TAIL BEATS/SECOND 



Figure 3, --Swimming speeds and their relation to 

 tail-beat frequencies for yellowfin, skipjack, 

 and bonito. 



showed that these pelagic schooling fish have definite court- 

 ship rituals which include temporary pairing of the sexes, 

 aggression between males, and adjacent release of eggs and 

 milt. Bonito of both sexes have the same external appearance. 

 Members of one sex identify members of the other by behavi- 

 oral differences between the sexes rather than by physical 

 dilferences in coloration or shape. During bouts of aggressive 



behavior, males were observed to display a transient verti- 

 cally barred coloration pattern, apparently as a threat to other 

 males. Similar color changes are known to occur in skipjack 

 tuna, little tunny, and Pacific bonito while they are feeding 

 (fig. 4) and these color changes also may serve as a threat to 

 nearby fish. 



TYPICAL 



TRANSIENT 



V 



Figure 4. --Transient coloration patterns (right) observed in 

 (top) skipjack, (middle) little tunny, and (bottom) Pacific 

 bonito at feeding time. Typical patterns shown at left. 



