354 
Fishery Bulletin 95(2), 1997 
lowed by translucent band formation. The remain- 
ing eleven guitarfish were held in captivity for six 
months or less. Eight of the eleven were injected with 
Terramycin and did not show any growth beyond the 
Terramycin mark on the vertebrae and each had 
grown less than one centimeter in total length. Three 
control guitarfish (no injections) lived 10, 50, and 72 
days in captivity and showed no gain in length. 
Analysis of the outer edges of the centra with re- 
gard to periodicity of band formation provides fur- 
ther evidence for opaque band formation between 
October and December. Eight out of 17 guitarfish 
collected between October and November had opaque 
outer margins, whereas none of the 34 other guitar- 
fish collected during the other months (excluding 
August) had opaque outer margins. Three guitarfish 
caught in August showed opaque formation on the 
outer margins. A two-way test of independence indi- 
cated rejection of the null hypothesis that opaque 
band formation was independent of month (group 
l=January-June, group 2=August-November; 
G(adjusted)= 18.94, df=l, P=0. 00003). Therefore, it 
appears that opaque bands form from late summer 
(August) into fall (November). There was no pro- 
nounced relation between outer margin width and 
months of the year, probably indicating variation of 
growth within individual guitarfish. Another way to 
interpret these findings is to suggest that guitarfish 
lay down opaque bands bi-yearly (every other year). 
If this is the case, then the guitarfish were twice as 
old. However, the band formations found in the two 
captive guitarfish led us to assume that opaque bands 
were formed once per year. 
Assigning ages under the assumption of the an- 
nual formation of one opaque and one translucent 
band, we found that both males and females ranged 
in age from one to 11 years. Females ranged from 25 
to 130 cm TL. Males ranged from 23 to 114 cm TL. 
Percent agreement in band counts from three sepa- 
rate readings of two vertebrae from each guitarfish 
showed 73.8% in total agreement (43 guitarfish), 
16.4% disagreement ± 1 band (10 guitarfish), 6.5% 
disagreement ± 2 bands (4 guitarfish), and 3.3% dis- 
D= 0.415 cm 
D- 0.420 cm 
Figure 6 
Examples of opaque band formation indicating seasonal 
formation of bands (no photograph was available). The dia- 
grams of centra represent rays in the captive study that 
were injected twice with Terramycin. T x = first injection, 
T 2 = second injection, TZ = translucent zone, and D = cen- 
trum diameter. Gray areas indicate opaque band areas and 
are not to scale. Example A was held alive in captivity for 
13 months, and example B was alive for 14 months. 
