mise à jour du
15 janvier 2004
Proceedings of the zoogical
society of London
1959; 44; 77-84
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. [...]
pike blenny
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.