465 
Abstract— Foraging behavior and prey 
abundance are significant factors deter- 
mining the survival success of fish 
during the larval stage. Witch flounder 
( Glyptocephalus cynoglossus) are re- 
ported to have the longest pelagic stage 
of any northwest Atlantic flatfish. We 
used laboratory experiments to investi- 
gate the behavior and performance of 
witch larvae in relation to prey avail- 
ability during this important life his- 
tory stage. In one experiment, larvae 
were reared at a range of prey densities 
(2000, 4000, and 8000 prey per liter) 
and their growth and survival were 
monitored for 12 weeks after hatching. 
In a second experiment the foraging 
behavior of larvae was recorded during 
feeding trials at a range of prey densi- 
ties (250, 500, 1000, 2000, 4000, 8000, 
and 16,000 prey per liter) during weeks 
2-8 after hatching. The larval search 
strategy for prey appeared to change 
from one that was saltatory to one that 
was cruising, and the foraging behavior 
was not strongly affected by variation 
in prey availability. The growth rate 
was rapid (0.53 mm/d) and was unaf- 
fected by changes in prey density as was 
survival. Witch flounder larvae likely 
have low prey requirements compared 
with yellowtail flounder and Atlantic 
cod reared under similar laboratory 
conditions. The ability to forage effec- 
tively when prey is abundant or scarce 
and the low prey requirements of this 
species may be an adaptive response to 
the extended larval period. 
Manuscript accepted 5 February 2001. 
Fish. Bull. 99:465-474 (2001). 
The behavior, growth, and survival of 
witch flounder ( Glyptocephalus cynoglossus) larvae 
in relation to prey availability: adaptations to an 
extended larval period 
Jessica Rabe 
Joseph A. Brown 
Ocean Sciences Centre 
Memorial University of Newfoundland 
St. John's, Newfoundland, Canada A1C 5S7 
E-mail address (for J A Brown, contact author): |abrown@morgan.ucs.mun.ca 
The effects of prey abundance on the 
behavior, growth, and survival of witch 
flounder ( Glyptocephalus cynoglossus, 
Linnaeus) larvae were examined by 
using laboratory experiments. Witch 
flounder is an interesting study organ- 
ism because it displays a life history 
characteristic that is very different from 
other Pleuronectiformes. Most flatfish 
undergo metamorphosis at a small size 
and early age (see Miller et al., 1991; 
Osse and Van den Boogaart, 1997). 
Little information is available on witch 
flounder larval biology and ecology, and 
on precise length and age data at meta- 
morphosis for witch flounder are lacking 
in the literature. However, field evi- 
dence indicates that witch flounder has 
the longest pelagic stage of any North- 
west Atlantic flatfish and undergoes 
metamorphosis at a relatively large 
size (Scott and Scott, 1988). Because 
of their long larval period, witch floun- 
der larvae will likely be exposed to 
temporal variations in prey abundance 
at sea. Larvae are likely able to cope 
with large fluctuations in prey avail- 
ability and may not be as susceptible 
to mismatches in prey abundance or 
starvation in relation to other species. 
Unfortunately, no information is avail- 
able concerning the performance of 
witch flounder larvae in relation to the 
availability of prey in the wild. There- 
fore, we used laboratory experiments 
to gain an understanding of the early 
biology of this species. The objective of 
our study was to determine the growth, 
survival and foraging response of witch 
flounder larvae to differences in prey 
abundance. 
Materials and methods 
Eggs and milt of adult witch flounder 
in spawning condition were collected 
aboard a commercial fishing vessel in 
the Gulf of Maine. The eggs from ap- 
proximately 10 females were fertilized 
with milt from an equal number of 
males. Fertilized eggs were shipped on 
ice by courier to the Ocean Sciences 
Centre of Memorial University of New- 
foundland in Logy Bay, Newfoundland. 
Upon arrival, the eggs were stocked in 
250-L cylindroconical upwelling incu- 
bators at 12°C. Larvae hatched over a 
one-day period, seven days after fertil- 
ization (day 0 of the experiment). At 
this point, 10 larvae were sampled for 
morphometric measurements (defined 
below). 
Two experiments were designed to 
obtain the most information possible 
from the limited number of larvae 
available. In experiment 1, larvae were 
reared at a range of prey densities and 
their growth and survival were moni- 
tored. In experiment 2, larvae were ex- 
posed to a range of prey densities and 
their behavior was recorded. 
We recognize that designing ecologi- 
cally relevant laboratory experiments 
is difficult (Suthers, 2000). Our rearing 
conditions were chosen on the basis 
of established techniques for other 
north Atlantic marine fish larvae that 
have resulted in high growth and sur- 
vival (Puvanendran and Brown, 1999; 
Rabe and Brown, 2000). Although these 
rearing conditions do not precisely mim- 
ic a natural environment, they do en- 
able valid comparisons of experimental 
