Laurel and Blood: The effects of temperature on hatching and survival of larval Lepidopsetta polyxystra 
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a number of species, but the ecological signifi- 
cance is poorly understood. Like northern rock 
sole, late-hatching larvae in other marine spe- 
cies are generally larger and have smaller yolk 
sacs (e.g., capelin [Mallotus villosus], Chambers 
et ah, 1989; wolffish [Anarhichas lupus], Ringo 
et ah, 1987). Methven and Brown (1991) also 
showed similar effects on hatch rank for ocean 
pout ( Macrozoarces americanus), but this pat- 
tern was only observed at low temperatures 
when the hatching period was extended. Al- 
ternatively, late-hatching Atlantic silverside 
larvae are smaller than earlier hatching larvae 
(Bengston et ah, 1987), although this occur- 
rence appears to be a rare exception. Interest- 
ingly, despite the increased attention on paren- 
tal effects on offspring size variation in marine 
fish (e.g., ~1 mm size range variation 13.8-4.8 
mm SL] in Atlantic cod [ Gadus morhua ] larvae, 
Paulsen et ah 2009), the role of hatch rank 
and temperature cannot be ignored because 
they appear to account for an equivalent (if 
not more) amount of variability in offspring 
size from a single parent (~2.5 mm size range 
variation [2.95-5.43 mm SL], this study). 
From an evolutionary perspective, the pro- 
duction of offspring of variable size and yolk 
reserves may be a bet-hedging strategy in a 
variable environment of temperature, food 
availability, and predator risk. However, in fish 
larvae, the survival benefits have seldom been 
tested explicitly beyond a few case studies. In 
walleye pollock, early-hatching larvae had high- 
er growth potential than late-hatching larvae 
(Porter and Bailey, 2007). Similar results have 
been reported for early-hatching Atlantic her- 
ring larvae (Geffen, 2002), although this effect 
is short-lived because early- and late-hatching 
Atlantic herring larvae have overlapping size- 
at-age and growth trajectories shortly after 
the onset of exogenous feeding (Panagiotaki 
and Geffen, 1992). In general, smaller early- 
hatching larvae likely have under-developed 
sensory organs, swim capabilities, and digestive 
enzymes to immediately handle feeding exoge- 
nously (Porter and Bailey, 2007). As a tradeoff, 
these larvae may have an extended capabil- 
ity for surviving in the absence of food given 
their larger yolk reserves (Laurel et al., 2008). 
The latter feature also appears to be true for 
northern rock sole. Although eye diameter was 
not significantly larger in late-hatching larvae, 
there was a weak trend in increased eye diam- 
eter and increased eye pigmentation to indicate 
increased visual development with late hatch- 
ing. More importantly, as has been shown with 
several gadid species, yolk reserves in northern 
rock sole were larger in early hatching larvae. 
Increased yolk reserves in early-hatching Pa- 
cific cod larvae allowed individuals to live 3-8 
100 - 
80 - 
20 - 
Temperature (°C) 
Figure 4 
The effects of temperature on hatch quality (dark circles) and 
hatch success (open circles) of 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. 
Figure 5 
The effects of temperature and hatch time (days into hatch cycle) 
on northern rock sole ( Lepidopsetta polyxystra) larval size-at- 
hatch (standard length [SL] mm). Values for SL are means (±1 
standard error [SE]) based on image analysis of larvae taken 
from three replicate tanks (10-15 larvae sampled per tank). 
