For the development of acoustic fishing method, we had been researched a fundamental study which concerned on the sound production and behaviour of crabs was conducted. For specimen crabs such as Portunus trituberculatus and Charybdis japonica were selected. Croaking noise were recorded by the Cassette-recorder (Sony model CF-1600) through the under water monitor microphone, and analyzed in frequencies by Octave band analyzer, Rion SA-55, and sound pressure level of source by sound level meter, SM-5844. The following are the results obtained from the present investigations : When sound production of crabs (Portunus trituberculatus( female ) : carapace width $12.6~15$cm) were attracted to another crabs in the water of anechoic aquarium, efficacy of phonotaxis was $84~100\%$ and velocity by phonotaxis was $6.5~7.2cm/sec$. The time required for copulation ranged from 90 minute to 95 minutes by Charybdis japonica, at that time there was no sound production with their copulation.