Massutf et al : Otolith microstructure, age, and growth of Coryphaena hippurus 



895 



otoliths. Growth parameters for the whole popula- 

 tion and by sex are shown in Table 2. 



Length-frequency distributions for the 1990 and 

 1991 fishing seasons, based upon sampling of a fish- 

 ery on juveniles, are given in Figure 5. Fish caught 

 in this fishery from August to December measured 

 18-70 cm FL. The monthly length distribution indi- 

 cated a rapid increase in the mode, mean, and mini- 

 mum and maximum sizes for the catch. Von 

 Bertalanffy growth parameters for this fraction of 

 the population were estimated for the 1990 and 1991 

 fishing seasons (Table 2). 



Discussion 



The length-weight relationships obtained, showing 

 negative allometric growth in females and isometry 

 in males, are in accordance with the sexual dimor- 

 phism of C. hippurus. In this species there is a char- 

 acteristic bullhead in males which, in the western 

 Mediterranean, begins its development in individu- 

 als around 50 cm FL (Massuti and Morales-Nin, 1997). 

 Similar results are obtained in other areas (Palko et 

 al., 1982; Chatterji and Ansari, 1985), with a negative 

 allometry that is stronger in females than in males. 



Our study confirmed the daily nature of otolith 

 growth increments in the first month of life for C. 

 hippurus as reared fish. The strong correlation of 

 mean sagittal counts to known fish age validated the 

 use of otolith growth increments in the aging of ju- 

 veniles up to 40 days old. Because regular incremen- 

 tal formation began on day one, no adjustment was 

 required to estimate age from incremental counts of 

 sagittae from wild fish. 



Results suggest that the age of adult specimens is 

 underestimated by the otolith method. This is clear 

 when age-length relationships from daily growth 

 rings in otoliths and from annuli in scales are plot- 

 ted. For the same size interval, the otolith reading 

 gave ages between and 1 year, whereas interpreta- 

 tion of annuli in scales of adult fish gave ages to 3 years. 

 This might be due to methodological problems in otolith 

 preparation and interpretation. Consequently, the use 

 of scales seems to be the best aging method for adult 

 fish fi-om the Mediterranean, ft-om the point of view 

 both of preparation and of results obtained. 



The interpretation of juvenile fish age from daily 

 growth increments seemed accurate, with a low per- 

 centage of disagreement between readers. To test the 

 precision of this method, juvenile birthdate distri- 

 bution was calculated by subtracting age in days from 

 the date of capture. This showed a long period with 

 peaks in the second fortnight of June 1990 and the 

 first fortnight of July 1991 (Fig. 6). This small varia- 



Figure 3 



Light micrographs of Coryphaena hippurus sagittal 

 otoliths. (A) Daily growth increments in the core region of 

 the otolith (scale bar=15 ^mi; iBl narrow increments in 

 the central region of the otolith, showing rhythmic growth 

 "patterns of 7-, 14-, and 28- increment groupings (scale 

 bar=25;/m): (C) wider increments in the area of the otolith 

 edge (scale bar=30 ^m). 



tion between years might be due to changes in the 

 spawning peak or to differential mortality (Campana 



