ESCAPE RESPONSE IN A POMACENTRID REEF FISH 



Peter H. Hartline 



Ann C. Hartline 



Alina M. Szmant 

 Arthur 0. Flechsig 

 Scripps Institution of Oceanography 



ABSTRACT 



We have quantitatively studied the visual cues which evoke 

 escape responses in a small pomacentrid fish which schools 

 around particular landmarks in coral reefs. Models of 

 different shapes, sizes, and colors were used to explore 

 characteristics of the response-triggering stimuli. Con- 

 trast, or dark color, of the model relative to the back- 

 ground and size are important in triggering the response. 

 The proximity of the models at the time of response was 

 independent of model speed. Our observations of natural 

 behavior suggest that the fish may recognize more complex 

 characteristics of intruding fish (such as color pattern, 

 details of shape, and sounds) in evaluating escape 

 evoking stimuli. 



OBJECTIVES 



Escape responses are among the overt ways in which one species may 

 affect the behavior of another. They have been studied in many land 

 vertebrates in the context of trigger features, social communication, 

 and fixed action patterns. We wanted to study escape responses in 

 the coral reef environment, where the density of species and individ- 

 uals is high. The species Chromis cyanea was selected because of its 

 schooling tendency, and its characteristic escape response. When 

 startled, the fish in a school turn toward their home landmark 

 (e.g. a coral head) and swim toward it as a group. We wished to film 

 the responses for later careful analysis, in which quantitative 

 estimates of the important parameters which control the responses 

 could be made. 



We designed experiments to assess the role of model shape and size, 

 speed of approach, and model color and pattern, in evoking escape. 

 We wanted to determine the extent to which auditory or vibratory 

 components of stimuli were important in generating responses. 

 Finally, we wanted to make observations of natural behavior of the 

 Chromis and relate these observations to our experimental results. 



EQUIPMENT AND PROCEDURES 



Flat plastic models were cut into circular, square, or elliptical 

 shape, and were pulled through the water near a coral head which was 

 the home of a school of blue chromis ( Chromis cyanea ) . The behavior 



VI-201 



