Ethological observations on the blennioid fishes Hypsoblennius hentz (Le Sueur) and Chasmodes saburrae (Jordan and Gilbert)

ABSTRACT

Two species of blennioid fishes Hypsoblennius hentz (Le Sueur) and Chasmodes saburrae (Jordan and Gilbert), were contained in aquaria and observed from 10 February 1966 to 31 March 1966. Resting, locomotion, aggressive, defensive, feeding, territorial and spawning behavior were observed and described. Spawning was observed only in H. hentz . Parental care was restricted to egg guarding by the male. The fry hatched after a period of 8 to 10 days. H. hentz exhibited more complex behavioral patterns than C. saburrae and is assumed to have reached a higher evolutionary level. Blennies are considered to have an excellent potential for ethological investigations.

INTRODUCTION

Blennies are small, shallow water coastal fishes with an extensive distribution. A great deal of speciation has occurred in the evolutionary history of the family Blenniidae. Since these fishes are for the most part restricted to coastal environs, this speciation has probably resulted from coastal discontinuities of past geological ages.

Blennies are good subjects for ethological studies because of the following factors. (1) They are readily available from temperate and tropical areas and their shallow water habitat allows observation in natural surroundings as well as easy procurement. (2) Blennies are hardy fish and adapt well to small aquaria and reduced salinities. (3) Sexual dimorphism and a repertoire of behavior patterns are present in blennies.

Behavioral investigations on blennies are sparse and mostly restricted to accounts of nests, eggs, and developmental stages (Ford, 1922; Hildebrand and Cable, 1938; LeBour, 1927; Shultz and DeLacy, 1932). Robins, Phillips and Phillips (1959) published extensive behavioral observations on pike blenny, Chaenopsis ocellata. Dr. John S. Stephens of Occidental College and Dr. George Losey of Scripps are currently working on ecological aspects of micro separation and comparative breeding behavior, respectively, of Northeastern Pacific species of Hypsoblennius. Little is known of the behavior of Atlantic blennies, and to my knowledge, nothing is known of behavior in the Gulf of Mexico species. Blennies provide an excellent opportunity to contribute to ethological knowledge of fishes.

Hypsoblennius hentz and Chasmodes saburrae are the common blennies of the Tampa Bay, [Florida], area. Both species range over most of Florida, but H. hentz occurs from New Jersey to Yucatan (Hubbs, 1939) while C. saburrae is replaced by its congener, C. bosquianus, at about Matansa Inlet on the Atlantic coast and at about Pensacola on the Gulf coast. A small area of sympatry occurs on the Gulf coast between Florida and Louisiana.

METHODS AND MATERIALS

Blennies were selected as the subject of my project in animal behavior because I was acquainted with them in the field and knew they adapted well to aquaria. A bait shrimper, Tom Stokell, was able to supply me with both species of blennies and I soon had enough fish for the duration of the study.

C. saburrae were obtained from the shallow grass flats of upper Tampa Bay and H. hentz were taken from irregular bottom in lower Tampa Bay. The fish were transported to the Florida Board of Conservation Marine Laboratory in St. Petersburg, the site of this study. Three aquaria were set up to contain the blennies. A large 20 gallon aquarium was used as a holding tank to assure a continuous supply of fish and two 10 gallon aquaria were set up as experimental tanks with a gravel substrate, false turtle grass, Thalassia, and a variety of shells and coral pieces.

Observations spanned the period from 10 February 1966 to 5 April 1966. A total of about 45 to 50 hours were spent in watching and working with the fish. Most observation periods were limited to less than one hour, but several periods of two to four hours contributed to the total observation time. The following program summarizes the manipulation of aquarium contents during the course of the project. The contents of the 20 gallon tank were not significantly changed.

10 February 1966: Eighteen C. saburrae were obtained and placed in the 20 gallon aquarium. Observations on aggregating and feeding behavior followed.

18 February 1966: Twenty H. hentz were been obtained and placed in the holding tank.

22 February 1966: One male and one female C. saburrae were placed in a 10 gallon aquarium under conditions that simulated the natural environment.

24 February 1966: One male and one female H. hentz were placed into a second 10 gallon aquarium under conditions that simulated the natural environment.

