256 
Fishery Bulletin 96(2), 1998 
anic and estuarine summer flounder larvae revealed 
strikingly different patterns (Fig. 4). Early in the 
night, incidence of feeding was much lower in estua- 
rine collections. Fasting during metamorphosis, as 
has been noted in plaice (Riley, 1966; Lockwood 1984; 
Hamerlynck et al., 1989), may have contributed to 
this pattern. Plaice and sole have shown marked 
decreases in food-searching behaviors (distance cov- 
ered per minute and time spent in feeding activity) 
at metamorphosis (Blaxter and Staines, 1971). Late 
at night, at 0400-0559, incidence of feeding in es- 
tuarine collections was double the rate seen in oce- 
anic summer flounder collections (Fig. 4). A lower 
threshold light intensity for feeding at metamorpho- 
sis may have contributed to this, although small 
sample sizes of late-night estuarine collections pre- 
clude overreaching conclusions. Resolution of the 
threshold of light intensity for feeding of metamor- 
phic summer flounder in a controlled laboratory set- 
ting could result in determination of optimal illumi- 
nation levels at metamorphosis in aquaculture. 
Metamorphosis has been considered a critical inter- 
val in the early life of some marine fishes (Thorisson, 
1994). In the present study, the incidence of feeding 
of summer flounder larvae was observed to decline 
with metamorphic development to stage H. This sug- 
gests that the midpoint in the migration of the right 
eye (Keefe and Able, 1993) may be a critical period 
for summer flounder. In a laboratory study, a cessa- 
tion of feeding was observed at stage G (Keefe and 
Able, 1993). However, cessation of feeding at meta- 
morphosis may not place flatfish in any real danger 
of starvation (Lockwood, 1984). Metamorphic plaice 
larvae are capable of surviving without food for 7-25 d, 
without reaching the “point of no return” (Wyatt, 1972). 
Blaxter and Hempel (1963) have defined the “point of 
no return” as the point at which starved larvae become 
too weak to feed. Midmetamorphic summer flounder 
larvae are capable of surviving 56 d without reaching 
the “point of no return” (Keefe and Able, 1993). At meta- 
morphosis and shortly thereafter flatfish may be more 
vulnerable to predation (van der Veer and Bergman, 
1987; Witting and Able, 1993, 1995) than to starvation 
(Thorisson, 1994). 
Acknowledgments 
I would like to thank Mike Fahay, of the NOAA’s 
NMFS James Howard Marine Sciences Laboratory, 
who provided access to oceanic collections and data, 
and Ken Able and Stacy Hagan, Rutgers University 
Marine Field Station, who provided access to estua- 
rine collections and data. A portion of this study was 
supported by the University of Connecticut. 
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