FISHERY BULLETIN: VOL. 74, NO. 3 



Figure 13.-Blacksmiths, Chromis punctipinnis, aggregated at the edge of a kelp forest, pluck zooplankters from the water column 



during the day. 



of California (Hobson 1968); Hawaii (Swerdloff 

 1970; Hobson 1974). It is also well-known that C. 

 pxucfipinnis is a planktivore. Limbaugh (1955) 

 noted that it feeds on "particulate plankton such 

 as small fish, squid, and crustaceans^ and "may 

 materially affect the amount of plankton entering 

 kelp beds because they eat it as it enters." Quast 

 (1968) listed the principal food of the blacksmith as 

 "minute swimming Crustacea and crustacean eggs 

 and larvae gleaned from open water species of 

 kelp beds and over rocky areas." In taking its tiny 

 prey from the water column in what seems a 

 visually directed action, the blacksmith suddenly 

 thrusts both of its highly protrusible jaws forward, 

 then immediately retracts them, presumably 

 sucking plankters into its rapidly expanding oral 

 cavity. This way of feeding has also been noted 

 among its tropical congeners (Swerdloff 1970; 

 Hobson 1974). 



Aggregations of blacksmiths feeding on plank- 

 ton occurred throughout the water column, with 

 each member of an aggregation acting indepen- 



dently. They aggregated according to size: the 

 discrete aggregations of small juveniles (which 

 first appeared inshore during late summer, when 

 about 15 to 25 mm long) generally were closer to 

 the sea floor than were aggregations of the adults. 

 Blacksmiths fed throughout the day, but the 

 rate at which they ingested prey varied. In the 

 tropical Atlantic, Eupomacentrus partitus, an- 

 other planktivorous pomacentrid, feeds more 

 rapidly with increased light and with increased 

 current (Stevenson 1972). Blacksmiths, too, feed 

 more rapidly in a current than at slack water, 

 presumably (as Stevenson suggested of E. parti- 

 tus) because they receive more plankters. To 

 measure this effect, we counted the characteristic 

 mouth movements of feeding adult blacksmiths, 

 first in a moderate current, and then at slack 

 water. The observations were made during 

 midaf ternoon under a clear sky at a depth of 5 m in 

 10 m of water. The fish were part of an aggrega- 

 tion with members ranging from about 109 to 130 

 mm long (these being the sizes of the two in- 



592 



