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Fishery Bulletin 95(2), 1997 
ment to that found by Cailliet et al. (1983) in the 
blue shark, Prionace glauca, and Casey et al. (1985) 
in the sandbar shark, Carcharhinus plumbeus. Di- 
ameters of vertebral centra were measured with an 
ocular micrometer at 12x magnification. Each verte- 
bra was read three times, one month apart, and those 
vertebrae in which all three readings agreed were 
used in the final analysis. To determine periodicity 
of band formation, the condition of the outermost 
band was recorded as either translucent, opaque, or 
undetermined. Ages were assigned to guitarfish on 
the basis of the number of opaque bands. 
Statistical analyses included least squares regres- 
sion analysis to provide predictive equations for es- 
timates of TL from centrum diameter, TL from band 
counts, TL from second dorsal fin length (2D), and 
age from TL. Regression parameters were obtained 
with SAS PC software (SAS, 1985). Male and female 
growth curves were constructed from von Bertalanffy’s 
growth curve equation (von Bertalanffy, 1938): 
L t = (l-e - * u “ (o> ), 
where L t = total length at time t\ 
= maximum theoretical length of species; 
k = growth constant; 
t 0 = theoretical age at zero length; and 
t = estimated age. 
The von Bertalanffy growth equation was fitted by 
using FISHPARM (FISHPARM software [Prager et 
al., 1989]) to estimate the growth constant k and was 
compared to a linear least squares regression by us- 
ing the same data. 
Growth rate of guitarfish in captivity 
The main purpose of the captivity study was to de- 
termine if Terramycin (manufactured by Pfizer Ag- 
ricultural Division) produced a readable time mark 
in vertebral centra of guitarfish. The study was de- 
signed to maintain guitarfish in captivity for at least 
one year to determine the temporal periodicity of band 
formation and growth rate of guitarfish in captivity. 
Over a two-year period, 13 guitarfish (five males 
and eight females) were taken live and placed in an 
outdoor saltwater tank at California State Univer- 
sity, Long Beach, California. Before guitarfish were 
introduced into the tank, we repeatedly measured 
TL, DW, ID, and 2D until we obtained consistent, 
repeatable measurements. Guitarfish were first 
weighed, and then injected with Terramycin (dos- 
age=0.5 mg/kg). Terramycin was injected with tuber- 
culin-type syringes in the epaxial musculature, 
within two centimeters of the skin surface. Guitar- 
fish were fed every other day a diet of anchovy, mack- 
erel, mud shrimp, ghost shrimp, and squid. 
When a guitarfish died in captivity, it was used for 
vertebral and reproductive analysis. Vertebral 
growth (beyond the time mark) was measured with 
the aid of a Wilde dissecting scope and ultraviolet 
flashlight (Fig. 4). Because time marks could be seen 
only under ultraviolet light and the opaque band for- 
mation could not be seen under ultraviolet light, 
transmitted light was used immediately after the 
ultraviolet light to compare the time mark with the 
opaque band position. This method allowed deter- 
mination of whether a translucent or opaque band 
had formed after the time mark. 
Reproductive maturity 
Thirty-six female guitarfish were dissected for ex- 
amination of their reproductive tract. Mature indi- 
viduals were categorized into one of three visual 
stages: Stage 1 — shell gland not differentiated from 
uteri, uteri empty, small follicles present; Stage 2 — 
shell gland and characteristic diagonal white band 
pattern within it forming, large Graafian follicles 
present, uteri thick; and Stage 3 — uteri full, large 
Graafian follicles present. Immature individuals had 
no visible egg follicles, uteri were thin and transpar- 
ent, and shell glands consisted only of a slight bulge 
in the upper portion of the uteri. These stages were 
distinct; any female guitarfish, upon dissection, could 
be categorized by using these criteria. No dissections 
were made for male guitarfish. The maturity of male 
guitarfish was determined by measuring the clasper 
width and length and by comparing the clasper length 
to total length, as well as by visual examination. 
Results 
Age and growth 
Growth of the vertebrae was proportional to the 
growth of the guitarfish, as evidenced by the signifi- 
cant positive relation between centrum diameter and 
total length for females and males (females: r 2 =0.98, 
n- 27, P=0.0001; males: r 2 =0.96, n=31, P=0.0001; Fig. 
5). The number of bands per vertebra correlated 
strongly (r=0.92, n= 42, P=0.0001) with the diameter 
of the centra, indicating that individuals having more 
bands had larger centra. Similarly, the number of 
opaque bands present in any individual was higher 
in larger guitarfish; the regressions were significant 
for females and males (females: r 2 =0.95, rc = 19, 
P=0.0001; males: r 2 =0.78, n=24,P=0.0001). APearson 
correlation matrix analysis of total length, centrum 
