Fish sounds

This research presents findings from an in-situ experiment utilizing a hydrophone line array to capture the sound production of the Goliath grouper. Analysis revealed that Goliath grouper calls exhibit multiple frequency components, including one high-amplitude component and 2 to 3 low-amplitude components. The primary high-amplitude component is concentrated in the 30 to 70 Hz band, peaking around 50 Hz, while low-amplitude components span 20 to 30 Hz, 70 to 115 Hz, and 130 to 200 Hz. Comparison between in-situ data and results from a normal modes transmission loss model identified regions where echo level increased with propagation distance. This suggests that the loudness of the call may not necessarily indicate proximity, indicating the Goliath grouper might rely on other cues for localization, such as changes in the frequency profile of its call. Two methods for estimating call distance are presented. The first method vi utilized a transmission loss model and measured transmission loss across a hydrophone line array. This method could also determine the source level of the calls, yielding source level estimates ranging from 124.01 to 144.83 dB re 1 μPa. The second method employed match field filtering, validating the accuracy of the transmission loss model. Both methods produced similar call distance estimations, ranging from 11.5 to 17.1 meters, placing the grouper inside or near its typical habitat.

The sound producing mechanisms of Chilara taylori (Girard)
and Ophidion grayi (Fowler) are sexually dimorphic. These
mechanisms involve the airbladder, a modified anterior axial
skeleton and three pairs of muscles; all have an enlarged
first vertebra and a pair of similarly modified and enlarged
first ribs. In the male Chilara taylori, two thin convex
bones are embedded in the anterior face of the airbladder.
Slits are present in the lateral wall of the airbladder just
behind the embedded bones. The male Ophidion grayi has a
very rigid airbladder. Highly modified third ribs shaped like
inverted ram's horns are embedded in the airbladder wall.
These ribs encircle a membranous area in the anterior of the
airbladder in which a median rocker bone is embedded. The
sound producing mechanisms of the females of both species lack
specialized bones associated with the airbladder. Their
sound producing mechanisms are not as well developed as in
the male.