Hurst et al.: Growth rates of Gadus macrocephcilus 
387 
Table 2 
Stage-specific growth models for early life stages of Gulf of Alaska Pacific cod ( Gadus macrocephalus) . Models describe growth in 
mass ( g M ) and length ( g L ) as a function of temperature (T) for each stage, r 2 is the coefficient of determination. 
Stage 
Growth functions 
r 2 
Eggs-embryos 
temperature range: 0-8°C 
dry weight (fig) 
g M = 3.807 + 1.493 • T- 0.032 ■ T 2 
0.929 
standard length (mm) 
g L =0.104 + 0.024 • T- 0.00002 • T 2 
0.939 
Preflexion larvae 
temperature range: 2-ll°C 
dry weight (fig) 
g M = 2.990 + 0.772 • T- 0.077 • T 2 
0.897 
standard length (mm) 
g L = 0.179 + 0.015 • T - 0.0001 ■ T 2 
0.941 
Postflexion larvae 
temperature range: 3-1 1°C 
dry weight (g) 
g M = 1.652 + 1.059 • T - 0.028 • T 2 
0.830 
wet weight (g) 
g M = 0.531 + 0.857 • T - 0.024 • T 2 
0.897 
standard length (mm) 
g, =0.034 + 0.043 • T- 0.0008 ■ T 2 
0.882 
total length (mm) 
g L = 0.044 + 0.019 • T- 0.001 • T 2 
0.889 
Juveniles 
temperature range: 2-12°C 
wet weight (g) 
g M =- 0.998 + 0.579 • T- 0.022 • T 2 
0.826 
total length (mm) 
g L = -0.081 + 0.079 • T - 0.003 • T 2 
0.762 
temperature-dependence function, differing only in ele- 
vation through ontogeny (Fig. 4). 
Growth rates of Pacific cod through the early life 
stages were described by the equations 
§ l ~ 
0.076 + 0.029 T - 0.00002 T 2 
0.076 + 0.029 • T - 0.00002 T 2 
f 0.0758 
1-0.059/e s 
if stage = embyro 
if stage > embryo 
allometric scaling, wherein growth rates after hatching 
are lower than those predicted by body size allometry. 
We determined parameters for temperature-dependent 
growth functions in length and mass for specific life 
stages and for a unified STDG function. These measures 
of growth potential can be used to evaluate the biotic 
and abiotic factors regulating the growth and survival 
of early life stages of Pacific cod in the wild (Folkvord, 
2005; Hurst et al., 2010). 
and 
(0.454 + 1.610 T- 0.069 T 2 )- 
g-6.725 Md _j_ 3 705 if stage = embryo 
8m = ' (4) 
(0.454 + 1.610 T - 0.069 T 2 )- 
g - 6.725 m d if stage > embryo 
These equations explained over 88 % of the observed 
variance in growth rates of Pacific cod embryos to post- 
settlement juveniles (g M r=0.969; g L r=0.940). Analysis 
of residuals from these models indicated greater vari- 
ance at higher growth rates (small body sizes and higher 
temperatures), but there were no trends in residuals in 
relation to experimental temperature or body size that 
would indicate significant departures from the model. 
Discussion 
Temperature is the dominant regulator of growth in 
early life stages of fishes. In this study we examined 
the ontogenic pattern in growth rate for early life stages 
of Pacific cod. We demonstrated a deviation from strict 
Experiments 
Because these experiments were conducted across a 
range of life stages, many aspects of our experimental 
method had to be adapted for each specific experiment, 
such as tank volume, prey type, and fish density. How- 
ever, the most significant differences in method between 
egg-larval and juvenile experiments were the level of 
observation and source of fish. To estimate growth rates 
of embryos and larvae, subsamples of fish were drawn 
from a large tank population to determine mean size at 
a specific age (Otterlei et al., 1999; Monk et al., 2008). 
Change in mean size at age was then used to determine 
growth rate in each replicate tank. With this approach, 
there is the potential for size-selective mortality in the 
experiments to affect estimates of mean growth rates. 
Such size-selective mortality is most commonly assumed 
to be the result of predation (including cannibalism 
in single species culture). However, such an effect is 
unlikely to have occurred in these experiments: postflex- 
ion larvae were sorted by size before growth experiments 
specifically to avoid potential cannibalism, and we saw 
no evidence of cannibalism in the experiment (no larvae 
in samples with fish in their stomachs). Because juvenile 
fish could be handled, they were measured and returned 
to the tank and subsequently remeasured, providing 
