FISHERY BULLETIN: VOL. 70, NO. 3 



(120: 74-145 mm), and M. berndti (169: 136- 

 270 mm) , all emerge at the same time. All move 

 right up into the water column, although M. 

 ynultiradiaUis, the smallest of the three, stays 

 closer to the reef than the other two. Almost 

 immediately, many individuals of M. argyromits 

 and M. berndti move offshore in mass. That 

 fishes of this genus migrate offshore at night 

 was noted by Gosline (1965), and their noctur- 

 nal plankton-feeding habits have been estab- 

 lished (Hobson, in preparation). 



At about the same time, bigeyes, Priacanthiis 

 cruentatus (173: 115-255 mm), rise from the 

 rock and coral crevices that had sheltered them 

 in daylight and, forming schools high above the 

 reef, most of them swim offshore. The offshore 

 migration at night by P. cruentatus was noted by 

 GosHne (1965), and the feeding habits of this 

 fish were studied (Hobson, in preparation). 



At about the same time that fishes are reoc- 

 cupying the water column, many other nocturnal 



fishes that are active only close to the substrate 

 begin to be seen for the first time. These are 

 mostly small species under about 200 mm long, 

 and all are predators. Included are a number 

 of squirrelfishes of the genus Holocentriis, in- 

 cluding H. xantherythnis (106: 88-123 mm), 

 H. diadema (109: 85-127 mm) , H. kicteoguttatiis 

 (88: 52-104 mm), H. tiere (141: 67-235 mm), 

 and Holotmchys lima (91: 70-113 mm); also 

 the scorpionfishes Dendrochinis brachypteriis 

 (99: 80-118 mm), Pterois sphex (83: 58-121 

 mm), and Scorpaena coniorta (46: 26-67 mm), 

 and the brotulid Brotula multibarbata (169: 73- 

 250 mm) . The nocturnal feeding habits of these 

 fishes were studied (Hobson, in preparation). 



To the human eye, it is nighttime on the reef 

 at about 50 min after sunset, although the last 

 vestige of daylight is still visible on the water's 

 surface overhead. By this time the nocturnal 

 situation prevails and will continue to do so until 

 morning (Figure 6). 



Figure 6. — Nightime on a coral reef in Kona, Hawaii. The fishes swimming- above the 

 reef are squirrelfish, Myripriatis spp. At lower right center a single surgeonfish, Zebra- 

 8oma flavenscens, is nestled among the coral; the horizontal white bar on its side is, 

 in adults, a feature of its nocturnal coloration. 



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