Behavioural responses and habitat use of <i>Acanthopagrus schlegelii</i> in structurally enriched artificial environments

Acanthopagrus schlegelii is an economically important coastal species whose enhancement and aquaculture performance are closely linked to habitat conditions. However, habitat degradation has constrained its sustainable utilization. In this study, controlled laboratory observations were conducted using four individuals per trial, with each experimental group observed continuously for 24 h and three replicate groups established. Four habitat treatments were tested: artificial reef, artificial seaweed reef, artificial seaweed, and barren water control. Spatial distribution, residence time, and swimming path length were quantified. Habitat type significantly affected habitat selection and behavioral responses. Fish showed a clear preference for structurally complex habitats, with occurrence frequency in the artificial reef and artificial seaweed reef treatments markedly higher than in the artificial seaweed and barren water treatments. Temporal aggregation patterns also differed among habitats: fish tended to aggregate around the artificial reef in the early morning, whereas use of the artificial seaweed reef peaked around midday. Residence time was longer in structured habitats, especially at night, and swimming path length was greatest in artificial reef treatments, followed by artificial seaweed reef, while the barren control showed the lowest activity range. These results indicate that habitat structural complexity and spatial heterogeneity strongly regulate habitat selection and behavioral adaptation in A. schlegelii . They also provide practical support for the use of composite-structured habitats in aquaculture enrichment and artificial habitat design.