FISHERY BULLETIN: VOL. 86, NO. 3 



pressure were examined and photographed to ob- 

 tain internal structural information. Finely ground 

 cross-section surfaces were also polished and etched 

 for examination with the SEM. 



RESULTS 



Smooth Oreo Otolith 



The sagitta is clearly divided into two distinct 

 structures: a small, smooth, regular dorsal lobe and 

 a larger, irregular ventral lobe (Fig. lb). The irreg- 

 ular lobe has branched crystal formations and clefts 

 at the ventral edge. The lateral face topography is 

 complex (Fig. Ic). The central bumpy area contains 

 the nucleus between the two lobes. Radiating out- 

 wards from the nucleus are concentric ridges on the 

 antisulcul surface. 



The crystal morphology of the lateral surface of 

 the sagitta is variable. Over much of the central 

 parts of the sagitta, large and variably oriented 



crystals give a coarse appearance to the surface of 

 the otolith (Fig. 2a) which presumably obstructs, by 

 diffraction, potentially clear zones in the whole 

 otolith viewed by transmitted light. At the edge of 

 the regular lobe, the crystal type alters to form slabs 

 of crystal layers (Fig. 2b). The analogous area on 

 the irregular lobe yields variable crystalline struc- 

 tures with complex alignments (Fig. 2c). Deep 

 troughs and branching furrows break up the crystal 

 forms at the edge of the irregular lobe. 



The medial surface has three distinct parts: the 

 central sulcal area, the edge of the irregular lobe, 

 and the edge of the regular lobe (Fig. 3a). Raised 

 ridges and two prominent knobs are found in the 

 central sulcal area. Crystals compacted into a petal- 

 like growth pattern are found in this part of the 

 otolith (Fig. 3b). Contrasting to this, more porous 

 crystal structures occur in the edge areas of the 

 regular lobe (Fig. 3c). Further variety is found on 

 the irregular lobe, where a very porous, honeycomb- 

 like crystal arrangement exists (Fig. 3d). At the 



Figure 2a. —Coarse crystal structure of the central lateral surface of the smooth oreo otolith. Scale bar = 0.1 mm. 



b. —Split-screen SEM of the transition of the crystal-type at the edge of the lateral surface of the regular 



lobe. Magnification = 163 x and 652 x. 



c. —Haphazard crystal alignments at the edge of the lateral face of the irregular lobe. Scale bar = 0.1 mm. 



502 



