NOTE Benetti et al.: Growth rates of captive Coryphaena hippurus 



155 



for the first year of life (Oxenford and Hunte, 1983). 

 The AGR value reported in this study (0.227 cmd -1 ) 

 is well within this range and the 0. 1-0.6 cmd -1 range 

 reported by Brothers et al. (1983) for the Atlantic 

 bluefin tuna, Thunnus thynnus, another pelagic te- 

 leost. Only a few other pelagic teleosts exhibit growth 

 rates comparable to or higher than dolphin. These 

 include the Atlantic blue marlin, Makaira nigricans, 

 and the Atlantic sailfish, Istiophorus platypterus, two 

 of the largest North Atlantic pelagic teleosts. Prince 

 et al. (1991) estimated the AGR of young Atlantic 

 blue marlin from otolith microstructure as 1.66 cmd -1 , 

 a value nearly three times higher than that reported 

 for dolphin. From length frequencies of Atlantic sail- 

 fish, de Sylva (1957) estimated a maximum absolute 

 growth rate of 1.10 cmd -1 , twice as fast as that re- 

 ported for dolphin. Although the scope of these com- 

 parisons is limited owing to the different age classes 

 of fish, both the blue marlin and Atlantic sailfish 

 exhibit AGR's several times higher than those mea- 

 sured in this work. 



In this study, the feed conversion ratio (FCR) was 

 1.6 (dry feed/live fish). Similarly, Kraul and Ako 

 (1993) obtained a FCR of 1.6 with dolphin fed on a 

 commercially available pellet. FCR's of about 1.0 have 

 been reported for dolphin by Ostrowski et al. (1992), 

 Kraul (1989), and Kraul and Ako (1993), indicating 

 that they are efficient in converting the energy in- 

 take from feeds into growth. Relative to other spe- 

 cies, dolphin do not appear to require extraordinary 

 food intake to sustain their high growth rates, simi- 



lar to blue marlin (Prince et al., 1991). In this study, 

 cultured dolphin were fed 4% (dry feed) of their body 

 weight per day. This feeding rate is commonly used 

 for other fish species in captivity, which invariably ex- 

 hibit slower growth rates and higher FCR. Dolphin 

 appear to exhibit higher energetic efficiency than most 

 other teleosts because they use a proportionally larger 

 portion of the total gross energy ingested for growth 

 and metabolism than for excretion (Benetti, 1992). 



Although no spawning was observed, the slight 

 trend of decelerated growth after 180 days (Fig. 1) 

 could be due to the onset of maturation, which in 

 captive dolphin generally occurs in 6 months at 50— 

 55 cm and 2.0-2.5 kg (Kraul, 1991; Ostrowski et al., 

 1992), but has been observed to occur as early as 3- 

 4.5 months (Uchiyama et al., 1986). Somatic growth 

 rates in teleosts usually decrease after the onset of 

 maturation (Jones, 1976). For dolphin, however, the 

 linear equation fitted the data for the period studied 

 with the highest coefficient of correlation (r 2 =0.98). 

 A reason for this may have been the larger sample 

 size during the juvenile stage, when young fish grow 

 very fast. For instance, Hassler and Rainville (1975) 1 

 found that the length-age relationship of larvae and 

 early juvenile dolphin (13—83 days) was exponential. 



The VBGM's were used to model growth beyond 

 the scope of the data and therefore must be consid- 

 ered speculative. Although the data fitted both 

 VBGM's (length and weight) with a high coefficient 

 of determination (r 2 >0.98), the asymptotic sizes pre- 

 dicted by the models can not be tested because it has 

 not been possible to keep dolphin alive in captivity 

 for longer than 18 months. In this respect, the age 

 structure of the population should be considered. It 

 is possible that the potential longevity of the Hawai- 

 ian dolphin stock may not exceed this maximum age 

 in captivity (about 18 months). For instance, the lon- 

 gevity of dolphin from Florida was estimated to be 4 

 years, but only 2% of the population was found to be 

 older than 2 years (Beardsley, 1967), and only 4% in 

 North Carolina (Rose and Hassler, 1968). The maxi- 

 mum life span of the Southern Caribbean dolphin 

 stock does not appear to exceed 18 months, and few 

 individuals of the North Caribbean stock live longer 

 than 2 years (Oxenford and Hunte, 1986). 



The asymptotic length estimated by the VBGM 

 (1,^=1.69 m) compares well with existing data for wild 

 fish in the literature (L m =1.89 and 1.53 m for males 

 and females, respectively) (Beardsley, 1967). The es- 

 timated asymptotic weight (^=58. 4 kg), however, 

 is much higher than the maximum weight of 46 kg 

 reported for this species (Florida Sportsman, 1979). 



1 Hassler, N. W., and R. P. Rainville. 1975. Techniques for hatch- 

 ing and rearing dolphin, Coryphaena hippurus, through larvae 

 and juvenile stages. Sea Grant Publ. UNC-SG-75-31, 17 p. 



