Some
aspects of the behavior of the blennioid
fish
Chaenopsis
ocellata Poey
C Robins, C Philllips, F hillipps
The marine laboratory, University Miamin,
USA
Introduction : three individuals (two
males and a female) of Chaenopsis ocellata
Poey, the pike blenny, were captured during
January, 1958, and were placed in an aquarium.
Studies were conducted both at The Marine
Laboratory and the Miami Seaquarium. During the
course of the study the two males were killed by
crabs inadvertently introduced into the tank,
but each was replaced within a few days. One
male measured 73 mm. in standard length; the
other males were about the same length and the
female was about 10 mm. smaller. Detailed notes
were recorded at irregular intervals for six
months and more casual observations were made
nearly every day.
Resting behavior : In normal resting
position the pike blenny lies on the bottom with
its body in a sine or simple curve. The head is
raised sharply and swung from side to side as
other fish or invertebrates attract its
interest. The foreparts are slightly elevated
and are supported by the pelvic fins. In resting
position the dorsal fin is fully depressed, the
transparent pectorals are spread, held
stationary or fanned slowly and aid in
supporting or steadying the body. In its normal
habitat, however, it is doubtful whether
Chaenopsis is often found in the open.
For more than a month the blennies lived in
an aquarium with an ample supply of sand and
food. No tubes were constructed nor did the fish
make any effort to burrow. Tubes of the
terebellid worm, Loimia medusa (Savigny), were
placed in the aquarium and were immediately
occupied by the pike blennies. The blenny would
slowly approach the tube and peer directly into
the opening, which was about 20 mm in diameter.
The approach was always directly toward the
opening, never from the side. If the tube was
empty, the dorsal fin was kept depressed and the
blenny reversed its position with its head about
one-third to one-half of the body length in
front of the opening. The body was then drawn up
in a series of curves until the caudal fin was
about at the level of the tube opening. Entrance
into the tube, always tail first, is like the
action of a person groping blindly for some
object behind him. Here the caudal fin does the
groping until contact is made with the tube, at
which time the blenny uncurls and slides
backward into the tube. This action rarely
accomplishes its objective on first try. More
often, the blenny ends up tight against the out
side of the tube. After a few seconds of rest it
suddenly seems aware that all is not well, at
which time the entire act, starting with the
eyeing of the tube entrance, is repeated until
the attempt is successful; on one occasion six
tries were required. After a first unsuccessful
effort the blenny may peer into the tube from
the side rather than make an entirely new
approach, although this too may be done,
especially if the blenny is distracteil in the
interim. [...]
Respiration by the resting pike blenny is
slow and not conspicuous; ie., the mouth is not
gaped and only a small upper portion of the gill
opening is utilized. As noted above, the
pectoral fins usually are held motionless and
braced against the bottom but are fanned,
apparently for stability, if the blenny raises
off the bottom.
The blennies were never observed to burrow
in the sand or to bide under objects. When
resting on open sand the fanning pectorals
create a broad, shallow depression about the
blenny. If the tube entrances are blocked with
debris, the blenny will push its head through
and reconnoiter for a few seconds. Then it moves
farther forward and vigorously fans the
pectorals and sometimes also the pelvics. The
sand is swept away and larger objects are shoved
aside with the snout and side of the head.
Threat behavior : The approach of any
animal or even drift material within about ten
inches excites the interest of the pike blenny.
Its head is raised and the dorsal fin, except
for the first several spines, is erected. A
slight increase in the respiratory rate is
observed and the dorsal fin and head may darken
slightly. As the organism drifts by or swims off
the dorsal fin is lowered. Closer approach by a
second pike blenny results first in the interest
behavior noted above and then, if further
approach is made, in threat. The transition is
marked by a rapid increase in the respiratory
rate, an intense darkening of the spinous
portion of the dorsal fin and of the head,
spreading of the pectoral fins and finally by
a wide gaping of the mouth and spreading of
the azure branchiostegal membranes. Gaping as an
expression of threat is well known in fishes.
Walters & Robins noted differences in
coloration of the oral cavity in two species of
toadfish. The pike blennies may afford a similar
example, for the oral cavity of C. ocellata is
pale, that of C. alepidota black. Threat display
is never followed directly by an attack. In most
instances, especially where the intruder was
smaller, the warning display sufficed to deter
its approach. No instance of deferred combat as
described by Raney (1947: 127) or Reighard
(1910: 1128) for cyprinid fishes was seen in
Chaenopsis.
