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Fishery Bulletin 94(1), 1996 



10 12 14 16 18 20 22 24 

 Otolith radius to extrusion check (pm) 



Figure 2 



Frequency distribution of the otolith radius, mea- 

 sured to the extrusion check, among aged planktonic 

 larvae, Sebastes jordani. 



A sample of 85 gestating prolarvae were staged 

 from mature female specimens and the total radius 

 of the otolith measured. Results show that prolarval 

 otoliths grow in size as embryonic development pro- 

 ceeds (Fig. 3), and that by attainment of stage 6 the 

 average total otolith radius was 16.91 /jm ( rj = 1.01 

 ,uml. A pooled variance MestlSnedecor and Cochran, 

 1967), comparing the mean otolith radius at the ex- 

 trusion check (R Q ) of planktonic larvae with the mean 

 total otolith radius of stage 6 gestating prolarvae, 

 was not significant (f =-0.136; df=2,241;P>0.50). This 

 test was powerful, with a difference in the means as 

 small as 0.43 ^m being significant at a = 0.05. More- 

 over, an extrusion check was not observed in any 

 otoliths from gestating larvae. These results indicate 

 that the check mark forms at parturition. 



Observations of gestating and planktonic S. 

 jordani otoliths with the SEM revealed a well-de- 

 fined microstructure (Fig. 4). The central area com- 

 prised a primordial region which often displayed a 

 cluster of etchant-resistant, crystal-like particles 

 (Fig. 4, B and C). Surrounding the particles was a 

 more deeply etched zone presumed to be predomi- 

 nated by matrix material. Distal to this was a calci- 

 fied region which generally displayed up to three 

 weakly expressed concentric zones. Incremental 

 growth was considered to be very ambiguous here; 

 the core area included this calcified region around 

 the primordium and was defined by a distinct deeply 

 etched zone (Fig. 4, B, C, and D). Distal to the core 

 boundary, regular incremental growth was observ- 

 able in most of the preparations. Increments in this 

 preextrusion growth phase were typically 0.3-0.6 /mi 

 wide but were of low topographical and compositional 



contrast in the BEI images (Fig. 4, B and C). There 

 were moderately consistent patterns of broader light 

 and dark areas within the region of preextrusion 

 otolith deposition. 



The defining boundary for the preextrusion otolith 

 is a deeply etched zone which corresponds to the ex- 

 trusion check noted in light microscope observations 

 (Fig. 4, A, C, and D). Distal to this landmark, incre- 

 mental growth consisted of a regular depositional 

 pattern with distinct zonation and gradually increas- 

 ing spacing ( Fig. 4, C-F ). There was individual varia- 

 tion in the spacing pattern of the first 5-10 incre- 

 ments. Some larvae had closely packed increments 

 (Fig. 4F), whereas at the other extreme, some larvae 

 exhibited obviously faster otolith growth immediately 

 after extrusion (Fig. 4E). 



A comparison of increment widths derived from 

 optical microscopy with those derived from SEM ob- 

 servations shows that otolith microstructure was 

 adequately resolved with the optical system (Fig. 5). 

 Importantly, the SEM did not detect the existence of 

 increments too small to resolve with optical micros- 

 copy. Increment widths typically increase in size 

 during the earliest stages of larval growth (e.g. 

 Campana et al., 1987) and this increase was observed 

 in S. jordani. The width of the first postparturition 

 increment was approximately 0.6-1.0 pm, which can 

 be resolved by optical methods. Subsequent incre- 

 ments, at least up to day five, slowly increased in 

 size. 



A growth model for the first month of life was de- 

 rived from the age and length data. Length was first 

 log-transformed because NL variance was propor- 



