FISHERY BULLETIN: VOL. 86, NO. 3 



becomes difficult to determine because of the inter- 

 mittent nature of the growth increments and the 

 variety of width-sizes (Fig. 4i). In large areas of the 

 otolith, increments appear to be absent or indeter- 

 minate, with a coarse underlying crystal structure 

 (Fig. 4j) making accurate determination of incre- 

 ment sequences difficult. However, the fine incre- 

 ments of the oreo otolith are 3 to 5 ^m wide, which 

 is within the range of daily growth increments 

 described for other species (Jones 1986; Gauldie in 

 press). 



Black Oreo Otolith 



The black oreo otolith is almost identical to that 

 found in the smooth oreo in overall shape, propor- 

 tion, structure, topography, surface and internal 

 crystallinity, and increment pattern. Some minor 

 differences do, however, exist. 



In the medial sulcus, the prominent knobs found 

 in the smooth oreo otolith are smaller than in the 

 black oreo. On the surface of the sulcus, large leaf- 

 like crystals having various orientations occur (Fig. 

 5a). Also present in the sulcus are porous, sponge- 

 like crystals adjacent to membranous structures 

 (Fig. 5b). Smooth patches, where crystals appear ab- 

 sent, occur on the lateral surface of the otherwise 

 coarsely crystalline irregular lobe (Fig. 5c). At 

 higher magnification the smooth patches are seen 

 to be smaller growth forms of the larger adjacent 

 crystals. 



DISCUSSION 



Despite some minor differences in topography and 

 crystallinity, the sagittae of both species are essen- 

 tially identical. The otoliths are structurally complex 

 v^ath a great variety of crystalline forms. The coarse 



Figure 5a. —Split-screen SEM of large leaflike crystals in the black oreo otolith sulcus. Magnification = 356 x and 979 x . 

 b.— Porous, sponge-like crystals in the otolith sulcus. Scale bar = 10 ^^m. 

 c. —Smooth patches on the central lateral surface of the otolith. Scale bar = 0.1 mm. 



512 



