286 
Fishery Bulletin 109(3) 
Table 1 
Types of models and estimated parameters for hatching patterns and posthatch survival of northern rock sole ( Lepidopsetta 
polyxystra) larvae as a function of temperature (2°, 5°, 9°, and 12°C). Analysis was performed on tank means (n= 3—4 tanks per 
temperature) of 15-20 larvae for each tank during each sampling period (/i=4-10 sampling periods). Criteria for model selection 
are found in the Material and Methods section. R 2 = correlation coefficient. 
Variable 
Model type 
Equation and parameters 
df 
F 
R 2 
P 
Days to first hatch 
Exponential decay 
/■(x)=37.516e-° 133x 
1 
353.010 
0.97 
<0.001 
Hatch duration 
Exponential decay 
/'(x)=17.556e~ 0119x 
1 
451.941 
0.97 
<0.001 
Days to peak hatch 
Exponential decay 
/Le)=46.499e-° 136x 
1 
593.968 
0.98 
<0.001 
Hatch quality 
Gaussian 
/’(x)=104.872e -0 ' 6 l 6.023 J 
2 
55.873 
0.90 
<0.001 
Hatch success 
Gaussian 
rte (x- 2 . 194 V 
f(x)=72A54e^{ 6.313 J 
2 
10.587 
0.66 
0.003 
50% mortality (M 50 ) 
Exponential decay 
/U)=9.951 + 39.970e-° 391x 
2 
747.608 
0.99 
<0.001 
Maximum size-at-hatch 
Gaussian 
/lx) = 4.377 + 0.826e“°' 5 [ 3.916 J 
3 
29.336 
0.89 
<0.001 
Discussion 
The temperature effects on hatching patterns (i.e., time 
to first hatch, hatch duration, and time to peak hatch) 
followed an expected negative relationship. Develop- 
ment rates among teleost fish are highly variable and 
largely a function of initial egg size (Pauly and Pullin, 
1988), but temperature ultimately controls the develop- 
ment response curve within each fish species (Pepin, 
1991; Jobling, 1997). Hatch synchrony in fish generally 
decreases with temperature (e.g., Ims, 1990), although 
it can be dependent to some extent on other environ- 
mental variables (e.g., predation; Bradbury et al., 2004). 
Northern rock sole appear to follow this pattern, but 
comparisons of our laboratory data to field data were not 
possible because northern rock sole eggs are demersal 
and have not been collected from the wild. Larvae have 
been captured at the surface during April-August in the 
Bering Sea and Gulf of Alaska when surface tempera- 
tures can vary from -1° to 10°C (Matarese et al., 2003). 
Northern rock sole eggs are difficult to distinguish 
from co-occurring Pacific cod ( Gadus macrocephalus) 
because they are similar in size (0.96-1.10 mm vs. 
0.98-1.08 mm, respectively), demersal, semi-adhesive, 
and have a thick chorion. However, late-stage eggs 
of these species differ in several ways: yolk pig- 
ment is present in northern rock sole, but absent 
in Pacific cod, and postanal pigment on northern 
rock sole embryos consists of a dorsal patch at 
50% SL and a band at 75% SL, whereas Pacific 
cod embryos have pigment bands at both 50% 
and 75% SL. Anal finfold pigment is present on 
northern rock sole embryos below the patch and 
band, but there is no anal finfold pigment on Pa- 
cific cod embryos. 
Cold temperatures (2-5°C) produced larger lar- 
vae at time of hatching, but the effects of egg 
incubation temperature on hatch size in other 
fish species appear to be species-specific. Atlantic 
herring ( Clupea harengus) and Pacific cod also 
produce larger larvae at low temperatures across 
a similar thermal range (Alderdice and Velsen, 
1971; Laurel et al., 2008), whereas walleye pol- 
lock ( Theragra chalcogramma), Atlantic silverside 
(Menidia menidia) and yellowtail flounder (Pleuro- 
nectes ferrugineus) tend to produce larger larvae 
at warmer temperatures (Bengston et al., 1987; 
Blood et al., 1994; Benoit and Pepin, 1999). 
The effects of hatch rank (i.e., an individual’s 
day-of-hatch within a batch of eggs) on size-at- 
hatch and yolk reserves have been measured in 
40 
0 -I , , 1 1 1 T 1 
0 2 4 6 8 10 12 14 
Temperature (°C) 
Figure 3 
The effects of temperature on the number of days to first 
hatching (closed circles), hatch duration (open circles), and 
timing of peak hatching (closed triangles) in northern rock sole 
(Lepidopsetta polyxystra ) eggs. Data are means (±1 standard 
error [SE]) based on 2 mL of eggs in three replicate tanks 
at each of the following temperatures: 2°, 5°, 9°, and 12°C. 
