348 



Fishery Bulletin 98(2) 



significant. For the comparison by sex, however, the 

 test approached significance, with P=0.138. Given 

 the variabiHty in data, the power of this test was 

 probably low. Furthermore, growth was clearly non- 

 linear and decreased over time. To reach a size of 600 

 mm FL in 100 days, cumulative growth would have 

 to be 6 mm FIVday. The maximum observed cumu- 

 lative growth rate was 9.5 mm FL/day for a fish of 

 1303 mm FL and 137 increments. On average, fish 

 of 110-150 days grew 3.3 mm FL/day, those 170-220 

 days old grew 2.9 mm FL/day and those 230-270 

 days of age grew 2.1 mm FL/day. Parameter values 



1400 n 



1200 



E 



.c 



"& 



c 



0) 



1000 



800 



600 



400 



150 250 



Growth Increments 



Figure 2 



Relation between fork length and number of sagittal rings 

 fish from Puerto Rico. Straight line indicates linear growth 

 Curved line indicates growth according to the von Bertal 

 ( see text ). 



350 



for dolphin- 

 over all fish, 

 anffv model 



for the von Bertalanffy model (Fig. 2) are shown in 

 Table 2. It was not possible to fit the model to the 

 data sorted by both coast and sex, owing to reduced 

 sample size in relation to large amount of variance. 

 Differences between sexes were the greatest, and 

 the confidence limits on k indicated statistical sig- 

 nificance would occur at a P-value of approximately 

 0.06. Extrapolation of the von Bertalanffy equation 

 for all individuals predicted a cumulative growth 

 rate of 3.59 mm FL/day over the first year. 



Discussion 



All linear growth rates for dolphinfish (Table 1) were 

 greater than those reported by Beardsley ( 1967 ) and 

 Rose and Hassler (1968) (Table 3). However, use of 

 linear growth estimates is justified largely by the 

 high variability observed in fork lengths for a given 

 age; high variability masks any underlying growth 

 pattern, thus making a linear model the simplest 

 and most parsimonious, but not necessarily the most 

 realistic model. A better approach is to use a biologi- 

 cally realistic model, in this case the von Bertalanffy 

 model. The resulting parameters of the von Berta- 

 lanffy model for the Puerto Rico data are consistent 

 with the known biology of dolphinfish. Asymptotic 

 lengths were in accord with known maximum lengths, 

 values of ^Q were very close to zero, even though they 

 represented extrapolations of three months (=25% of 

 maximum age observed), and growth coef- 

 ficients were high. Growth rates predicted 

 for dolphinfish from these equations give 

 a different picture from those provided by 

 the linear model. For all fish, growth aver- 

 aged over 1 year was 3.59 mm FL/day (3.31 

 mm SL/day ); growth averaged over the first 

 6 months was 5.57 mm FL/day (5.13 mm 

 SL/day). These rates are comparable to the 

 higher values reported in Table 3. 



Growth rates for dolphinfish reported 

 from previous studies (Table 3) are of ques- 

 tionable value when they lack uniformity 

 in length units and in the time over which 

 growth is evaluated, when growth is not 

 portrayed accurately, and when the size for 

 which growth is reported is unclear. The 

 use of the von Bertalanffy growth function 

 allows standardization for comparison of 

 growth. Parameters for the von Bertalanffy 

 model were calculated for four previous 

 studies in which length-at-age data were 

 reported (Table 4). Comparisons using <P' 

 (^log/C + 21ogL^^), the growth performance 

 index of Pauly and Munro (1984), suggests 



