Sound characteristics of big-snout croaker, Johnius macrorhynus (Sciaenidae).

The sounds of a big-snout croaker, Johnius macrorhynus, produced under hand-held and voluntary conditions (in a large aquarium and in the field) were compared. Voluntary calls included "purr" and "dual-knocks", only purrs were produced when the fish was hand-held. The purr is composed of pulses in which the first interpulse interval was six to nine times longer than the other interpulse intervals, which were approximate in duration, and is a unique sound type in the coastal water of Taiwan. Purrs emitted under these conditions did not differ significantly, suggesting that the hand-held sound can be employed to match the sound in the field. These sounds contained energy reaching 5 kHz, with two peaks at about 1 and 2 kHz-the former being the dominant frequency. First interpulse interval, main interpulse interval, repetition rate of pulse, and pulse duration may serve as the diagnostic characters for the species-specific sound (i.e., purrs). One specimen survived in a large aquarium for 6 months and its vocal activity was monitored. The fish produced fewer dual-knocks than purrs, and purrs were about 11 dB louder than dual-knocks emitted in the aquarium. The temporal sequential relationship of these types in the sound of this individual was described.