Brightman et ai: Energetics of larval Sciaenops ocellatus 
443 
a reasonable one. It is important, however, to be 
aware of other potential causes of variability in the 
relation of both RNA:DNA and LDH activity to 
growth or condition in fish larvae. It has been dem- 
onstrated here and elsewhere (Ferron and Legget, 
1994) that rearing temperature alters the relation 
of growth and biochemical proxies for growth. An- 
other potential source of variability in the relation is 
the scaling of each of the proxies with individual size. 
RNA:DNA increases slightly with individual size 
(Buckley, 1982) but overall is insensitive to the 
changes in individual mass that would be expected 
in a study of larval fish growth within a single field 
sample. This is not the case for LDH activity which 
scales strongly with mass in fishes (e.g. Somero and 
Childress, 1980; Torres and Somero, 1988). In this 
study, a significant relation was observed between 
LDH activity (y, units/gWM) and protein mass (x, pg 
protein): y = 2.25x 0187 ; P=0.02; r 2 =0.43. RNA:DNA 
showed no significant change with size. Our study 
suggests that, for maximum accuracy, direct compari- 
sons of field-caught larvae for LDH activity are best 
confined to narrow size ranges or the relation be- 
tween LDH and size is described empirically. On the 
other hand, it could be argued that since mass-spe- 
cific LDH activity increases with increasing mass, it 
is actually incorporating a growth-specific change 
within its scaling behavior, making it a better proxy. 
Either way, it shows considerable potential. 
Acknowledgments 
The authors would like to thank Bill Falls, Anne 
Burke, and Dan Roberts of the Florida Marine Re- 
search Institute for providing red drum larvae and 
for considerable help in teaching us culturing tech- 
niques. This research was supported by DNR con- 
tract C-7701 and NSF OCE 92-18505 to J.J. Torres, 
and NSF OCE 92-17523 to M.E. Clarke. 
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