Analyzing the response of grass carp larvae to acoustic stimuli using particle tracking velocimetry.

Abstract:

As damage on aquatic ecosystems caused by invasive species increases, different types of barriers have been studied to prevent the introduction and further spread of invasive species in endangered areas. Monitoring and control of grass carp to prevent them from reaching the Great Lakes is a timely example of such efforts. Sound is a typical non-physical barrier which injects traveling pressure waves as a stimulus. In this study, we analyzed how grass carp larvae respond to a range of sound frequencies, capturing their movements with a camera, and identifying their trajectories via particle tracking velocimetry (PTV). Larvae were detected from the images based on pixel intensities and their trajectories were tracked by quantifying the similarity of movements between two consecutive frames. To define whether each carp larvae actually responded to the sound, we computed their instantaneous velocity and acceleration to analyze how these two quantities shifted as the stimulus began.

In general, approximately 100 larvae were detected from PTV analysis for each experimental case. The number of larvae that showed a sudden jump of velocity and acceleration were counted to compute the percentage of larvae responding to the sound. The result showed changes in the proportion of larvae responding to the sound as sound frequencies were changed from 100 to 1000 Hz. The highest response was found at 700 Hz, which indicates that corresponding frequencies can generate the most effective condition to alter larvae movements. We conclude that PTV analysis can be applied to determine the response of larvae to sound in natural environments. We expect that our analysis can be incorporated in multidisciplinary approaches to improve control strategies to address the complicated problems caused by invasive species.