742 



Fishery Bulletin 91(4), 1993 



. • -' ' 



Figure 9 



Transverse section of right otolith of 47.5-mm Stage-3 Dover sole. Microstomas 

 pacificus, larva collected on 22 March 1989, showing recently-formed accessory pri- 

 mordium near medial surface (toward top) that would be undetectable in sagittal 

 section. Magnification = 400 x. 



tral primordium in at least one otolith of 78% of benthic 

 and 71.4% of pelagic Stage-3 larvae, 98.4% of benthic 

 and 100% of pelagic Stage-4 larvae, and 100% of Stage- 

 5 larvae, suggesting that most otoliths were enclosed 

 before or during Stage 3. Enclosure of growth from the 

 central primordium occurred an average of 33.7 days 

 after formation of the last accessory primordium (range 

 0-87, n=108). 



During Stages 3 and 4, SINT increases as the intes- 

 tinal loop extends into the secondary body cavity and 

 BD1A decreases as body depth shrinks (Markle et al., 

 1992). Consequently, fish with low SINT/BD1A ratios 

 are presumably at an earlier stage in the metamor- 

 phic process than fish with higher ratios. Benthic Stage- 

 3 larvae with at least one unenclosed otolith had a 

 lower ratio of SINT/BD1A (mean=1.06) than benthic 

 Stage-3 larvae with enclosed otoliths (mean=1.15) (t- 

 test, df=46, P=0.0096), as did pelagic Stage-3 larvae 

 (0.90 vs. 1.32, t-test, df=28, P=0.019), suggesting that 

 Stage-3 larvae with unenclosed otoliths were at an 

 earlier stage of development than Stage-3 larvae with 

 enclosed otoliths. 



Stage-3 larvae with enclosed otoliths were collected 

 an average of 24.4 days after enclosure (ranges 

 5.7-65.4, n=51) while Stage-4 larvae in the same col- 

 lections averaged 51.9 days (range=9.6-125.9, n=46). 

 The difference (27.5 days) may represent the average 

 duration of Stage 3. 



Otolith elongation along the anterior-posterior axis 

 became more pronounced following enclosure, as did 



asymmetry between left and right 

 otoliths. Left otoliths were heavier 

 (paired t-test, df=335, P<0.001), 

 longer (paired /-test, df=314, 

 P<0.001) and wider (paired /-test, 

 df=312, P<0.001) than right otoliths. 

 In addition, the proportion of otolith 

 length anterior to the central pri- 

 mordium was higher in right than 

 left otoliths (i-test, df=92, P<0.001) 

 by an average of 8.5% (Fig. 8, A- 

 D ). The number of accessory primor- 

 dia tended to be higher on right 

 than on left otoliths (paired /-test, 

 df=62, P=0.036), while more incre- 

 ments formed after the last AP 

 (paired t-test, df=34, P=0.006) and 

 after the point of enclosure (paired 

 t-test, df=15, P=0.011) on left than 

 on right otoliths. 



Stress checks became prominent 

 in sagittal section following enclo- 

 sure (Fig. 8, B-D). Enumeration 

 of stress checks and determination 

 of periodicity was difficult because 

 checks were often discontinuous 

 around the otolith and, even when continuous, the 

 number of observable increments between checks var- 

 ied regionally. However, mean periodicity of check 

 formation in 46 Stage-3 and Stage-4 otoliths collected 

 over a three-day period in March, 1990, suggested 

 synchrony of check formation in otoliths of different 

 fish and regularity in periodicity of check formation 

 (Fig. 13). Calculated dates of check formation did 

 not correspond to particular lunar phases. Number 

 of days between checks ranged from 5.7 to 33.6, with 

 a mode of 12.5 days and an average of 15.3 days 

 (Fig. 14). 



Other features of the enclosed peripheral zone in 

 older fish were the development of a rostrum (Figs. 1 

 and 15) and formation of translucent growth zones 

 (Fig. 16). All Stage-5 otoliths collected in January and 

 March had at least one translucent growth zone. This 

 first post-settlement translucent growth zone was ini- 

 tiated in late fall of the settlement year (240-293 days 

 after formation of the last AP) and was completed the 

 following spring (125 to 141 days later) in otoliths of 

 three Stage-5 juveniles. Based on daily increment 

 counts and seasonal deposition patterns, the first and 

 subsequent translucent growth zones are interpreted 

 as post-settlement annuli formed during slow winter 

 growth periods (Fig. 17, page 746). This interpretation 

 is consistent with Hagerman (1952) and Chilton and 

 Beamish (1982). 



Although there was little difference in weight be- 

 tween the largest Stage-4 and smallest Stage-5 Do- 



