Call properties of the large yellow croaker (Larimichthys crocea) during reproduction with insight into directivity.

The investigation of the large yellow croaker (Larimichthys crocea) deserves more attention due to its high commercial value as an important aquaculture fish species. This study was initiated by deploying a passive acoustic monitoring device to record the calls from the L. crocea during the spawning process in an aquaculture facility. The subsequent analysis suggested the croakers produced at least two types of calls with considerable energy distributed up to 1000 Hz. The acoustic data and the computed tomography scanning of an adult croaker were used to develop a numerical model to address the directivity of the calls at frequencies up to 1000 Hz. The radiation patterns at all frequencies were assigned with respective weights and then combined to estimate an overall acoustic radiation pattern for both types of the calls. The backward transmission was greater for both types of calls by 1.85 dB on average. The reduction of size by 20% in the swim bladder resulted in a stronger sidelobe in the frontal direction, indicating its influence on call directivity. These results provided information on the directivity of the croaker calls and understanding of fish acoustics.