Introduction

Early ethologists, especially Oskar Heinroth and Konrad Lorenz in Germany and Julian Huxley in England, recognized that many animals have a number of distinct action patterns used in social interactions.   These action patterns, sometimes called displays, often seem bizarre and mechanical to our eyes.

Because these displays are often repeated in almost the same way, performance after performance, and because different individuals of the same species often perform the displays almost the same way, they have often been called fixed action patterns.   In some cases they are fixed in another way also:   they are not learned from other members of the species; instead each individual develops these displays without having observed them previously.

Careful study has revealed that these action patterns do vary, sometimes considerably.   Nevertheless, they are often easily recognizable because the animals rarely perform any action intermediate between different displays.   Because they are not "fixed", perhaps the best term is simply action pattern.

In this exercise, we investigate the displays of paradise fish (Macropodus opercularis).   Once you learn to recognize their displays, try to observe how variable and how discrete they are.

In addition, we examine a general feature of behavior -- habituation.   Habituation is a decrease in the intensity of response to a constant or repeated stimulus -- a decrease not explained by muscular fatigue (muscles no longer respond after repeated stimulation) or sensory adaptation (sensory neurons no longer respond after repeated stimulation).   Habituation is a result of changes in the central nervous system, not in sensory or muscle cells.

To study habituation, we must measure the intensity of responses to a stimulus, for example a mirror image or a picture.   Some measures of response intensity are

• the rate of response (number of actions per minute)
• the latency of response (time between the presentation of a stimulus and the first response)
• the duration of response (for instance, seconds of response per minute of observation).  

We use some of these measures in our investigation of habituation.

Procedures

Your fish have been visually isolated for about two weeks in individual tanks.   Organize yourselves in groups of two.   Each pair of observers will have one fish.

Observe the typical resting behavior of the fish.   Note the general body postures, the color patterns, the normal rates of gill movement, the normal rate of rising to the surface for air (these fish belong to an Asian family that can breathe air), and the rate of pectoral fin fanning.   Time these actions with a stopwatch.

Study the reaction to mirrors.   Place a mirror at one end of the tank so that it covers the entire end.   Observe the changes in behavior from the resting state.   Observe the fish for 15 minutes.   Measure the intensity of responses each minute (see above).

Is there a tendency to habituate to the mirror?   Are the displays performed the same way each time?   How much do they vary from performance to performance?   Can you recognize more and less intense versions of each display?   How could you rule out muscular fatigue or sensory adaptation as explanations for the decrease in responses?

Observe the behavior of two fish together.   Combine with another group to make a group of four.   Each team of two should keep track of the behavior of one of the two fish.   Put two fish together (remember which ones they are so you can compare their behavior to that in the mirror test).   Typically they approach and circle slowly around each other.   After this approach and circle, a complete aggressive encounter usually includes these behavior patterns:   (a) frontal display; (b) lateral displays; (c) lateral attack; (d) head ram; and (f) jaw lock.   The encounter sometimes does not proceed all the way to attack and fighting.

Are the displays performed in a fixed sequence?   Do less intense displays tend to precede more intense ones?   What happens if one fish becomes subordinate and the other dominant?

Descriptions of Displays

Frontal display

gill covers (opercula) erected, presenting a larger frontal profile to the opponent.

Lateral display

four major components include antiparallel head-to-tail orientation, expansion of the dorsal and caudal fins, S-shaping of the body, and quivering or vibration along with rapid beating of the pectoral fins.

Lateral attack

a glancing attack directed at the flank or side, usually at the base of the opponent's tail; normally seen at the end of the vibration that terminates lateral display.

Frontal attack

biting directed at the head, mouth or operculum of the opponent.

Head ram

self-explanatory.

Jaw lock

one male grabs his opponent's lower jaw and a wrestling contest ensues; often preceded by head ramming.

Subordinate behavior

fins folded, body axis at 45 degrees to horizontal (head upward), color change to a lighter shade, little motion except when chased.

Questions

Why do these fish display to each other rather than attack without displaying?

Why do you think they respond differently to mirrors and live opponents?

How variable are these displays?   How does variation in the performances of one fish compare with variation between different individuals?   Are sequences of displays more or less variable than the displays themselves?

How many distinct action patterns have you recognized in interactions of two male paradise fish?   Why are there not more, or fewer?

Why is it adaptive for an animal to habituate to a constant or repeated stimulus?

References

Bronstein, P.M.   1994.   On the predictability, sensitization and habituation of aggression in male Bettas (Betta splendens).   J. Comp. Psych. 108(1): 45-57.

Francis, R. C.   1983.   Experiential effects on agonistic behavior in the paradise fish, Macropodus opercularis.   Behaviour 85:   292-313.

Francis, R. C.   1984.   The effects of bidirectional selection for social dominance on agonistic behavior and sex ratios in the paradise fish (Macropodus opercularis).   Behaviour 90:   25-45.

Francis, R. C.   1987.   The interaction of genotype and experience in the dominance success of paradise fish (Macropodus opercularis).   Biology of Behaviour 12:   1-11.

Miklosi, A., J. Haller, and V. Csanyi.   Learning about the opponent during aggressive encounters in paradise fish (Macropodus opercularis L.): When it takes place?   Behavioural Processes 40:   97-105.

Rasa, A. O.   1969.   Territoriality and the establishment of dominance by means of visual cues in Pomacentrus jenkensi .   Zeitschrift fŸr Tierpsychologie 26:   825-845.   (shelved with the journal Ethology in the Zoology Library)

Thompson, T. I.   1963.   Visual reinforcement in Siamese fighting fish.   Science 141:   55-57.