Acoustic researches were made in the Miramare Marine Reserve (Gulf of Trieste, Adriatic Sea, Italy) and just outside it in order to evaluate interferences between fish acoustic communication and man-made under- water noise due to the passage of outboard engine boats. Average sea ambient noise was recorded both inside and outside the protected area because in the reserve the passage of boats is intermittent, while outside the boat traffic is intense. Then observations in tanks and in the field were made on the territorial agonistic behaviour of the red mouth goby Gobius cruentatus, a benthic fish present in and out the protected area. Two different fish sounds were recorded: a train of distinct knocks and a drumming sound, a less regular spaced train. The frequency range is from 50 Hz up to 800 Hz with highest amplitude below 200 Hz. Meanwhile the boat noise was recorded from the smaller distance between engine source and fish inside (200 metres) and outside (10 metres) the preserved area. Finally all of these recordings were compared in a frequency - P.S.D. graph. The result of the comparison suggests that in the Reserve the acoustic communication in G. cruentatus is undisturbed and that this approach is a useful method to assess and prevent the impact of man-made noise in a protected area.