124 



Fishery Bulletin 101(1) 



Briiuard el al. 1 14X4) growth curve 

 Richards ( 1987) growth curve 

 Edwards ( 1985) growth curve 

 This study 



10 12 14 16 18 20 

 Age (years) 



24 26 28 30 .^2 



Figure 8 



Comparison of generalized von BertalanfTy growth cun'es for P. multidens from pre- 

 vious studies with that derived from this studv. 



available stock of P. multidens can be harvested on an an- 

 nual basis in a sustainable manner and that annual har- 

 vest rates should not e.xceed 107( of the average stock size. 



Discussion 



Sagittal otoliths were determined to be valid structures 

 for age determination in P. multidens. The edge-type clas- 

 sification system of three edge types used in this study is 

 capable of indicating whether the opaque zone has just 

 been formed or whether a new translucent zone is ready 

 to form. The use of marginal increment analysis (MIA) of 

 individuals of all ages exhibits a clear trend and demon- 

 strates conclusively that annual growth increments are 

 formed once per year Annual growth increments were 

 most conspicuous in the ventral lobe of the sagittal oto- 

 liths. However, we observed that experience is a critical 

 iactor in increasing the agreement and hence [precision 



of successive counts of annual growth increments in P. 

 multidens. 



The spring-summer peak in opaque zone formation ob- 

 served in our study is in accordance with the peak in opaque 

 zone formation identified by Fowler (1995) and Beckman 

 and Wilson ( 1995) for tropical fishes. The translucent zone 

 (the period of fast growth in the otoliths) is formed in the 

 summer months (January to May ) and the opaque zone ( the 

 slow growth period) is formed in the winter-spring months 

 (June to December). Translucent zones are relatively thin. 

 Declining sea-surface temperature (which was assumed to 

 reflect water temperature change at depth) was associated 

 with the onset of opaque zone formation in the otoliths of 

 P. multidens. Furthermore, reproduction is unlikely to play 

 a significant role in the timing of translucent zone forma- 

 tion in P. multidens because spawning occurs primarily in 

 the March -April period. These results indicate that water 

 temperature, doubtless in association with other factors, 

 provides a stimulus that Influences the endolymph fluid 



