431 
Energetics of larval red drum, 
Sciaenops ocellatus. 
Part II: Growth and 
biochemical indicators 
Ross I. Brightman 
Joseph J. Torres 
Joseph Donnelly 
Department of Marine Science 
University of South Florida 1 40 
Seventh Ave South, St. Petersburg, Florida 33701 
E-mail address. BrightmanOemail. spjc.cc.fi. us 
M. Elizabeth Clarke 
Division of Marine Biology and Fisheries 
Rosenstiel School of Marine and Atmospheric Science 
University of Miami 
4600 Rickenbacker Causeway, Miami, Florida 33 1 49 
Abstract .—The effects of ration level 
and temperature on growth were deter- 
mined for larval red drum, Sciaenops 
ocellatus, during its first two weeks of 
life. Larvae were raised in the labora- 
tory at 20°C at a ration level of 5.0 prey/ 
mL, at 25°C at ration levels of 0, 0.1, 
1.0, and 5.0 prey/mL, and in growout 
ponds at 25°C and 32°C and at ration 
levels of 4-6 prey/mL. Growth was mea- 
sured as standard length, wet mass, 
and dry mass. Proximate (water, ash, 
protein, and lipid) and elemental (C, N) 
composition was determined at larval 
ages of 0, 2, 4, 6, 10, and 14 d to pro- 
vide caloric values for the growing lar- 
vae and to examine the relative impor- 
tance of protein and lipid during tissue 
deposition in the very early life history 
of these larvae. Biochemical indicators 
of growth, RNA-DNA ratio, and activ- 
ity of the metabolic enzyme lactate de- 
hydrogenase (LDH) were examined in 
larvae reared at all temperature and 
ration combinations. The effectiveness 
of the biochemical indicators as prox- 
ies for growth was assessed by compar- 
ing the directly measured growth rates 
with RNA:DNA levels and LDH activ- 
ity. Larvae fed a ration of 1.0 prey/mL 
or less did not survive past the age of 
eight days. Growth rate increased with 
increasing temperature, reaching a 
maximum of 60% body mass/d in 
growout ponds at 32°C. Protein level 
(percent ash free dry mass: %AFDM) 
increased with increasing age in all 
treatments where individuals exhibited 
positive growth, whereas lipid (%AFDM) 
showed a concomitant decline. Nitrogen 
(%AFDM) and carbon (%AFDM) varied 
directly with protein and lipid contents, 
respectively. Biochemical indicators of 
growth showed a significant correlation 
with growth rate. However, the char- 
acter of the correlation changed with 
temperature. RNA-DNA ratios and en- 
zymic activities were lower at higher 
temperatures for equivalent growth 
rates. Introduction of a temperature 
term into multiple regression equations 
improved the relation between growth 
and the biochemical proxies. LDH ac- 
tivity scaled with the size of larvae, 
whereas RNA:DNA showed no signifi- 
cant relation with size. 
Manuscript accepted 4 February 1997. 
Fishery Bulletin 95:431-444 (1997). 
Red drum, Sciaenops ocellatus, is an 
important species in commercial 
and recreational fisheries in the 
southeastern United States, par- 
ticularly in the Gulf of Mexico. De- 
clines in red drum stocks (Swingle, 
1990) have stimulated considerable 
interest in the early life history of 
this species, resulting in stock en- 
hancement programs and larval 
monitoring programs designed both 
to improve and continually to assess 
the status of the fish in the field. 
Studies on red drum and other spe- 
cies indicate clearly that growth 
during the pretransformation pe- 
riod of development is particularly 
critical to survival (Buckley, 1980; 
Holt et al., 1981, a and b; Holt and 
Arnold, 1983; Holt, 1990). The in- 
crease in size and mobility that 
characterizes development during 
the early larval period results in an 
increase in the size range of prey 
items available to the larvae as for- 
age and a decrease in the size range 
of potential predators on the larvae. 
Two variables with great poten- 
tial to influence rates of growth are 
temperature and ration levels. As a 
subtropical species, red drum de- 
velop at temperatures greater than 
20°C, grow rapidly, and have a 
greater energy demand for metabolic 
processes than do larvae developing 
in colder systems. For example, red 
drum eggs at 25°C hatch in 24 h, and 
larvae begin feeding in 48-72 h, 
whereas cold water species, such as 
Atlantic cod, Gadus morhua, and 
winter flounder, Pleuronectes ameri- 
canus, developing at 4— 8°C, spend 30 
d as developing eggs. 1 High tempera- 
tures during early development 
stimulate rapid growth in red drum 
but leave them potentially more vul- 
nerable to rapid starvation in absence 
of sufficient food. The interaction be- 
tween temperature, ration level, and 
growth in size and calories, is an im- 
portant part of the energetics of lar- 
val red drum, basic information 
which is unavailable for red drum 
and limited for other subtropical te- 
leosts (Houde and Schekter, 1983). 
1 Hempel, G. 1979. Early life history of 
marine fishes; the egg stage. Univ. Wash- 
ington Press, Seattle, WA, 70 p. 