28 February 1966: A second male was placed into each aquarium to supplement the original pair of each species.

U: The spawning of H. hentz was observed.

2 March 1966: C. saburrae were taken from the 10 gallon aquarium and returned to the holding tank. Two male and two female H. hentz were placed in this aquarium in hopes that they would also spawn.

3 March 1966: The new or second tank of H. hentz also spawned.

7 March to 13 March 1966: Intermittent observations.

14 March 1966: Fry were found in the second tank of H. hentz. The fish were removed from the first tank of H. hentz with the exception of the dominant male. Two new females and one new male were introduced into the tank. H. hentz were also removed from the second tank and replaced with C. saburrae; two males and two females. The first 10 gallon aquarium now contained a new compliment of H. hentz and the second 10 gallon aquarium now contained only C. saburrae as it was originally intended.

15 March to 21 March 1966: Intermittent observations.

22 March 1966: A pair, male and female, of C. saburrae were placed in the first aquarium with the group of H. hentz, and a pair of H. hentz were placed in the second aquarium with the group of C. saburrae.

27 March to 31 March 1966: A fungus infection attacked the fish in the small tanks and then moved to the large tank. Most of the blennies were killed and the observations terminated.

H. hentz and C. saburrae differ both morphologically and ethologically. Morphology is important to behavioral studies since structure closely reflects function. Taxonomic descriptions of these fishes are available in the literature (Hubbs, 1939; Springer, 1959) and will not be repeated here.

The general form of H. hentz is illustrated in Figure I, as are the characters of sexual dimorphism. The males have a much larger orbital tentacle and attain greater size than females. Also, the first two anal spines of the male are modified into broad leaf-like structures and the anterior portion of the dorsal fin has a bright blue spot rather than a diffuse white area as in the female.

Figure II illustrates the general form of C. saburrae and the characters of sexual dimorphism. Only the male is figured since the female differs from the male only in the absence of the depicted characters. The males attain greater size than the females, possess a bright blue spot between the first two dorsal fin spines and have the first two anal spines modified into bulbous, finely striated structures. The genital area in the females of both species is enlarged into almost a papillate structure.

RESULTS

Although most behavior patterns reported below were observed repeatedly, lack of time prevented a quantitative analysis of behavior. Observations were not extensive enough to allow more than subjective estimates of display intensity levels. Results for both species are listed together under each general category of behavior to facilitate comparison.

General aquarium "attitude":

It is anthropomorphic to use the term "attitude" or "personality" in describing the actions of the fish, but I shall do so here to convey the general impression on the habits of each species.

H. hentz are bold, curious little fish. They dart rapidly about the aquarium and perch atop shells while actively surveying their environment. They are openly aggressive and chase each other about the aquarium. A finger pressed against the glass will entice them to leave the shelter of their shell and peck eagerly at the glass.

C. saburrae are shy little fish. They seldom leave the security of shelter, and when they do venture forth, it is only to effect an immediate return or travel to another secure location.

Resting behavior:

H. hentz is a robust little fish. Its pedestal shaped pelvic fins are thoracic and are used to support the anterior portion of the body well above the substrate when the animal is motionless. The posterior portion of the body is supported by the anal fin in tripod fashion. The dorsal fin is always erect when the fish is motionless in the open, but it may be erect or depressed when the fish is sheltered. H. hentz often frequents sheltered areas so small that it must curl its body to accodomodiate to them. The fish always enters the shelter head first and turns around to face outward.

C. saburrae is rarely motionless in the open. It is more slender than H. hentz and often enters crevices that require it to lie on its side. Resting can occur in either an upright posture as exhibited by H. hentz or in a lateral orientation. No preference for either position was observed, but contact with a solid object was always sought. C. saburrae always oriented in its shelter with the head facing outward.

Locomotion:

H. hentz exhibited three forms of locomotion; swimming, hopping, and creeping. The pectoral fins are t he main organs of movement control and the caudal fin provides the power of movement. Swimming is accomplished by rapid beats of the caudal fin which sends the fish upward and forward. Continuous swimming is not observed and complete trips over the length of the aquarium are rare. Hopping consists of short bouncy movements along the substrate. A distance of 3 to 6 centimeters was covered with each hop and the fish rose only about 2 centimeters off the bottom during the hop. Several hops usually occurred in sequence with a brief pause between each hop. Creeping usually occurred at the edge of the glass or in the shelter. It consists of ambulatory movements of the pelvic fin and pushing against shelter or bottom with the caudal fin. This resulted in slow movement within a small area and allowed the fish to orient in a micro-environment.

