On this paper a description of a monitoring system for marine speciesbased on acoustic hydrophones and transmitters is presented. The main purpose of the work is to test the performance of these instruments working in a closed space, similar to the one found in the field where they will be installed. Transmitters are carried by the studied species, and the receivers are placed inside artificial reefs with the purpose to detect the presence of the species while they are inside. Results have shown that the hydrophone located farther away from the walls is the one with better performance, in relation to those installed close to the walls. The same behavior has been observed on transmitters, the one which is located in the center of the pond was better detected.