Introduction
Understanding sound propagation patterns in controlled aquatic environments is a critical prerequisite for the accurate interpretation of biological and behavioural data in experimental studies on aquatic organisms. Unlike open natural waters, confined systems such as aquaria generate complex acoustic fields due to limited dimensions, boundary reflections, standing waves, and resonance effects. These factors often lead to spatially heterogeneous sound pressure distributions, which are frequently overlooked in laboratory-based behavioural research. The increasing use of acoustic stimuli in experimental studies has intensified the need to characterize the acoustic landscape within experimental tanks. However, many studies implicitly assume acoustic homogeneity without empirical verification. Adopting a geographical–environmental and interdisciplinary perspective, the present study aims to analyse the spatial distribution of sound pressure levels within an experimental aquarium. Specifically, it investigates the spatial variability of sound pressure across the upper, middle, and lower layers of the water column under two conditions: active sound treatment and silence. The primary objective is to assess the degree of acoustic heterogeneity and its implications for experimental design, environmental management, and the interpretation of behavioural responses in aquatic organisms

Materials and methods
The study was conducted in a standard laboratory aquarium equipped with an external loudspeaker positioned outside and adjacent to one lateral wall of the tank. The sampling design was developed to provide comprehensive spatial coverage of the aquarium volume. The water column was divided into three vertical layers—upper, middle, and lower—and sound pressure levels were measured at a total of 144 predefined spatial coordinates. Measurements were carried out under two distinct experimental conditions: with the sound source active and under silent conditions. All recorded acoustic data underwent preliminary quality control and processing. Spatial analysis techniques were then applied to visualize and interpret sound pressure distributions. Three-dimensional graphical representations were used to identify spatial gradients, zones of sound energy concentration, and variations associated with depth and horizontal position within the tank.

Results
The results demonstrated that activation of the sound source produced a highly heterogeneous acoustic field within the aquarium. The highest sound pressure levels were consistently recorded near the wall adjacent to the loudspeaker and in the lower layers of the water column, where sound pressure reached approximately 110 dB re 1 µPa. In contrast, sound pressure levels decreased markedly toward the central regions of the aquarium, with values declining to around 96 dB re 1 µPa, particularly within the middle layer. These findings indicate the formation of pronounced spatial gradients extending from the sound source toward the centre of the tank, as well as a strong interaction between depth and horizontal position in shaping the acoustic field. Under silent conditions, sound pressure levels remained relatively uniform and stable across all spatial locations and depth layers, with no substantial spatial variability observed.

Discussion
The findings of this study challenge the common assumption of acoustic uniformity in laboratory aquaria and highlight the potential for significant spatial bias in behavioural and physiological experiments involving sound exposure. The pronounced heterogeneity of the acoustic field under active sound treatment suggests that experimental organisms may experience substantially different sound pressure levels depending on their position within the tank. From an environmental and cross-sectoral development perspective, these results underscore the importance of incorporating acoustic considerations into the design, management, and regulation of controlled aquatic environments, including research facilities and recreational or display aquaria. Ensuring environmental sustainability, animal welfare, and scientific validity requires systematic monitoring and documentation of acoustic conditions. This study emphasizes the need to integrate soundscape assessment into experimental protocols and environmental management strategies to improve the reliability of behavioural studies and support informed decision-making in aquatic environmental planning