertaken, such as boosting fishing operations, seeding Mugilidae fry and introducing new species. The authors thus recommend that the various actors in the fishing sector take concerted action in this regard.