In Japan, the number of large floating cages (e.g., with a 30-m diameter) installed offshore for aquaculture purposes is set to increase. However, the behavior of fish schools in cages is not yet fully understood. In this study, we conducted continuous vertical observations of the behavior of yellowtail (Seriola quinqueradiata) in a cage for 16 days using broadband quantitative echosounders (EK80, WBAT, ES120-7CD, and ES200-7CD; KONGSBERG, Norway). Echograms were obtained for each transducer installed on the inner and outer sides of the cage. It was suggested that yellowtail schools were concentrated in the lower layer on the outer side of the cage during the day and were widely distributed at night. Moreover, the yellowtail were concentrated in the upper layer when the cage floated to the surface (i.e., feeding time). These results will be useful for building a monitoring system to detect abnormal behavior. Work supported by Cross-ministerial Strategic Innovation Promotion Program (SIP), “Building a Resilient and Nourishing Food Chain for a Sustainable Future” (Grant No. JPJ012287; funding agency: Bio-oriented Technology Research Advancement Institution).
Yamamoto et al. (2025) studied this question.