partitus . However, limitations of resolution in the underwater camera used for 

 field observations precluded analyses as detailed as those obtained during the 

 laboratory section of the work. Therefore, the two parts of the study were not 

 strictly comparable. 



Many damselfish are territorial, and the bicolor, like several other 

 closely related species, defends a territory which it infrequently leaves. In 

 the field, several or many such territories may be found in close proximity, 

 forming colonies on suitable substrate. Reproduction usually occurs within 

 colonies, which consist of both males and females. Colony members frequently 

 interact with each other close to territory borders. In small colonies, all 

 colony members may interact with one another, whereas in very large colonies 

 many individuals rarely come into contact. Small colonies are, therefore, 

 particularly useful for studies on intracolony social relationships. 



The aims of the present study were: (a) to examine in detail the aggressive 

 social interactions of small colonies of the bicolor damselfish in the field 

 and (b) to compare the dominance system of these colonies with hierarchies 

 found in the laboratory (Myrberg, 1972aJ. 



METHODS 



The study was conducted from October 9-16, 1980, from the NOAA underwater 

 facility, HYDROLAB, situated in 50 feet of water off the north coast of St. 

 Croix in the U.S. Virgin Islands. 



Seven small damselfish colonies, each confined to a patch of coral rubble 

 and separated from each other by clear areas of sand, were selected. The 

 colonies were small enough to permit interactions between all colony members. 

 Aggressive social interactions ("chases") were recorded between all individuals 

 in each colony, where both the giver and receiver of each "chase" were noted. 

 A chase is defined as a rapid swim towards a fish that is moving away or that 

 starts to move away from the chaser (Myrberg, 1972bJ. 



Each colony contained six to eight individuals, most of which were 

 distinguishable on the basis of size. However, very small fish ("tinies") were 

 difficult to identify individually. Consequently, in the colonies containing 

 more than one "tiny," i.e., in colonies larger than six fish, the number of 

 interactions per tiny was determined by dividing the sum of chases given or 

 received by all tinies of a particular colony by the number of tinies in that 

 colony. Therefore, in each colony larger than six individuals, the rank (see 

 below) of six consisted of an average interaction rate per tiny. 



Data were taken during both the morning and afternoon over a period of 

 3-6 days and until at least 65 interactions had been noted for each colony 

 (average observation time per colony = 131 minutes; range = 85-240 minutes). 

 Since colonies were monitored for varying lengths of time, the observations 

 were standardized to give the number of chases per 100 minutes per colony so 

 that the colonies could be compared directly. 



Matrices were constructed for the chase data from each colony by assigning 

 dominance ranks to every colony member. For example, rank 1 chased each other 



130 



