388 
Fishery Bulletin 108(4) 
°-6 I A 
O 0.1 T 
0.0 I T T T ^ 
2 4 6 8 10 
Figure 3 
Temperature-dependent growth rates of postsettlement 
juvenile Pacific cod (Gadus macrocephalus) in (A) total 
length and (B) wet mass. Fish used in the experiment 
were collected from nearshore nursery areas at Kodiak 
Island, Alaska in July 2008. Values are the mean growth 
rates (± standard error) for three replicate tanks at 
four temperatures. Symbols represent groups based 
on initial size sorting of fish (circle: small; triangle: 
medium; square: large). Overlapping points are displaced 
horizontally for clarity. 
growth trajectories for individual fish. These individual 
growth rates were then averaged to estimate mean 
growth rates of fish in each tank (Hurst and Abookire, 
2006; Wijekoon et ah, 2009). 
For experiments with eggs and larvae, we used the 
offspring of field-caught spawning adults. In each year 
of experiments, gametes from one or two females were 
mixed with those of three to five males. Juvenile fish 
used in experiments were naturally produced and cap- 
tured after recruitment to juvenile nearshore habitats. 
Therefore, the genetic diversity among experimental ju- 
veniles was significantly greater than that found in ex- 
perimental eggs and larvae. This difference in potential 
genetic contributions to growth rates is not expected to 
have a significant influence on the overall growth pat- 
terns described here because maternal and genetic ef- 
fects on growth have been shown to be small in relation 
to environmental factors such as temperature (Benoit 
and Pepin, 1999; Green and McCormick, 2005) and prey 
availability (Clemmesen et al., 2003). 
Ontogenetic patterns of growth 
By combining results across life stages, we clarified 
ontogenetic patterns in growth and length. With the 
exception of a departure during the preflexion stage, 
growth patterns followed expected size-dependent allo- 
metric patterns throughout much of the early devel- 
opment (Elliott and Hurley, 1995). Growth in mass 
(g M ) decreased with increases in body size (Wootton, 
1990) and growth in length (g L ) was constant across life 
stages. Although the constancy of g L across a range of 
body sizes in early life stages has been noted in other 
studies (Jones, 2002; Sigourney et al., 2008), those 
experiments have not generally included the presettle- 
ment egg and larval stages incorporated here. Interest- 
ingly, in Pacific cod, the general pattern of across-stage 
similarity in g L extended from the egg-embryo stage 
into the juvenile stage. 
There was a significant departure from the expect- 
ed ontogenetic pattern in the preflexion larval period, 
most clearly observable in the g L results. Measured g L 
among preflexion larvae averaged only 41% of the rates 
measured for embryos, postflexion larvae, and settled 
juveniles. Although less readily apparent, a similar de- 
parture was observed in mass growth as the decline in 
g M between the egg-embryo and preflexion larval stages 
was greater than expected from allometric patterns 
accounting for the observed differences in body size. In 
several studies on the growth of first-feeding gadids, 
higher growth rates were reported for fish reared on 
copepods than on cultured rotifers (Conceicao et al., 
2010). Unfortunately, technical limitations preclude 
rearing sufficient quantities of copepods for use in ex- 
periments such as ours. For our study, larval Pacific cod 
were reared on essential-fatty-acid-enriched rotifers, as 
the best of the practicable prey alternatives. Therefore, 
it is possible that growth rates of preflexion larvae are 
under-estimates of maximum potential growth at this 
stage. However, the effect of prey type is insufficient to 
completely explain the significantly lower growth rate 
observed at this stage when compared to other stages. 
Further, similar observations of reduced growth rates of 
fishes in the early posthatch phase have been observed 
in several other studies. Experiments in which growth 
of haddock ( Melanogrammus aeglefinus; Martell et al., 
2005) was tracked through the egg-larva transition 
revealed a similar reduction in growth associated with 
hatching. A similar pattern is apparent in Atlantic 
cod, but without measurements of embryonic growth 
rates, the magnitude of decline at hatching could not 
be determined (Otterlei et al., 1999; Folkvord, 2005). 
However, these studies document a period of increas- 
ing growth rates after hatching, followed by growth 
rate declines along allometric expectations, indicating 
a similar overall pattern. 
