Extreme variations in skull density of toadfish, Opsanus ta

Abstract

Gross observations of the skull in sexually mature toadfish revealed variations in bone density that appear to be most extreme in the otic capsule. Four male and one female toadfish (17–30.5 cm SL) were scanned to obtain images formatted at 100 μm and 1 mm. Consecutive measurements were made from caudal of the otic capsule to the rostral edge of the otic capsule. Attenuation values were recorded from three sites on the skull (left parietal bone, parietal suture, ventral surface of the otic capsule) and along two otoliths (calcareous, associated with the sensory epithelia of the ear) within the otic capsule. In all five fish, the parietal suture had the highest attenuation. Attenuation values for the parietal bone varied with size, indicating increasing density with growth. Among all five fish, the lowest attenuations were obtained for the ventral wall of the otic capsule, with values similar to those of cartilage. In addition, the minimum values were found ventral to the saccular otolith. Given that the saccule is the primary auditory endorgan in this species [Edds-Walton et al., J. Comp. Neurol. 411, 212–238 (1999)], the co-occurrence of bone thinning in this area of the skull may have functional significance related to audition.