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Fishery Bulletin 95(3), 1997 
Objectives of the present study were four-fold. The 
first was to examine growth in size and energy in 
laboratory-reared red drum larvae, from egg to on- 
set of transformation, at a single ration level (5 prey/ 
mL) and at two temperatures (20 and 25°C). This 
examination was achieved by using direct measure- 
ments of standard length and mass with age; the 
biochemical composition and caloric value of the 
growing larvae were described by analyzing their 
proximate and elemental composition (water, ash, 
protein, lipid, carbon, and nitrogen). The second was 
to examine the relation of growth in size and energy 
as a function of ration level (0, 0.1, 1.0, and 5.0 prey/ 
mL) at a single temperature (25°C). The third was to 
compare growth in size and energy in laboratory- 
reared larvae at 20 and 25°C and in the more het- 
erogeneous conditions encountered by pond-reared 
larvae at 25 and 32°C. The fourth objective was to 
describe the relation between growth, temperature, 
and biochemical indicators of growth and condition: 
RNArDNA ratios and activity of the key intermedi- 
ate metabolic enzyme lactate dehydrogenase (LDH). 
Methods and materials 
Laboratory maintenance 
Fertilized eggs were obtained from the Florida De- 
partment of Environmental Protection (FDEP) hatch- 
ery, Port Manatee, Florida. Broodstock were main- 
tained at 25°C and 30 ppt. Eggs were obtained from 
five females and from separate spawnings, from No- 
vember 1990 to November 1991, for all growth ex- 
periments described below. Broodstock females were 
similar in size, kept in highly controlled conditions, 
and fed well. Spawning was induced naturally by 
manipulation of photoperiod. As a consequence, eggs 
were very uniform in size, 0.9 to 1.0 mm in diameter. 
Eggs were transported to the USF Marine Science 
Laboratory in St. Petersburg and sorted into 26-L ex- 
perimental aquaria at a concentration of 2,500-3,000 
individuals per aquarium. High mortality associated 
with first feeding resulted in a 30-40% reduction in 
initial numbers by day 3. Aquaria were placed in a 
photoperiod- and temperature-controlled incubator and 
maintained at either 20°C or 25°C and at a salinity of 
30 ppt. Eggs were introduced to the 20°C temperature 
by slow exchange of water over a 60-minute period. A 
13-h light and 11-h dark photoperiod was used through- 
out all experiments. Larvae were fed rotifers (Brach- 
ionus plicatilis) beginning at day 3 posthatch until flex- 
ion (approximately day 14), when experiments were 
terminated. Aquaria were aerated and a portion of the 
saltwater in each was changed daily. 
Rotifers were obtained from Florida Aqua Farms, 
Dade City, Florida, and cultured according to the 
procedure of Hoff and Snell (1987). Rotifers were fed 
Chlorella once a day to avoid any loss in nutritional 
value. Seawater for culturing was obtained off- 
shore in the Gulf of Mexico. The seawater was coarse- 
filtered, then treated with bleach (sodium hypo- 
chorite, 5.25%) to remove any additional plankton, 
and neutralized with sodium thiosulphate. Seawa- 
ter salinity was adjusted with distilled water and 
Tropic Marine Seasalt to achieve a final salinity of 
30 ppt. 
Pond maintenance 
Pond-reared red drum larvae were obtained from the 
FDEP growout ponds, Port Manatee, Florida. Lar- 
vae from a single spawn were added to the plank- 
ton-rich ponds within 24 hours after hatching and 
allowed to grow. Two ponds, one at 25°C and another 
at 32°C, were sampled for the first 18 days of life of 
the red drum larvae. Temperature was monitored 
twice daily; the average temperature for the two- 
week sampling period was used to characterize the 
ponds. 
Prey items in the ponds were monitored by siev- 
ing water samples into two size categories: 35-220 
pm (copepod nauplii, rotifers, and small copepods) 
and larger than 220 pm (copepods); prey were then 
counted in 200-mL aliquots of each size range. The 
concentration of prey between 35 and 220 pm was 
3-5 prey/mL, whereas that greater than 220 pm was 
0.5-1 prey/mL in both the 25°C and 32°C ponds. 
Growth versus prey density 
Eggs from a single spawn were divided into four 26-L 
aquaria for experiments on growth versus prey den- 
sity at 25°C. Prey were provided at four densities, 0, 
0.1, 1.0, and 5.0 prey items per mL, from first feed- 
ing (day 3) through the start of flexion (day 14). Prey 
concentrations were monitored twice daily by remov- 
ing a 25-mL sample from each aquarium, counting 
the number of prey in 5-mL aliquots, and taking the 
average. Prey concentrations were adjusted as nec- 
essary. Larvae reared at 20°C were fed prey at a ra- 
tion level of 5.0 prey items per mL. 
Standard length measurements Growth in stan- 
dard length was monitored according to prey con- 
centration. Aquaria with 0, 0. 1, and 1.0 prey/mL were 
sampled daily. Aquaria with 5.0 prey/mL were 
sampled every other day, and ponds were sampled 
every third day. The samples were taken each morn- 
ing before the larvae began to feed. Standard length 