The approach of a female pike blenny was
usually ignored by the male. The female,
according to Longley & Hildebrand (1941:
275) is readily distinguished by its lower and
paler spinous dorsal fin and in details of
coloration already described. The large
supralateral eyes of the blenny may be rotated
and tilted with remarkable freedom. From its
behavior, the writers conclude that this blenny
depends largely on sight in its activities.
Attack behavior : Continued approach
of a pike blenny results in aggressive behavior.
Once triggered, the attack is carried to
completion even if the intruder is removed. Both
blennies exhibit rapid respiration with slight
and rapid opening and closing of the mouth. The
branchiostegals are slightly spread and the
dorsal fin is fully erected. The orange and blue
area between the first two dorsal spines is
exposed and by twisting the first two spines
laterad of the others this color mark is
dirécted forward and toward the intruder.
To this point both blennies show the same
behavior except that the intruder does not
exhibit the prefatory threat cycle. If the
intruder approaches rapidly, the defending male
goes directly into attack behavior. The two
blennies meet snout to snout and then raise the
anterior two-thirds of their bodies well off the
substrate, the tails being curled on the bottom
for support.
The mouths are gaped enormously, in
contact with each other, the branchiostegal
membranes spread fully and the pectorals fanned
rapidly to maintain position. If the combatants
are nearly equal in size, the two may rise and
falI in combat several times, never losing their
oral contact. A smaller male is usually subdued
rapidly on the first rising contact, but here it
must be noted that a much smaller male, uniess
it is the defendant, is usually discouraged by
the earlier warning display. In the aquarium a
small male was forced into combat, a situation
that presumably would not occur in nature, by
moving one bienny into the territory of the
second, usually with a probe or plate of glass.
The winning male is the one that suddenly shifts
its mouth sideways across the other's and clamps
down hard. At this point the defeated male folds
his dorsal fin and branchiostegal membranes and
contact is broken as both males drop to the
bottom. Immediately the defeated male resumes
the normal slow respiratory rate and after a few
seconds retreats. The victor maintains rapid
breathing and keeps the dorsal erected but the
branchiostegal membranes are folded. No
additional attack is made on the defeated blenny
even though it may remain nearby for a few
seconds. Return to resting behavior on the part
of the victor is not accomplished for several
minutes, although the color spot in the dorsal
fin is covered after a few seconds. Unlike the
behavior of other fishes (Raney et al., 195
3:99), the defending pike blenny apparently does
not have an advantage over the intruder; the
winner is determined by size and aggressiveness
alone. The pike blenny defending a worm tube is
in quite a different position and is seldom
displaced by a larger aggressor except as noted
later. Attack frorn the shelter of a worm tube
does not differ frorn that described above. The
defending blenny does not completely leave the
tube, however, unless beaten. In some instances
the defending blenny would be doubled back over
the worm tube when fighting off an intruder. A
male blenny would tolerate a female in the other
end of the tube (i.e., a horizontal tube) since
it was long enough to accommodate both. In one
instance the second male occupied the other end
of the tube for a few moments.
The pike blenny readily abandons its tube
when outside pressure is applied. By this method
we chased the larger male frorn his home and
allowed the second and smaller male to enter.
The original male was then returned to the tank.
Although a second and empty tube was available
he returned to the original tube and when the
second blenny was sighted therein, displayed the
attack pattern. The second blenny had retreated
into the tube so that only the tip of its snout
showed. The attacker raised his body on the
pelvic fins, erected the dorsal fin and directed
the orange dorsal spot toward the tube opening.
The first two or three spines may be twisted to
either side in directing the flash spot forward.
When the second male made no effort to join the
fight, the attacker swam to the tube, the motion
being best described as a strike from a coiled
position, and very snake-like. Its mouth was
opened wide, the tip of the lower jaw on the
sand and the upper jaw well above the tube. The
dorsal fin and branchiostegals were still
broadly displayed. Next the mouth was clamped
suddenly and strongly down over the snout of the
"defending" blenny, the action resulting in a
partial folding of the branchiestegal membranes.
Fig. 8,shows the action nearly completed. The
defending blenny erupted from the tube, speeded
by several snaps of the aggressor, and fled over
the tube to the far end of the aquarium. Such
rapid swining is accomplished by anguilliform
movements with the vertical fins depressed.
