DAVIES ET AL.: OTOLITH ULTRASTRUCTURE OF SMOOTH AND BLACK OREO 





Figure la. —Relative positions of the otoliths in the right endolymphatic sac (ENS) of the smooth oreo in lateral view: astericus (AS), 

 lapillus (LA), and sagitta (SA). Anterior (A), dorsal (D), posterior (P), and ventral (V) surfaces are indicated. Magnifi- 

 cation = 6.3 X. 



b. —Dorsal (regular) and ventral (irregular) lobes of the otolith in lateral view, nucleus (N), sulcus (S), and rest as in Figure 



la. Magnification = 12.5 x. 



c. — SEM of the lateral surface topography of the otolith. Scale bar = 1 mm. 



ground surface was polished with 2000 grit wet and 

 dry paper to yield a smooth surface for etching. The 

 most successful results were obtained by etching 

 with a 0.1 M solution of disodium salt of EDTA. The 

 otoliths were immersed in this solution for 15 to 20 

 minutes. Other suitable etching solutions employed 

 were 1) a 1% solution of HCl for 20 to 30 seconds 

 and 2) a 2% solution of Histolab RDO (a commer- 

 cial etching solution comprising a mixture of HCl 

 and EDTA) for 5 minutes. A cellulose acetate peel 

 was made of the etched surface to obtain an exact 

 replica of the surface features. The peel was placed 

 on a microscope slide under a cover slip, cleared with 

 ethanol or distilled water, viewed, and photographed 

 using a Zeiss photomicroscope. Direct observations 



of thin sections (about 20 ^m) of otoliths did not 

 show any more information than that observed in 

 acetate peels. Acetate peels had the advantage of 

 allowing successive grinds to be examined thereby 

 avoiding the problem of losing information that 

 might be located only in very narrow layers within 

 the otolith. 



Scanning electron microscope (SEM) photographs 

 were taken of otoliths using a Phillips 505 SEM. 

 Whole otoliths were glued on to SEM pin type 

 mounts, cemented in position with contact cement, 

 and sputter-coated with gold at approximately 5 

 Torr. The external surface topography of both the 

 medial and lateral faces of the otoliths was photo- 

 graphed. Selected pieces of otoliths broken by thumb 



501 



