The effect of otolith malformation on behavior and cortisol levels in juvenile red drum fish (Sciaenops ocellatus)

Captive-raised red drum fish were observed with phenotypic abnormalities, including deformities of the spine, jaw, and cephalic region, that were consistent with vitamin C deficiency during the larval stage. In light of their visible exterior skeletal abnormalities, we suspected that the affected fish would also have abnormal otoliths. Otoliths are dense calcareous structures that function in fish hearing. We hypothesized that abnormal fish would have irregular otoliths that would alter behavior and cortisol levels as compared with those of phenotypically normal fish. The normal and abnormal fish had statistically significant differences in behavior, cortisol levels, and otolith volume and density. MicroCT assessment of abnormal fish revealed operculum abnormalities, malocclusions, and several types of otolith malformations. Therefore, the affected fish had not only an abnormal skeletal appearance but also significantly abnormal behavior and cortisol responses.