C. saburrae exhibited swimming and slithering. The caudal fin provided the power and the pectoral fins the control for both movements. C. saburrae is a great deal more slender in body than H. hentz and its movements undulatory rather than the jerky, back and forth motion. [ of H. hentz ] The fish moved about the shells and coral most frequently with a slithering movement. The undulating body came in frequent contact with the shells and gravel and produced an eel-like effect in the fish's movements. The pelvic fins were used in positioning, but C. saburrae was not observed to use them in pulling itself along the bottom.

Aggressive behavior:

Males of H. hentz displayed a deal of aggressive behavior. Other male H. hentz were the most frequent objects of aggressive behavior, but females and other species were also attacked. The low intensity threat display appeared to be an erect posture facing the intruder, erect dorsal fin and orbital tentacles, and possibly a darkening of the epidermis. When attack was near the male would open his mouth and then charge the intruder and attempt to bite. A short chase usually followed when the intruder fled. These encounters occurred rapidly and it was difficult to discern exactly what happened. Male H. hentz were often missing orbital tentacles and I believe these were lost during encounters with other males. The males were continually on guard under crowded conditions. Females were not observed to display aggressive behavior.

C. saburrae did not display aggressive behavior in the aquarium. Several males would often occupy the same shell.

Defense behavior:

Defensive behavior in H. hentz includes three behavior patters that usually occur in sequence; concealment, avoidance, and threat with attack. H. hentz seeks to conceal itself upon initial disturbance. If a shell or crevice is not available it flattens against and tries to burrow under any nearby solid object. If disturbance persists, the blenny no longer suppresses movement and shows active avoidance behavior. Avoidance begins with movements to secure greater concealment, progresses into flight to another shelter, and terminates in a panicky flight into the aquarium wall. H. hentz does not show threat and attack in a defensive situation until the possibility of avoidance has been nullified.

The defensive threat posture differs from the aggressive threat in two manners. The dorsal fin is erected as in aggressive threats, but the body is curved as if in a shell and the mouth is held open. The curved body directs the dorsal spines towards the stimulus, and coupled with the erect dorsal fin, increases the apparent body size. The open mouth corresponds with the highest intensity level of aggressive display prior to actual attack. Defensive attack does not occur until the fish is approached and touched. The bite of attack is similar to feeding action. The bite is effected in a bulldog manner with a strong, tenacious grip and a rapid shaking or jerking of the head. The blenny immediately seeks concealment when the disturbing stimulus is removed. Both males and females displayed the same defensive behavior.

C. saburrae displays concealment and avoidance to a greater degree than H. hentz. It also exhibits the same defensive threat behavior, but at apparently a lower level of intensity. C. saburrae did not engage in panicky flight from the disturbing stimulus. It continued rapid avoidance movement from shelter to shelter until capture.

Feeding behavior:

The blennies were fed once a day and occasionally every other day Food consisted of small pieces of cut shrimp and fish dropped into the aquarium.

H. hentz would gather at the front of the aquarium during feeding. When the food was dropped into the aquarium, one or two of the larger males in the holding tank would dart upward, seize the food, and take it to the bottom. They were then the focus of attention and as they shook loose a morsel of shrimp the other H. hentz would move in, grab a mouthful, and quickly swim away. This interaction continued until the food was consumed. The dominant male in the 10 gallon aquarium was always first to grab the food, but the other males and females quickly moved in and took their share.

C. saburrae were more timid in their feeding behavior than H. hentz. They remained in their shelter for several minutes after the food was introduced and then rapidly swam to the food, took a quick bite, and returned to their shelter. Even if the attack on the food was unsuccessful, the fish returned to its shelter before making another attempt to secure food. When C. saburrae and H. hentz were together, C. saburrae obtained scraps that drifted near them as H. hentz fought over the food. If the food particle was too large to ingest at the site, C. saburrae would return to its shelter before tearing it apart.

