626 
Fishery Bulletin 96(3), 1 998 
parameters were comparable with earlier observa- 
tions by Stoskopf (1993) for captive G. cirratum. 
Discussion 
Tanaka (1990) determined that OTC injections at 
dosage levels from 20 to 80 mg/kg BW did not ad- 
versely affect growth or cause mortality in Japanese 
wobbegongs (O. japonicus) or swell sharks (C. 
umbratile). In agreement, the present study indicates 
no adverse effect of OTC treatment on the growth 
rate of injected G. cirratum. Therefore, continued use 
of OTC injection is still supported as an effective, 
nontoxic method for determining vertebral growth- 
band periodicity. In addition, OTC remains the su- 
perior chemical marker for elasmobranch age valida- 
tion in comparison with calcein, which appears highly 
toxic at similar dosage levels (Gelsleichter et al., 1997). 
Although OTC does not appear to affect short-term 
growth, high serum LDH and AST in OTC-injected 
G. cirratum may suggest that it can be hepatotoxic. 
High activities of LDH and AST are commonly used 
in the diagnosis of toxicant stress and hepatocellular 
injury, when these enzymes are leaked from damaged 
liver cells (Zimmerman etal., 1965; Racicot et al. , 1975; 
Krajnovic-Ozretic and Ozretic, 1987). Unfortunately, 
the diagnosis of toxicant stress in elasmobranchs with 
enzyme activity levels has not been well investigated. 
In addition, serial blood sampling of injected animals 
prior to and after injection is necessary for an appro- 
priate evaluation of serologic data. Consequently, in- 
terpretation of these data is speculative, yet may still 
indicate a harmful effect of OTC on elasmobranch physi- 
ology and thus require further investigation. 
Hepatic dysfunction is a common repercussion of 
OTC treatment in vertebrates. In several species, 
OTC administration causes acute hepatocellular in- 
jury that is often associated with intracellular fat 
deposition and cytoplasmic alterations (Weinstein, 
1970; Hennigar and Gross, 1977). However, these 
effects are usually associated with repeated exposure 
to dosage levels far greater than those used in fish 
Table 2 
Serologic parameters of nurse sharks at the end of the ex- 
perimental period after injection with oxytetracycline hy- 
drochloride (OTC) or vehicle at a dosage of 25 mg/kg body 
weight ; BUN = blood urea nitrogen; ALK P = alkaline 
phosphatase; LDH = lactate dehydrogenase; AST = aspar- 
tate aminotransferase; ALT = alanine aminotransferase. 
Values are means ± SE. The values marked with an aster- 
isk are significantly different from control at P < 0.05. 
Groups 
Control 
OTC 
Serologic parameter 
(n= 4) 
(n= 5) 
Glucose (mg/dL) 
16.2 ± 0.86 
18.0 ± 0.63 
Sodium (mM/L) 
272.7 ± 1.93 
275.4 ± 1.63 
Potassium (mM/L) 
5.45 + 0.10 
5.47 ± 0.08 
Chloride (mM/L) 
260.0 ± 2.71 
261.0 ± 1.48 
C0 2 (mM /L) 
7.7 ±0.25 
7.2 ± 0.20 
BUN (mg/dL) 
832.0 ± 12.17 
811. 6± 6.22 
Creatinine (mg/dL) 
0.10 + 0 
0.16 ± 0.02 
Uric acid (mg/dL) 
0.12 ± 0.03 
0.18 ±0.05 
Calcium (mg/dL) 
17.3 + 0.28 
17.8 ±0.24 
Phosphorus (mg/dL) 
4.12 ± 0.17 
4.14 ± 0.12 
Total bilirubin (mg/dL) 
0.1 + 0 
0.1 + 0 
ALK P (U/L) 
33.5 ±2.60 
54.6 ±9.79 
LDH (U/L) 
863.5 ± 122.9 
1810.8* ± 371.7 
AST (U/L) 
24.7 ± 3.77 
54.6* ± 9.35 
ALT (U/L) 
19.7 ± 1.25 
23.2 ± 1.71 
age validation studies (Lepper, 1951; Sborov and 
Sutherland, 1951). In addition, elasmobranch liver 
cells regularly contain large deposits of intracellu- 
lar fat in their normal state. Nevertheless, this stan- 
dard information may lend some credence to observa- 
tions on increased LDH and AST in treatment group 
specimens. Clearly, future studies on OTC toxicity 
should investigate other characteristics of health that 
are less conspicuous than animal growth or survival. 
In conclusion, the results of the present study in- 
dicate that OTC treatment does not produce short- 
term effects on G. cirratum growth that may compli- 
cate age validation. However, minor tangential evi- 
Table 3 
Differential white blood cell counts of nurse sharks at the end of the experimental period after injection with OTC or vehicle at a 
dosage of 25 mg/kg BW; % WBC is the proportion of all blood cells that are white. Values are means ± SE. 
Group or 
individual 
n 
Granulocytes 
(%) 
Lymphocytes 
(%) 
Monocytes 
(%) 
Thrombocytes 
(%) 
% WBC 
Control 
4 
21.4 ± 2.6 
51.1 ± 2.0 
1.4 ± 0.3 
26.1 ± 1.5 
12.0 ± 0.6 
OTC 
5 
22.4 ± 3.0 
50.3 ± 3.0 
1.9 ± 0.6 
25.4 ± 1.9 
11.2 ± 0.8 
