516 
PACIFIC SCIENCE, VoL XX, October 1966 
faded. The yellow coloration also occurred 
while C. hip purus were struggling on a hook 
and line or lying on the deck just after capture. 
The broad dark vertical bars described by 
Strasburg and Marr (1961, Copeia 1961 (2): 
226-228) were observed in the tank only once 
and then they were faint. These alternate dark 
and light vertical bars about 5 cm wide formed 
on the lateral surfaces of the C. hippurus when 
a live 2 5 -cm Tilapia mossamhica was tossed into 
the tank after the hippurus had not been fed 
for 10 days. The bars were displayed during an 
attack by the hippurus which ended with the 
consumption of the T. mossamhica. A more 
prominent barred coloration was observed at 
sea after chopped meat was tossed in front of 
two hippurus swimming around the observation 
raft, and while the hippurus were attacking 
species of smaller fishes congregated at the 
raft. 
The hippurus in the tanks swam continuously 
day and night with an undulating body move- 
ment, mouth agape and pectoral fins extended. 
During turns of 90° or sharper, the dorsal fin 
was raised slightly. The left pelvic fin was ex- 
tended during gradual left turns ; the right 
during gradual right turns. The typical swim- 
ming speed of a 7 1.1 -cm hippurus, measured on 
three different days over a one-week period, 
was 56.3 cm/sec (0.79 body length/sec) (95% 
confidence interval: 54.8-57.8 cm/sec; n = 31 
30-sec observations, s 2 = 19-32). At this 
speed approximately 50 km would be tra- 
versed in a 24-hr period. The typical tail-beat 
frequency was 1.21 beats/sec (95% confidence 
interval: 1.10-1.32 beats/sec; n = 31, s 2 = 
0.09256). A tail beat is defined as a complete 
cycle back and forth. At the typical speeds the 
fish was moving 46.5 cm/tail beat or 0.654 body 
length/tail beat. Motion pictures taken from the 
raft showed the average tail-beat frequency of 
C. hippurus about 100 cm in fork length swim- 
ming near the raft to be 1.20 beats/sec (95% 
confidence interval: 1.14-1.27 beats/sec; n = 8, 
s 2 = 0.009143), essentially the same as in the 
tank. The surface temperature was 27° C, only 
3° C higher than the daytime tank temperatures. 
These slow rates of swimming are those most 
commonly observed for C. hippurus both in 
tanks and at sea. Since they never stop swim- 
ming, these are as close to resting speeds as the 
animal attains. These dolphins apparently irri- 
gate their gills by forward progression through 
the water and maintain swimming depth by the 
hydrodynamic lift exerted against the pectoral 
fins. They do not have a gas bladder. These 
same functional components (respiration and 
hydrostatic equilibrium) of locomotion in pe- 
lagic fishes have been noted previously for 
scombrids (Breder, 1926, Zoologica 4(5) :159- 
297; Hall, 1930, Am. J. Physiol. 93(2) :4l7- 
421; Magnuson and Prescott 3 , Nakamura, op. 
cit.) and are probably a very common adapta- 
tion of locomotion in pelagic fishes. 
Several characteristic behavior patterns were 
observed among the C. hippurus in captivity. 
These were named mouth closure, oral valve 
closure, yawn, lean, chafe, jerk, and defecation. 
All of these, plus surfing, also were observed at 
sea. Their occurrence both in captivity and at 
sea suggests that they are naturally occurring 
behavior patterns in the repertoire of C. hip- 
purus. A brief description of each, based pri- 
marily on the tank observations, is presented 
here. 
Mouth closure. The mouth is closed com- 
pletely for 1-5 sec and then reopened to the 
typical 2- to 5 -cm gape. 
Oral valve closure. For periods of less than 
1 sec, the mouth is closed partially from the 
typical gape in such a way that the oral valve 
appears to close completely. The mouth then is 
reopened to the typical gape. 
Yawn. The mouth is opened maximally, the 
gular region is depressed, the opercles are flared, 
all fins are extended, and all caudal motion is 
stopped. Typical posture and locomotion are 
disrupted for 3-4 sec. 
Lean. The body is tipped to the side at angles 
of 45-90°. Sometimes this results during a turn 
as a continuation of a banking posture, but occa- 
sionally it results from a quick tipping move- 
ment while following a straight course. Then 
the dorsal fin is extended, as are the pectoral 
and pelvic fins on the side toward the surface. 
3 Magnuson, John J., and John H. Prescott. 1966. 
Courtship, locomotion, feeding and miscellaneous be- 
haviour of Pacific bonito ( Sarda chiliensis ) . Anim. 
Behav. 14 ( 1 ) : 54-67. 
