NOTE Fey et al.: Effect of type of otolith and preparation technique on age estimation of Leiostomus xanthurus 549 



Method (source of increment counts) 



Sagittae 



tranverse section 

 one-side polished 



Sagittae 



tranverse section 

 two-sides polished 



Sagittae 

 whole 



• i -' r 



30 



28 



26 



24 



% 22 



E 



§ 20 



c 



o 54 



a> 



§ 52 



* 50 



48 

 46 

 44 

 42 

 40 



32 



(22) (22) (22) 



1 2 3 



B 



(21) (21) (21) 



(32) (32) (32) 



(13) (13) (13) 



12 3 12 3 



Increment counts within method 



Lapilli 

 whole 



(19) (19) (19) (17) (17) (17) (23) (23) (23) 



12 3 12 3 12 3 



(27) (27) (27) 



Figure 4 



Age of laboratory-reared spot [Leiostomus xanthurus) estimated from 

 daily otolith growth increments counted at three different occasions 

 for each preparation method: (A) larvae (34 d, 11.8 mm L T ); and (B) 

 juveniles (53 d, 24.3 mm L T ). Mean and 95% confidence interval 

 minimum, and maximum values are presented. Values in parentheses 

 indicate sample number. Dashed line indicates the real age. 



formed five days after hatching, which corresponds to 

 a time of exogenous feeding initiation in spot (Powell 

 and Gordy, 1980; Powell and Chester, 1985). The other 

 validation experiments on spot (Hettler, 1984; Siegfried 

 and Weinstein, 1989) provided no information on first 

 increment deposition time. In lapilli, increment depo- 

 sition occurred six days after hatching, but no other 

 studies are available for spot to compare and evaluate 

 these results. 



The inconsistency in the time of first increment for- 

 mation on the sagittae between the present study and 

 Peters et al.'s study 1 may be the result of underestima- 

 tion by the latter because they did not section or pol- 



ish the otoliths. Spot otoliths are relatively large and 

 thick and both sagittae and lapilli are difficult to read 

 without otolith preparation for fish older than 25-30 

 days (-7-9 mm TL). Peters et al. 1 found no increments 

 in sagittae of four- to five-day-old fish. Although in 

 the present study increments were not clear in sagit- 

 tae of four-day-old spot, fish collected from the same 

 tanks, 8 and 23 days later, had visible increments 

 since hatching. Even if it is difficult to explain why 

 the increments in sagittae of four-day-old-fish were not 

 visible, results presented in the present study support 

 the conclusion that first increment formation occurred 

 at hatching. 



