In this study, the drying experiments were conducted on fresh fingerlings of Nile tilapia, which does not benefit the consumers (non-marketed and juvenile fish), for production of the fishmeal to be used as an ingredient in feedstuffs in the aquaculture, dairy, and poultry industries. The thin layer drying behaviour of Nile tilapia fingerlings was experimentally investigated in a mechanical dryer and the mathematical modeling by using two thin layer drying models (simple and modified simple exponential models). The butane-gas was used as heat energy source for the dryer. The impact of the drying air temperature (50, 60, 70 and 80oC) and hot air velocity (0.5, 1.0 and 1.5m/s) on the fish moisture losses against drying time has been studied. Drying rate, moisture ratio, cost estimation and microbial assays of the drying process were also considered. The obtained data showed that, the shortest drying time of the fish was recorded at 140min with 80oC drying air temperature and 1.5m/s air velocity. While, the longest drying time was recorded at 280min with 50oC and 0.5m/s treatments. Tilapia moisture content decreased from an initial level of about 84.56%(d.b.) to range between 9.18 and 11.86%(d.b.) at the end drying process depending on the drying conditions. Moreover, drying rate was increased with the increase of drying air temperature and air velocity. Between the two tested models, the modified simple exponential model was found to be the most suitable for describing the drying behavior of the fish. The effects of drying air temperature and velocity on the drying constant and coefficient were also shown. On the other hands, the calculated operation cost of the dryer approaches about 2.88LE/kg of dried whole fish. Also, the final product had a microbial count below allowed level.