624 
Evaluation of toxicity of 
oxytetracycline on growth of 
captive nurse sharks, 
Ginglymostoma cirratum * * 
James Gelsleichter 
Virginia Institute of Marine Science 
School of Marine Science, College of William and Mary 
Gloucester Point, Virginia 23062 
E-mail address, jimg@vims.edu 
Enric Cortes 
Charles A. Manire 
Robert E. Hueter 
Mote Marine Laboratory, Center for Shark Research 
1 600 Ken Thompson Parkway 
Sarasota, Florida 34236 
John A. Musick 
Virginia Institute of Marine Science 
School of Marine Science, College of William and Mary 
Gloucester Point, Virginia 23062 
Validation of age estimates derived 
from calcified structures is an es- 
sential component of all fish age 
and growth studies (Beamish and 
McFarlane, 1983). In elasmobranchs, 
age validation is accomplished 
through injection of tetracycline 
antibiotics, particularly oxytetracy- 
cline hydrochloride [OTC] (Cailliet, 
1990). At a standard dosage level 
of 25 mg/kg body weight ( B W ), OTC 
is deposited at sites of active calci- 
fication and produces vivid, endur- 
ing marks in dorsal-fin spines and 
vertebral centra (Holden and Vince, 
1973; Smith, 1984; Beamish and 
McFarlane, 1985; Branstetter, 
1987; Brown and Gruber, 1988; 
Natanson and Cailliet, 1990; Rusher 
et al., 1992; Natanson, 1993; Walker 
et al. 1 ). The location of these fluo- 
rescent marks can then be exam- 
ined to determine if the structure 
in question accurately reflects age. 
Such OTC treatment is generally 
considered benign, yet few scien- 
tists have directly examined the 
potential toxicity of this compound 
to elasmobranchs. However, if OTC 
injection alters the growth or 
health of treated elasmobranchs, 
its value as a chemical marker for 
age validation may be severely com- 
promised. Thus, studies on the tox- 
icity of OTC and other potential 
chemical markers (Gelsleichter et 
al., 1997) are essential for the im- 
provement of elasmobranch ageing 
biotechnology. 
Chemical toxicity associated with 
OTC treatment has been well docu- 
mented in several teleost ageing 
studies. For example, injection of, 
or immersion in, OTC at recom- 
mended dosage levels (Beamish 
and McFarlane, 1983) has been re- 
ported to produce lethargy, behav- 
ioral abnormalities, and mortality 
in treated specimens (Schmitt, 
1984; Wilson et al., 1987; Marking 
et al., 1988; Monaghan, 1993; Bum- 
guardner and King, 1996). In con- 
trast, Tanaka (1990) reported that 
various dosage levels of OTC (20— 
80 mg/kg BW) did not significantly 
affect growth rates of injected Japa- 
nese wobbegongs ( Orectolobus japon- 
icus) or swell sharks (Cephaloscyl- 
lium umbratile). Unfortunately, no 
other studies have investigated the 
possible implications of OTC treat- 
ment in elasmobranchs and, thus, 
they remain largely unclear. 
The goal of the present study was 
to evaluate the effect of OTC treat- 
ment on the growth rate of captive 
nurse sharks, Ginglymostoma cirra- 
tum. The potential effect of OTC in- 
jection on nurse shark health is also 
discussed on the basis of serologic 
and hematologic observations. 
Materials and methods 
Nine age-0 and age-1 G. cirratum 
were collected in the Florida Keys 
and transported to the laboratory, 
where they were maintained in out- 
door circular tanks (capacity rang- 
ing from 3,200 to 12,000 L). The 
experimental tanks can operate as 
either open or recirculating sys- 
tems and were subjected to natu- 
ral photoperiod and temperature 
1 Walker, T. I., R. A. Officer, J. G. Clement, 
and L. R Brown. 1995. Southern age 
validation: Part I — Project overview, ver- 
tebral structure and formation of growth 
increment bands used for age determina- 
tion. Final Report to the Fisheries Re- 
search and Development Corporation, 
FRDC Project 91/037. Department of 
Conservation and Natural Resrouces, 
Queenscliff, Victoria, Australia. 
* Contribution 2093 of the Virginia Insti- 
tute of Marine Science, School of Marine 
Science, College of William and Mary, 
Gloucester Point, Virginia 23062. 
Manuscript accepted 10 November 1997. 
Fishery Bulletin 96:624-627 (1998). 
