One of the fish species that is most frequently transported alive in Europe is rainbow trout Oncorhynchus mykiss. Conditions before and during the transport have a significant impact on the fish’s health, stress response, and final product quality. Water quality deterioration during transport is unavoidable, despite starvation periods and water changes before the shipment. In transport water, hazardous ammonium and carbon dioxide concentrations increase. Improved water conditions during a transport can be achieved by applying additional filter technology. Mobile immersion filters developed at AWI have been tested to control ammonia and carbon dioxide concentrations during the transport of fish. The related scientific research achieved notable results when applying the Mobile Immersion Filter (Patent DE102019122146B3), these results are summarized below. Initially, three different design concepts for immersion filters were evaluated for the capability to lower ammonia and carbon dioxide in transport water of fish. Results are focused on ammonia reduction with ammonia reduction compared to a control being evaluated as technical proof of concept . Transport boxes for fish were used and prepared by adding ammonium chloride as a solution of 12 mg/L to the water. After 9 hours, a very substantial difference was detected between tanks with a Mobile Immersion Filter (MIF) and controls, with the dissolved ammonium level in the water of the transport tanks decreasing to 3 mg/Liter with a MIF. Although all models functioned admirably, model A2 (Patented version) was chosen for controlled experiments with tanks for fish transport containing 50kg of live rainbow trout Oncorhynchus mykiss and 500 liters of water per tank. A transport was simulated for four hours with ammonia determined every hour. The results demonstrate that ammonium generation in the control tanks was approximately 50% greater than the experimental tanks with MIF. These results are highly valuable due to the critical role of ammonium in long-term transport