lieprinlfd fmiii COI'KIA, Mlfjl, No. 2, pp. 237-238, .luiii^ l'I 

 l'rinlrd in i\ S. A. 



i àHu^K^ijy 



OBSERVATIONS ON THE SPA^VXI^G OF 

 SURGEONFISHES (ACANTHURIDAE) IN 

 THE SOCIETY ISLANDS.— Few observations 

 hâve becii madc on the actual spawning of marine 

 fishes, and notliing lias becn found in the litera- 

 ture concerning the reproduction of smgeoii- 

 fishes. The author was fortnnate to observe the 

 spawning of tvvo acanthurids in the Society Is- 

 lands, Ctenochaetus striatus (Qnoy and Gaimard) 

 and Zehrnsoma scopas (Cuvier). A detailed ac- 

 coiint of the spawning of a third snrgconfish, 

 Acanthurus triostegus (Linnaeus), in the Tuamotu 

 Archipelago appears in a large paper dcaUng with 

 the biology of this species (Randall, in press, Pa- 

 cific Science). 



Ctenochaetus striatus is the raost common acan- 

 thurid and perhaps the most abundant reef fish 

 of moderate size (it attains about 200 mm. stand- 

 ard length) in the Society Islands. It appears nni- 

 form dark brown underwater; however, if seen 

 at close range, blue longitudinal Unes may be 

 visible on the body and small orange spots on 

 the head. The spawning of this species was ob- 

 served in Tahiti on February 17, 1957. in .\va Iti 

 Pass, a passage about yO fcct deep through tlie 

 barrier reef. The lirst indication of spawning was 



an luiusual concentration of this fish on the 

 northwest side of the pass at about 5 p.m. No 

 further notice was taken until about an hour 

 later when a striking color change of the fish 

 becarae apparent which the author had not seen 

 previously. Instead of appearing iniiform dark 

 brown, the fish wcre pale tan except for about 

 the outer G mm. of the médian fins, the mouth, 

 and middorsal part of the head and nape which 

 were abruptly black (the mid-ventral région of 

 the head was not seen; possibly a black band was 

 présent there too). The fish were aggregated lin- 

 carly along the reef edge at a depth of about 8 

 to 25 feet. None was seen to swira to ihe bottom 

 to fecd. Nearly ail in the group in the deeper 

 Icvcls exhibited the color change, but most of the 

 fish near the surface were entirely dark. Pos- 

 sibly this différence was associated with the prox- 

 iraity of the observer at or near the surface, 

 for the pale, dark-margincd fish altered within 

 a few seconds to dark brown when approached. 

 They appeared to be just as wary of a swimmer 

 at this time as during non-spawning periods. The 

 fish were more active than usual and millcd con- 

 Ntanllv. .\ctual spawning took place when about 



