(174-1,100 mm SL) at 100X. 



There is a close correlation between the number of 

 sagittal rings and fish standard length (mm SL) = 

 58.608 + 4.709iV; r= 0.95; Fig. 3). Assuming that the 

 rings are daily, the average growth rate for all fish is 



All lish 



400 



58 61 



FIGURE 3.— The relationship of dolphin standard length to number 

 of sagittal rings. The upper line (adults) represents the upper set of 

 scatter points only. 



4.71 mm/d: the average growth rate for adults (size 

 range 700-1,100 mm SL) is 1.43 mm/d (mm SL) = 

 7 11.574 + 1.425 N;r= 0.57; Fig. 3). Using changes in 

 mean length of a cohort (Fig. 4), the average growth 

 rate for dolphin of size range 600-1,200 mm SL is 

 1.53 mm/d. 



The close correlation between number of sagittal 

 rings and fish standard length suggests that ring for- 

 mation is periodic. The similarity in growth rates 

 obtained for the same population, using length- 

 frequency distributions and the otolith rings, sug- 

 gests that periodicity of the ring formation is daily. 



Data published on growth rates of dolphin vary con- 

 siderably (Table 1). These differences may reflect 

 use of fish of different ages (the present study sug- 

 gests that adults grow slower than juveniles), or may 

 result from differences in aging techniques, in water 

 temperatures, or in health and degree of provisioning 

 of captive specimens. 



We conclude by suggesting that daily rings occur in 

 the otoliths of all sizes of dolphin fish (174- 1,100 mm 

 SL) and, therefore, that counts of otolith rings pro- 

 vide an alternative method of estimating age in this 

 species. Moreover, since there is a linear correlation 



January 



600 



700 



800 900 



Standard length (mm) 



1000 



1100 



1200 



FIGURE 4. — Monthly length-frequency distributions of adult dolphin landed in Barbados between January and June. 



908 



