Brightman et al.: Energetics of larval Sciaenops ocellatus 
441 
Table 3 
Multiple regressions describing instantaneous protein-specific growth (Y; %/d) in red drum larvae versus temperature (T), ration 
(0/ml, 5/mL, and pond), RNA:DNA, and LDH activity (units/gWM). Only significant regressions are presented (P< 0.05). 
Equation 
% 
Y 
n 
r 2 
P 
1 
T 
Y= 2.7 IX,- 49.52 
20 
0.21 
0.023 
2 
Ration 
Y = 6.35X i - 8.53 
20 
0.45 
0.001 
3 
T 
Ration 
Y=2.07X i + 5.67X,,- 58.34 
20 
0.57 
0.022 
4 
RNA:DNA 
Y = 14.76X - 3.64 
17 
0.30 
0.013 
5 
T 
RNA:DNA 
Y = 2.59X ; + 14.61X,, - 69.41 
17 
0.56 
0.007 
6 
LDH 
Y = 1.39^-8.17 
13 
0.34 
0.022 
7 
T 
LDH 
Y=2.55X ; + 1.26X„ - 70.35 
13 
0.57 
0.034 
Discussion 
Growth versus prey density 
Standard length and mass measurements The 
basic pattern of growth and development in red drum 
larvae, e.g. in size at flexion, was similar for larvae 
under a wide variety of rearing conditions. Within 
the basic blueprint, growth and development of red 
drum larvae fed to satiation could be accelerated or 
retarded according to the rearing temperature. 
Thus, larvae raised in the laboratory and the ponds 
underwent metamorphosis at roughly the same size, 
independent of the age of the larvae. In the case of 
the 32°C pond, day-7 larvae were already the size of 
day- 14 larvae reared at 25°C in the laboratory, and 
were at the same stage of development. Similarly, 
dry mass at transformation was approximately the 
same in the laboratory and ponds, despite the differ- 
ences in chronological age. 
Proximate and elemental composition of larvae 
Red drum larvae, whether fed to satiation or starved, 
depleted their lipid level from 40% to 50% by day 6. 
The increase in protein (%AFBM) reflected the de- 
cline in lipid and was most evident in the starved 
red drum larvae. Larvae that have been starved con- 
serve protein as musculature until the time of death. 
Conservation of muscular proteins allows the ani- 
mal to swim as long as possible before complete 
muscle atrophy, or “point of no return,” allowing the 
larvae to search out prey in other, possibly more pro- 
ductive, areas. 
The loss of dry mass in starving larvae, compared 
to fed larvae of equal age, reflected the catabolism of 
lipid and protein (Wallace, 1986). A similar, but less 
severe, drop in lipid was observed in all rearing con- 
ditions and has been observed in other species of fish. 
For example, Fraser et al. (1987) found that larval 
Atlantic herring had a lipid level of 23% dry mass 
(176 pg) one day after hatching decreasing to 11% 
(221 pg) by day 16. Those percentages were similar 
to those found for red drum larvae in the present 
study (20.18% to 11.74%) over the first two weeks of 
life. It is likely that lipid serves as a buffer fuel dur- 
ing the early life history of red drum. It is not accu- 
mulated. When high-quality food energy is available 
in excess, larval red drum larvae grow faster rather 
than accumulate an energy reserve. This is best ex- 
emplified by the differences in larvae growing at 25°C 
in the laboratory and 25°C in the ponds. 
Elemental composition agreed well with other pub- 
lished values for red drum (Lee et al., 1988) and lar- 
val herring of similar size (Ehrlich, 1974, a and b; 
1975) as well as with our own results on proximate 
composition (Table 1). Larvae that are growing nor- 
mally, as in the 5.0 prey/mL experiments and the 
ponds, show greater increases in protein than in lipid. 
The increase in %N with age, and the declining %C, 
mirrored the changes (protein increase, lipid de- 
crease) in proximate composition. This changing el- 
emental composition resulted in a declining C:N in 
normally growing larvae. Starving individuals had 
slightly higher C:N than fed individuals as a result 
of their diminished protein synthesis. Larvae raised 
in the ponds have the lowest C:N as a result of the 
high protein levels relative to lipid. Thus, the C:N 
can be used as an indicator of physiological status in 
developing fish. It should be noted, however, that this 
ratio applies in the opposite fashion to adult fish. A 
declining C:N in older fish indicates starvation where 
lipid is laid down as an energy reserve and is com- 
busted before protein. The rapidly accumulating 
musculature of a healthy, growing fish larva results 
in a declining C:N, giving the appearance of starva- 
tion when, instead, this ratio indicates that protein 
is accumulating at a faster rate than lipid. 