Territorial behavior:

H. hentz, particularly males, vigorously defended an area of about 4 - 6 centimeters around their body. This area varied as the fish changed positions in the aquarium. There was a marked tendency for the larger males to remain in the vicinity of a particular shell, corner, or coral piece. Smaller males and females were easily chased away from an isolated area they frequented as well as the established area of a large male. A large male in the 10 gallon aquarium that always housed H. hentz was always dominant over all the other individuals in the aquarium, both new and old residents. He had a particular area he frequented, but often roamed the aquarium and chased other males from their shelters. The displaced male would find another shelter and then return to his original shelter when the dominant male left. He [ the dominant male ] always returned to his corner after a short period occupation. The dominant male exhibited strict territorial behavior only during, and for a day or so after, spawning occurred in his territory. Territorial behavior and individual distance are difficult to separate in H. Hentz and it is probable that defense of individual distance merges into territory defense at certain times in the life cycle.

C. saburrae did not show strong territorial behavior. They could be easily displaced by other fish and would often aggregate in groups of two and three under the same shell. This aggregative behavior did not appear to be normal for the fishes were always solitary when enough shelters were available.

Spawning behavior:

H. hentz was the only species that spawned in the aquarium and spawning was only observed once, although it occurred several times. A summary of the notes taken during spawning is presented to describe this activity since generalizations developed after repeated observations cannot be provided.

Spawning was observed in the 10 gallon aquarium containing two males and one female. Male #1 was larger than, and dominant over, male #2. Spawning took place 1 March 1966 in a far corner of the aquarium close to the wall of the building. A depression had been excavated in the gravel bottom of the corner. Both male and female blennies were observed to excavate these depressions, always near a sold object, with quick movements of the tail and body. The female rapidly moved her tail and posterior portion of her body back and forth in a lateral plane as her pectoral fins rapidly beat up and down. Her pelvic fins and abdomen were tightly pressed against the glass and she moved slowly up and down the glass wall in the corner of the aquarium. Her genital; papilla was reddened and slightly swollen. Eggs were placed on, and adhered to, the glass either singly or in small groups.

Male #2 moved very near the female and assumed the same method of movement and position on the glass. He was sometimes above, sometimes below, and sometimes beside the female during their simultaneous "wiggle walk" along the wall. The dorsal fin of both male and female were erected during all activity.

The first three dorsal spines and the membrane between them are white in the female and gives the anterior portion of the fin a flag-like appearance. During and just before spawning the spot between the first two dorsal spines becomes a well-defined, intense white. The anterior portion of the dorsal fin in the male remained dark except for the spot between the first two dorsal spines which was a pronounced electric blue. Five very pronounced white lateral line spots were always present on the female and variably present on the male.

Spawning activity between male #2 and the female was apparently broken by male #1. He (male #1) attacked the spawning pair and drove them from the corner. Male #1 then "wiggle walked" over the attached eggs at irregular, frequent intervals. The female attempted to return and resume spawning. Male #1 allowed her to make a few "wiggle walks" and then chased her away. Male #2 attempted to visit the area just covered by the female and was immediately chased away by male #1. Male #1 makes a few "wiggle walks" and remains in an alert posture.

Male #2 moves to the opposite corner of the aquarium and assumes a resting position. The female digs a nest in another corner of the aquarium and "wiggle walks" on the glass. Eggs are not laid down and neither male shows interest in her activity. Random movements of both the female and male #2 occur. The female enters a small Strombus shell and then digs a depression in front of the shell. Male #2 observes the activity and chases her away from the area. Male #2 then vigorously tries to enter the shell, however it is too small to accommodate him. Male #2 expends much time and effort trying to enter the shell, without success.

The female approached the shell three times and was repulsed by male #2 each time. I attracted male #2 to the front of the aquarium several times by moving my finger against the glass. Each time I removed my finger he returned to the shell and resumed his futile attempts to enter. Although male #2 was easily enticed to the glass, male #1 never left his corner (and eggs).

Spawning also occurred in the larger holding tank. Eggs were adhered to the narrow glass wall at one end of the aquarium and a male H. hentz guarded an area of about 15 centimeters in front of the eggs. Both of his orbital tentacles were gone and he was consistently in a threat posture. The next day the eggs were no longer guarded and they soon disappeared.