After a minute the victor entered the tube,
employing the behavior described earlier. In
some instances the defending male remained
completely in the tube, at which tirne the
attacker yanked several pierces from the tube
entrance and pressed its attack into the tube
with the same end result.
Other species of fishes elicited varied
responses. Two common grass flat inhabitants,
Callionymus calliurus Eigenmann & Eigenmann,
and a species of Syngnathus were never attacked
or threatened, while juveniles of Sparisoma,
equally common on the grass flats, were
vigorously attacked and snapped at. At no time
did they return the fight.
Behavior before a mirror : A pocket
mirror was placed in front of the tube occupied
by a male pike blenny. The type of response was
controlled by the intervening distance and the
rapidity with which the mirror was advanced. At
10 inches interest was exhibited. At about six
inches, interest gave way to tbreat. Failure to
remove the mirror at this point did not result
in attack. Approach to a point somewhat less
than the body length of the blenny resulted in
attack. Slow approaches were successful in a
closer placement of the mirror. A fast approach
alarmed the blenny and resulted in immediate
attack responses. Attack on the mirror image was
violent and since the blenny was evidently
neither victorious nor defeated the attack was
repeatqd many times. Fig. 11, shows the initial
attack of a sequence in its early phase, a
momentary pause before a second attack. The
blenny which is in the middle of combat (in this
case between repeats) is much darker in
dorsal-fin and head coloration compared to the
saine fish at the start of combat. In combats
between two blennies the issue was decided in
every instance during the initial attack and
repeated attacks did not occur.
Proximity of ubes and behavior : Two
occupied tubes were placed in the same section
of the tank, both occupied by males of
Chaenopsis. Again, threat was exhibited at a
distance of about six inches. If the tubes are
left in this position, threat display usually
subsides but may be resumed if one of the
blennies moves suddenly. Gradually the two
appear to accept the reduction in territory size
and threat behavior ceases. Placement of the
tubes at a point where the two blennies may
easily reach each other results in immediate
combat. In one instance the defeated blenny
retreated so rapidly into the tube (Loimia) that
the side was broken out, whereby the vanquished
fish escaped.
Obviously the pike blenny is a strongly
territorial fish but we can report nothing on
its territory size in nature. Efforts to observe
pike blennies in the vicinity of Miami where the
study material was obtained have not been
successful. The concentration of individuals
would appear to be very low in the region.
Similarly, at Soldier Key where one specimen was
collected and a second observed (see above), a
large poison station yielded a variety and
abundance of small bottom fishes but no pike
blennies.
Threat and attack may be elicited by
extraneous objects such as a pencil or finger.
Attack is not repeated on such objects and after
several trials no response will be given for one
or several days. The initial attack, however,
does not lack in vigor and one blenny was
completely raised from the water before
loosening its grip.
Spurious attack.-While photographing
the pike blennies, attacks were stimulated
repeatedly for an hour or more at a time without
diminution of the response though it became more
difficult to prod one blenny into the second's
territory. The intrinsic factors that control
the various responses are apparently maintained
at a high level in the male pike blenny and
accumulate if no need for their use is
forthcoming. A pike blenny kept alone or far
removed from another pike blenny may vary its
behavior suddenly. Thus its head and dorsal fin
will darken periodically and then fade, without
any external stimulus. Attack usually will
follow several such changes. Since no fish or
invertebrate is near, the attack is directed
against some nearby object such as a small stone
or merely a nearby point in the sand.
Feeding behavior : Feeding was
observed and recorded when the biennies were
free in a 15gallon aquarium and when they were
in both horizontal and vertical tubes. Any
drifting or swimming object elicited interest.
At such times the body, if relatively straight
at the time, was now curled and the dorsal
partly erected (Plate 1, Fig. 2). A quarter-inch
grass shrimp (Tozeuma) was caught by a sudden
strike from the semi-coiled position. Shrimp
were caught from the side, vigorously clamped
and then shifted longitudinally in the mouth,
and after several bites swallowed entire. If the
grip was not satisfactory the shrimp was spit
forward and a fresh grip made. The dorsal flash
spot was not exposed, nor were the
branchiostegal membranes. Food items never
elicit threat display. On one occasion strikes
were directed against three small shrimp which
swam by above the bottom, and a fourth shrimp
which rested nearby on the sand was stalked and
caught. The pike blenny will readily leave its
tube in catching food. A small mojarra
(Eucinostomus) about 12 mm. long was caught and
eaten and a small piece of ground fish placed
nearby was also eaten.
