Jahnavi Mehta, Gowri K Uggini
Characterizing anthropogenic noise pollution in aquatic environments is inherently complex due to the multifaceted physical properties of acoustic waves, including variations in sound intensity, frequency, wavelength and temporal pattern. Among these parameters, contribution of specific frequencies, which are an integral component of broader noise spectrum remains poorly understood. To isolate the influence of this specific variable from overall complexity of underwater sound exposure, the present study employed Danio rerio as a model for aquatic developmental health and systematically investigated the effects of three distinct acoustic frequencies on early embryonic development. Different groups of fertilized eggs were exposed to either 40 Hz, 174 Hz or 528 Hz frequencies for 90 min daily, from 0 to 10 days post-fertilization, inside a soundproof acoustic box. Exposure to the low frequency sound waves i.e. 40 Hz, induced several statistically significant detrimental effects, like increased mortality, morphological abnormalities such as tail kinks, pericardial and yolk-sac edema, skeletal defects, histopathological changes in heart and eye regions, stunted growth, elevated oxidative stress and apoptosis. In contrast, 174 Hz frequency appeared largely benign, with no significant adverse effects observed across all developmental, morphological and physiological parameters. The 528 Hz frequency did not cause overt morphological damage, mortality or significant apoptosis. However, it induced a modest increase in GST activity. Overall, these findings identify low frequency sound as discrete drivers of noise-induced stress and provide critical evidence for environmental risk assessment. Also, the study highlights the need for further investigation of frequency-specific safety thresholds for vulnerable early-stage aquatic organisms.