| Summary: | Japanese anchovy (<i>Engraulis japonicus</i>) is an economically important species found in the coastal waters of the northwestern Pacific Ocean. To conduct effective acoustic surveys on the spawning or fishing grounds of this species, the target strength (<i>TS</i>, dB re 1 m<sup>2</sup>) during its growth stages must be understood. However, knowledge regarding the <i>TS</i> of juvenile Japanese anchovies is limited. To address this knowledge gap, we measured the <i>TS</i> and proposed equation models for juvenile Japanese anchovies while describing the <i>TS</i> differences between young and adult anchovies. We evaluated 21 live anchovies using 38, 120, and 200 kHz transducers. <i>TS</i> models were fitted for the juvenile stage of anchovies, considering different frequencies. The mean <i>TS</i> values of young and adult anchovies were similar to those reported in previous <i>TS</i> studies, whereas the <i>TS</i> values of juvenile anchovies were significantly lower. Thus, applying the same <i>TS</i> equation based on the acoustic characteristics of anchovies at different growth stages, especially for juvenile anchovies, may not be appropriate. These findings underscore the importance of adopting a suitable <i>TS</i> equation specific to the growth stages of Japanese anchovies for accurate data analysis in acoustic surveys conducted on spawning and fishing grounds.
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