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



893 



Table 1 



Length-weight relationship parameters estimated by ex- 

 ponential regression equations (,v = ax^\ between fork 

 length (cm) and total weight (g) in Coiyphaena hippurus. 

 n - number of specimens; SE = standard error of slope; r 

 = correlation coefficient. 



Population n 



SE 



Females 



Males 



Total 



192 

 154 

 350 



0.0139 

 0.0092 

 0.0113 



2.8983 

 3.0187 

 2.9605 



0.0011 0.997 

 0.0018 0.996 

 0.0007 0.996 



The sagittae of C hippurus are small in rela- 

 tion to fish size and generally butterfly-shaped, 

 although they display different structural patterns 

 with ontogenic development. The larval otoliths 

 are round and the development of the rostrum 

 starts at 8 days (Fig. 1, A and B). The sulcal struc- 

 ture is formed in 12-day-old larvae (Fig. lO; the 

 rostrum and antirostrum were, on average, sepa- 

 rated in 17-day-old larvae (Fig. ID). 



Otoliths prepared for SEM observation showed 

 differences depending on the etching agent. The 

 otoliths etched with EDTA had less clear growth 

 increments than did otoliths etched with HCl. 

 These differences might be due to high protein 

 content in the otoliths, which collapsed when the 

 aragonite crystals were completely removed with 

 EDTA. Whole otoliths showed the presence of 

 concentric laminations or ridges (Fig. 2A) which 

 revealed that the core region grew by the deposi- 

 tion of successive layers on the inner side. Sec- 

 tions of otoliths showed the typical pattern of in- 

 cremental and discontinuous units, which formed 

 growth increments with variable widths depend- 

 ing on the otolith area (Fig. 2, B and C). Some 

 rhythmic patterns were also evident with 7-14 

 increment groupings (Fig. 2, B and D). 



Under the light microscope, otoliths revealed a 

 pattern of alternating light and dark concentric 

 rings surrounding a core, which was deposited at 

 the earliest stages of development (Fig. 3A). The 

 width of the increments varied from the core to the 

 edge, with narrow increments near the center of the 

 otolith and at the edge, whereas wider ones were 

 laid down from the first to the third month of life 

 (Fig. 3, B and C). These differences in increment 

 width may reflect periods of differential gi'owth. 

 Larger increment patterns, or bands composed of 

 groups of 7-14—28 increments, were also observed 

 (Fig. 3B), suggesting lunar growth rhythms. 



From 93 reared lar\'ae of known age, a total of 75 

 otoliths (81%) could be read under the light micro- 



Figure 1 



Photomicrographs of sagittal otoliths from Coryphaena 

 hippurus larvae reared in captivity: lA) 6-day-old larvae of 

 6.1 mm SL (scale bar=25 ^m); (Bl 8-day-old larvae of 8.5 mm 

 SL (scale bar=29 /jm); (C) 12-day-old larvae of 8.8 mm SL 

 (scale bar=34 ;/mi: (Dl 17-day-old larvae of 30 mm SL (scale 

 bar=56 /jml. (E) Poorly defined increments laid down around 

 the core (scale bar=90 ^m). 



scope. These larvae measured 3.8-65.0 mm SL, and 

 their otolith radii ranged from 10.7 mm (at day 0, 