The vigilance of male #1 gradually diminished and after three days he paid no special attention to the eggs. Spawning also took place in the other 10 gallon aquarium, but the act was not observed. The males in this aquarium were not observed to guard the eggs. Three millimeter fry were taken from this aquarium on 14 March 1966. A period of about 10 days elapsed between spawning and hatching.

DISCUSSION

H. hentz and C. saburrae appear to be ecologically separated in the Tampa Bay area. The collections of Springer and Woodburn (1960) and the collection for the present study indicate that C. saburrae occurs primarily on shallow grass flats and H. hentz occurs on deeper irregular bottoms that may or may not have a grass cover. Their behavior also indicates ecological separation. Although both species exhibit strong stereotaxis, H. hentz is less dependent on concealment than C. saburrae. Johnson (1965) discusses ecological separation in several species of Hypsoblennius and notes that pressures of predation and tidal surge are responsible for the development of strong concealment drives in H. jenkinsi.

Feeding in this species ( as in C. saburrae) is characterized by darting out from concealment, feeding, and returning at once. The behavior of H. hentz indicates a greater freedom from predation than is enjoyed by C. saburrae. Also, the behavior patterns of H. hentz are apparently more elaborate than C. saburrae and indicate that H. hentz is the more evolutionary advanced species. Taxonomic knowledge of the group is poor, (the osteology of many genera is unknown), thus behavioral findings and conclusions cannot be correlated with morphological analysis.

Hildebrand and Cable (1939) collected the nests of H. hentz and C. saburrae to obtain material for embryological studies and noted that the male must always guard the nest if the eggs are to escape predators and fungus disease. They also concluded that the male must clean the eggs in some manner. It is possible that the male uses his modified anal spines both to fertilize and clean the eggs. Observations of repeated "wiggle walks" over eggs by the guarding male support this conjecture.

Blennies have excellent potential for ethological studies. Most of the concepts and experiments discussed by Baerends (1957) can be applied to blennies even though they were developed through studies with primarily fresh water fishes. More thorough studies with blennies would probably reveal and define coordinating mechanisms, releasing mechanisms, ritualizations, and various interactions between internal and external factors influencing behavior. Experimental manipulation of sign stimuli and quantitative analysis of behavior patterns would be very useful tools in probing the ethological enigmas of blennioid fishes.

References:

Baerends, G. P., 1957. Behavior: the ethological analysis of fish behavior, p. 229-269. In Margaret E. Brown (ed.) The physiology of fishes, Academic Press Inc., New York

Ford, E., 1922. On the young stages of Blennius ocellaris L., Blennius pholis L., and Blennius gattorugine L.,, Jour. Mar. Biol. Asso., United Kingdom. 12:688-692.

Hildebrand, S. F. and L. E. Cable. 1938. Further notes on the development and life history of some teleosts at Beaufort, N. C. Bull. U. S. Bur. Fish., 48:505-642.

Hubbs, Carl L. 1939. The characters and distribution of the Atlantic coats fishes referred to the genus Hypsoblennius. Pap. Michigan Acad. Sci., Arts, Letters, 24:153-157.

Johnson, Robert K. 1965. A quantitative laboratory study of behavioral differences with applications to the ecology of two sympatric species of Hypsoblennius. (Abstract only), American Zoologist 5:357.

Lebour, Marie V. 1927. The eggs and newly hatched young of common blennies from the Plymouth neighbourhood. Jour. Mar. Biol. Asso., United Kingdom 14:647-650.

Robins, Richard C., Craig Phillips and Fanny Phillips. 1959. Some aspects of the behavior of the blennioid fish Chaenopsis ocellata Poey. Zoologica 44:77-84.

Schultz, Leonard P., and Allan C. DeLacy. 1932. The eggs and nesting habits of the crested blenny, Anoplarcus . Copeia 3:143-147.

Springer, Victor G. 1959. Blennioid fishes of the genus Chasmodes. Texas Jour. Sci. 11:321-334.

Springer, Victor G., and Kenneth D. Woodburn. 1960. An ecological study of fishes of the Tampa Bay area. Prof. Pap. Series 1. Fla. Bd. Cons. Marine Lab. 104 p.