There is much evidence supporting the idea that pelagic larvae of coral reef fishes are active participants in their dispersal and return to a reef, however, the mechanisms used to navigate are still uncertain. It has been proposed that sensory cues, such as hearing, play a role. Sound is a potentially important cue for organisms in marine environments, especially in noisy environments like coral reefs. Sensory organs, including otolithic organs, of most coral reef fish form within the first few days of life. The auditory brainstem response (ABR) technique was used to measure hearing on a wide size range of sergeant majors (Abudefduf saxatilis). Complete audiograms were measured for 32 fish ranging in size from 11-121 mm. Significant effects of standard length on hearing thresholds at 100 and 200 Hz were detected. At these lower frequencies, thresholds increased with an increase in size. All fish were most sensitive to the lower frequencies (100-400 Hz). The frequency range that fish could detect sounds was dependent upon the size of the fish; the larger fish (>50mm) were more likely to respond to higher frequencies (1000-1600 Hz). A. saxatilis have poor hearing sensitivity in comparison to audiograms of other hearing generalists including other species of Pomacentrids. Due to the high hearing thresholds found in this study in comparison to recorded ambient reef noise, it is unlikely that sound plays a significant role in the navigation of the pelagic larvae of sergeant majors to the return of the reef from large distances.

Objective: The aim of this study was to compare cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP) in young gender- and age-matched black African and Caucasian male and female adults. Design: A quasi-experimental between-subjects research design was utilised. This study was comparative in nature, thus data was collected in a cross-sectional manner from two age- and gender-matched racial groups, namely black African and Caucasian, and compared. Furthermore, interactions of gender and race were also examined in this research study. Methods: Sixty healthy age- and gender-matched participants (30 black African, 30 Caucasian) between the ages of 18 25 years participated in this study. Fifteen males and fifteen females, within one year of the age of their racial participant counterparts, were included in each racial group. Latencies, peak-to-peak amplitudes and asymmetry ratios were analysed for both groups in these tests. Furthermore, auditory brainstem response (ABR) and electromyography (EMG) testing were conducted to investigate whether possible racial differences in VEMP tests could be attributed to differences in neural or muscular function. Results: Black African participants demonstrated significantly shorter latencies of the n23 component of the cVEMP and the p15 component of the oVEMP, as well as larger peakto- peak amplitude of the oVEMP response. Highly significant differences were found in all EMG measurements between the two racial groups, suggesting that these racial VEMP differences are primarily based on differences in muscular function between black Africans and Caucasians. Significant gender differences were observed in all tests conducted, with females predominantly displaying shorter latencies, while males had larger amplitudes. Conclusions: Young black African adults demonstrated significant differences in both cVEMP and oVEMP responses, namely shorter latencies and larger amplitudes, in comparison to young Caucasian adults. Correlations with differences in EMG measurements suggest that these differences are primarily due to differences in muscular function as opposed to neural function. Future research is required to confirm and expand on these findings. / Dissertation (MCommunication Pathology)--University of Pretoria, 2016. / Speech-Language Pathology and Audiology / MCommunication Pathology / Unrestricted