Stehlik: Effects of season on activity rhythms and swimming behavior of Pomatomus saltatrix 
1 
Figure 4 
Still images of gliding bluefish (Pomatomus saltatrix) during the activity study. (A) Numerous gliding fish near the far 
side of the aquarium at night, recorded with a video camera, winter 1996, ( B ) one gliding (top fish) and one side-swimming 
fish (lower fish) close to the window near the video camera, winter 1996, (C) photograph from below a gliding fish, spring 
1995, (D) gliding fish (lighter fish) are keeping pace with vertically oriented fish (gray-toned individuals) in the school, 
recorded with a video camera, spring 2007. 
ing of the school was disrupted and fish dispersed 
with no common direction. Milling fish stayed near 
the water surface, apparently neutrally buoyant, 
and moved extremely slowly, propelled by occasion- 
al gentle flexes of the pectoral fins and tail. Milling 
was noticed beginning 6 February and was common 
through mid-March. Another period of milling occurred 
in the last week of April and the beginning of May dur- 
ing the parasite infestation. 
Discussion 
Feeding and growth 
The period of extremely high food consumption and 
growth per body weight does not last very long in young 
bluefish. In this experiment, food consumption was 
greatest when the fish were smallest, as was anticipated 
from the literature. From 16% body weight per day 
(BW/d) in 35-g fish, food consumption rate decreased 
to 1-5% BW/d in 369-g fish the following spring. Simi- 
larly, in laboratory mesocosms at 21°C, growth rates of 
the smallest, (mean 2.6 g), age-0 fish were as high as 
9.2% BW/d, but those of larger (mean 10.2-g) fish were 
2.7%^ BW/d (Buckel et ah, 1995). In small age-0 field- 
caught bluefish, food consumption rates were >30% BW/d 
(Juanes and Conover, 1994; Buckel et ah, 1995). Rapid 
food intake permits rapid growth to a size where fish 
are less vulnerable to predators. 
Growth in the research aquarium was continuous, 
and the increase in length was comparable to that of 
wild bluefish in the middle-Atlantic states. The fish 
in the aquarium grew to a mean total length of 300 
mm (265 mm FL) by 22 May, whereas wild age-1 fish 
originating from a spring-spawned cohort are about 
250 mm FL when they are caught in spring (Shepherd 
and Packer, 2006). 
