4 
Fishery Bulletin 107(1 ) 
Table 2 
Light, temperature, and biological measurements of bluefish ( Pomatomus saltatrix ), 1995—96. Seventeen weeks are presented in 
which observations of swimming were made at each hour of the day and averaged for the week. Total lengths and weights were 
calculated from subsamples measured on the dates in Table 1. All other quantities, hours of light per day, water temperature (°C), 
food consumption in percent body weight per day (% BW/d), and swimming speeds in cm/s and body lengths per second (BL/s), 
were averaged for the week. 
Week 
First day 
of week 
Number 
of fish 
Light 
(hr/d) 
Mean 
temperature 
(°C) 
Bluefish 
total length 
(mm) 
Bluefish 
weight i 
(g) 
Food 
consumption 
(% BW/d) 
Swimming 
speed 
(cm/s) 
Swimming 
speed 
(BL/s) 
7 
10 Sep 
89 
12.6 
20.7 
198.3 
78.8 
13.0 
35.8 
1.81 
11 
8 Oct 
72 
11.4 
19.2 
228.2 
137.3 
8.8 
38.3 
1.68 
14 
29 Oct 
72 
10.5 
17.9 
242.0 
170.0 
9.3 
40.0 
1.65 
18 
26 Nov 
71 
9.6 
15.3 
254.7 
201.3 
4.1 
33.6 
1.32 
20 
10 Dec 
71 
9.4 
15.1 
257.7 
206.3 
3.8 
31.2 
1.21 
23 
31 Dec 
71 
9.4 
15.0 
262.3 
214.1 
2.5 
35.0 
1.33 
27 
28 Jan 
71 
10.1 
15.0 
269.3 
225.9 
3.1 
38.5 
1.43 
31 
25 Feb 
71 
11.2 
15.0 
277.2 
239.3 
3.1 
34.8 
1.25 
32 
3 Mar 
71 
11.6 
15.0 
279.2 
242.8 
2.0 
34.3 
1.23 
33 
10 Mar 
71 
11.9 
15.0 
281.2 
246.3 
2.2 
31.1 
1.11 
34 
17 Mar 
71 
12.2 
15.0 
283.3 
249.9 
3.6 
37.0 
1.31 
35 
24 Mar 
70 
12.5 
15.0 
285.3 
253.6 
2.1 
46.0 
1.61 
36 
31 Mar 
69 
12.8 
15.0 
287.4 
257.2 
3.2 
45.0 
1.56 
40 
28 Apr 
67 
13.9 
15.5 
295.8 
272.5 
0.9 
38.2 
1.29 
44 
26 May 
67 
14.8 
17.2 
306.3 
298.1 
4.7 
44.2 
1.44 
46 
9 Jun 
67 
15.0 
19.2 
315.3 
330.4 
4.5 
51.2 
1.62 
47 
16 Jun 
67 
15.0 
20.4 
319.9 
347.9 
5.9 
53.3 
1.67 
in late March with increase in dajr length, although 
temperature was unchanged. When bluefish measured 
about 285 mm in late March, their mean speeds rose 
above 40 cm/s and they became capable of much higher 
maximum speeds. In June 1996, swimming speeds in 
cm/s were significantly greater than those in Septem- 
ber 1995 (/-test, P<0.01, both at 20°C). Speeds in body 
lengths/s, however, showed no trend during the experi- 
ment (Table 2), because larger fish can swim faster. 
When twilight speeds were removed from the dataset, 
there was no overlap in day and night speeds (cm/s) 
or their standard deviations (Fig. 3). In fall, the mean 
speed during daylight was >52 cm/s, and the mean 
night speed was between 28 and 38 cm/s. The decrease 
in mean speed in winter (Fig. 2), particularly in Janu- 
ary, was due only to decreased day speed and briefer 
periods of peak activity (Fig. IB). Night speeds were 
similar all year, except for certain periods of extremely 
slow swimming in spring, as described below. By mid- 
June, at the end of the study, the difference between 
day and night activity was greater because the mean 
daylight speed increased to 68.6 cm/s. 
Modes of swimming 
Bluefish used various modes of swimming in the research 
aquarium (Table 3). The most prevalent mode was pow- 
ered swimming, which they performed by propelling 
themselves by beats or contractions of the muscles of the 
rear of the body and caudal peduncle. During powered 
swimming, the body orientation was vertical, while 
the pectoral and pelvic fins were folded except to make 
adjustments in direction. Fish in the aquarium used 
this mode primarily while circling in a level horizontal 
ring. At other times, powered swimming in a vertically 
undulating or sine-wave-like pattern was observed at all 
depths of the aquarium. The entire school participated 
in this behavior, often for hours. 
During periods of undulatory swimming, some fish 
glided on their sides. To glide, a bluefish rolled onto its 
side, ceased body and tail movement, and its momentum 
carried it gradually downward (Figs. 4 and 5). The body 
was held flat or in a slightly convex shape. The dorsal, 
anal, and pelvic fins were stretched out and curved up 
or down slightly in response to water flow or for chang- 
ing direction. The pectoral fins were pointed outward 
and sometimes sculled or steered, the tail was still, 
and the tail fin lobes were curved up or down slightly. 
The body rolled by less than 90° (i.e., not parallel to 
the bottom). Either side might be oriented downward 
and a fish sometimes switched sides in mid-glide. A fish 
encountering a side of the aquarium sometimes turned 
and continued to glide downward. Only a few members 
of the school glided at one time, and they accompanied 
