Toole et al.: Otolith microstructure, microchemistry and early life history of Microstomas paaficus 



745 



Figure 15 



Left otolith of 65.0-mm Stage-4 Dover sole Microstomus paaficus larva collected on 

 17 March 1989: anterior to left. Note stress checks, which are clearest in the ante- 

 rior field behind the anti-rostrum. Magnification = 50x. 



Discussion 



Relation of otolith microstructure to 

 metamorphic stages 



were developed in Stage-1 larval 

 otoliths, yet both were present in 

 all Stage-3 larval otoliths, it is prob- 

 able that they formed during Stage 

 2. Thus, the transition from clear 

 to opaque growth and initiation of 

 AP formation occur after the left eye 

 moves beyond the dorsal ridge and 

 metamorphosis (as defined in 

 Markle et al, 1992) begins, but be- 

 fore larvae are first collected on the 

 bottom. 



Formation of the first accessory 

 primordium in plaice and winter 

 flounder also does not occur until 

 the left eye has migrated at least 

 to the dorsal ridge of the cranium 

 (Alhossaini et al., 1989; Sogard, 

 1991). However, unlike Dover 

 sole, AP in otoliths of these spe- 

 cies can form before the eye has 

 moved past that point. Compari- 

 sons with other flatfish species 

 are more difficult. Accessory pri- 

 mordia form "at or shortly after metamorphosis" in 

 starry flounder (Campana, 1984a) and "after meta- 

 morphosis" in California halibut (Kramer, 1991); 

 however, the definition of metamorphosis relative 



Premetamorphic larvae Sagittal 

 otoliths of Stage-1 larvae between 

 20.6 and 51.5 mm were uniformly 

 translucent and lacked accessory 

 primordia. Since the left eye had 

 migrated to the middorsal ridge of 

 the cranium in each specimen, for- 

 mation of AP is not triggered by the 

 initiation of eye migration or move- 

 ment to this position in Dover sole. , 

 Cavities noted in Stage-1 larval 

 sagittae have not been described 

 previously and their derivation and 

 function are unknown. 



Metamorphic larvae Because 

 Stage-2 larval otoliths were not 

 available, the transition from clear 

 to opaque central areas and devel- 

 opment of the first two accessory 

 primordia cannot be attributed to 

 this stage with certainty. However, 

 because neither of these features 



Figure 16 



Right otolith of 100.4-mm Stage-5 juvenile Dover sole, Microstomus pacificus. caught 

 on 18 March 1991 I anterior to right), photographed with reflected light against black 

 background. Note the first annulus, which appears darker than the inner area. 

 Magnification = 50 x. A = annulus. 



