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Fishery Bulletin 95(3), 1997 
Protein-specific growth and biochemical 
indicators 
RMIA-DNA ratio Our values for RNA:DNA fall at the 
low end of the range of ratios reported in the litera- 
ture for larvae reared under a variety of different 
conditions (Ferron and Legget, 1994). Wright and 
Martin ( 1985) found similar RNA-DNA ratios ( 1 to 2 
at 19-2 1°C) for starved striped bass, whereas fed 
striped bass larvae had ratios of 3-3.4 during the 
first two weeks after hatching. Robinson and Ware 
(1988) observed a similar trend in RNA-DNA ratios 
with starvation in the early life of larval Pacific her- 
rings, as we did with red drum; ratios declined up to 
yolk-sac absorption, where the ratios leveled off. Val- 
ues for RNA:DNA obtained in the laboratory in this 
study (1 to 2) were lower than previously reported 
values (2 to 4) for red drum larvae (Westerman and 
Holt, 1994). 
As has been reported previously (Buckley, 1982; 
Ferron and Legget, 1994), the relation of growth rate 
and RNA:DNA changed with temperature. The 
higher mass-specific and protein-specific growth 
rates observed in the laboratory at 25°C, in compari- 
son with those at 20°C and in the ponds at 32°C, as 
well as in comparsion with those at 25°C, were ac- 
companied by lower RNA:DNA values (Tables 1 and 
2). The inverse relation between RNA:DNA and tem- 
perature holds true in field-caught larvae as well. It 
was observed by Setzler-Hamilton et al. ( 1987), who 
found that in late spring, values for RNA-DNA ra- 
tios in striped bass larvae were higher than values 
measured in hotter, early summer months (spring 
values were about 3 and summer values were 2 to 
2.5). 
A high growth rate accompanied by a low RNA- 
DNA ratio, such as we observed in the 32°C ponds, is 
probably due to an increase in the efficiency of ribo- 
somes in initiating protein synthesis and to an in- 
crease in the rate of chain elongation due to a direct 
effect of temperature, i.e., an increase in the produc- 
tion of protein per unit of ribosomal RNA due to a 
Q 10 effect (cf. Westerman and Holt, 1988). Despite 
the effect of temperature on the relation of RNA:DNA 
and growth rate, RNA:DNAis a useful tool for deter- 
mining nutritional status of fish larvae, particularly 
if it is understood that temperature contributes sub- 
stantially to the relationship between RNA:DNA and 
growth (Buckley, 1982: Buckley et al., 1984; Ferron 
and Legget, 1994). 
LDH Activity LDH, the terminal enzyme in verte- 
brate anaerobic glycolysis, is an important factor in 
the ability of some fish to produce sudden bursts of 
swimming and is found in large quantities in white 
muscle (Somero and Childress, 1980). The observed 
increase in LDH activity with age until death of 
starved larvae seems at first glance to conflict with 
priorities expected of an energy-deprived individual, 
in which metabolic processes would be expected to 
be declining. However, it is to be expected that LDH 
activity would be conserved, even in starving larvae, 
so that the muscle would remain functional as long 
as possible. A larva with no capability for movement 
would be doomed; thus, a metabolic investment in 
locomotory capability makes good adaptive sense. 
Unlike in RNA:DNA, LDH activity showed a di- 
rect correlation with both mass- and protein-specific 
growth rate in the two fed laboratory treatments 
despite the increase in temperature from 20°C to 
25°C. In the ponds, LDH activities showed an inter- 
action with temperature similar to that seen in 
RNA:DNA, i.e. a lower specific activity at 32°C de- 
spite a higher growth rate. In the case of LDH, the 
declining activities observed in larvae from the higher 
temperature pond probably indicate that a lower con- 
centration of enzyme is sufficient to maintain the 
catalytic efficiency needed by the tissues at the higher 
temperature (cf. Hochachka and Somero, 1984). The 
fact that a similar drop was not noted in the labora- 
tory suggests a threshold for the drop in activity be- 
tween 25°C and 32°C that was not present in the 
transition between 20°C and 25°C. 
Clarke et al. (1992) found similar values for LDH 
in red drum larvae raised on wild zooplankton. Val- 
ues for LDH activity in Clarke’s study, assuming 87% 
water content, averaged 19-26 units/gWM for two- 
week-old larvae, slightly lower than the values we 
observed in the larvae raised in the laboratory and 
ponds. 
Biochemical parameters as predictive tools 
Although similar in their use as biochemical proxies 
for growth, LDH activity and RNA:DNA are funda- 
mentally different in many other respects. RNA:DNA 
is a ratio of measured quantities, whereas LDH ac- 
tivity is a determination of a rate: a kinetic measure- 
ment. Inherent in the measurement of RNA:DNA is 
the assumption that the methods for determining the 
quantities of RNA and DNA are accurate, but there 
is no direct effect of temperature on the assay itself. 
For LDH, activities are measured in saturating con- 
ditions of substrate, which means that the activities 
are maximal activities (V max from Michaelis-Menten 
kinetics; Lehninger, 1982) for each treatment. It is 
tacitly assumed that if assays are performed in satu- 
rating conditions at the same temperature, the dif- 
ferences in activity, or V max , are due to differences 
in concentration of the enzyme. This assumption is 
