Table 2 and are not supportive of a single stock 

 hypothesis. Dolphin in Barbados waters appear to 

 grow faster (Oxenford and Hunte 1983) than those 

 in North Carolina (Rose and Hassler 1968) and 

 Florida (Beardsley 1967). Note that scale annuli are 

 found in northern dolphin but not in southern 

 dolphin; a difference supportive of the assertion that 

 the two groups are distinct. Beardsley (1967) sug- 

 gested that the formation of the dolphin scale an- 

 nuli at Florida was correlated with the temperature 

 reduction occurring in the Florida Current during 

 winter. 



Dolphin from Barbados are larger but younger at 

 first sexual maturity than those from Florida. 

 Fecundity increases with fish size in both groups, but 

 Florida dolphin have higher fecundity at size than 

 Barbados dolphin (Oxenford and Hunte in press). 

 Mature eggs taken from Florida and North Carolina 

 dolphin are apparently larger than those from Bar- 

 bados dolphin. Intraspecific variation in egg size is 

 seldom environmental and is typically a function of 

 fish age (Bagenal 1971; Kazakov 1981). Mature egg 

 size does not increase with fish size/age for Barbados 

 dolphin (linear regression, r = 0.353 b = 0.0001). 

 Therefore, assuming that the differences observed 

 in egg size of southern and northern dolphin do not 

 result merely from differences in investigators' 

 methodologies, they are suggestive of separate 

 stocks as shown for different spawning groups of 

 herring (Blaxter and Hempel 1963; Cushing 1967) 

 and sockeye salmon (Foerster 1968; Bagenal 1971). 



Electrophoretic Comparisons 



In the electrophoretic survey, 55 presumptive loci 

 could be consistently scored. Of these, 39 were fixed 



for the same alleles in both samples, and a further 

 12 were close to fixation. Two isocitrate dehydro- 

 genase loci (Idh-2,3) and two esterase loci (Est-1,2) 

 had alternate alleles at a frequency >0.05, i.e. were 

 significantly polymorphic 



Seven phenotypes were observed at the Idh-2 locus 

 expressed in heart tissue (Fig. 5). The pattern of ac- 

 tivity at this locus is typical of an active dimeric en- 

 zyme with disomic inheritance (Darnall and Klotz 

 1972; Kirpichnikov 1981) and four alleles with 

 relative mobilities to 100, 123, 86, and 68. Thus, 

 putative genotypes could be assigned to the observed 

 phenotypes as indicated in Figure 5, and allelic fre- 

 quencies calculated (Table 3). Unequivocal assigna- 

 tion of genotypes to the phenotypes, observed at the 

 remaining polymorphic loci, was not possible in the 

 absence of inheritance data, since the loci have alleles 

 with overlapping mobilities. Idh-3 and Idh-2, ex- 

 pressed together in liver tissue, both have alleles with 

 relative mobilities to 100, 123, and 86, and although 

 the asymmetrically banded phenotypes could be 

 easily read, the presence of a null allele at Idh-3 

 meant that certain phenotypes could have been pro- 

 duced by a number of different genotypes. Est-1 and 

 Est-2 share all or some of four alleles, but the band- 

 ing intensity ratios of individual phenotypes could 

 not be determined. Hence, assignation of genotypes 

 to phenotypes at these loci was not possible In sum- 

 mary, only the Idh-2 locus, expressed indepen- 

 dently from Idh-3 in heart tissue, was considered 

 suitable for a comparison of Miami and Barbados 

 dolphin. 



The frequencies of alleles at Idh-2 differed signifi- 

 cantly in the two populations (chi-square 2x4 con- 

 tingency test: x 2 = 12.725, df = (r - 1) (C - 1) = 

 3, 0.01 > P > 0.0005; Table 3). Note that the varia- 



CO 



I— 



Q 

 O 



£ 123 _ 



o 



+ 



100 



86 



68 — ' 



PHENOTYPE 



ca 

 o 



123/123 100/100 86/86 123/100 100/86 123/86 100/68 

 (1) (1) (1) (1-2-1) (1-2-1) (1-2-1) (1-2-1) 



GENOTYPE 



BANDING 

 INTENSITIES 



Figure 5.— A starch-gel zymogram of the dimeric enzyme isocitric dehydrogenase, showing 

 the phenotypes observed and putative genotypes at the Idh-2 locus in heart extracts of the 

 dolphin, Coryphaena hippurus, from the western central Atlantic. Values in parentheses are 

 ratios of allele products. 



457 



