FISHERY BULLETIN: VOL. 72, NO. 4 



General Remarks on Silversides 



It is widely recognized that silversides prey 

 largely on zooplankton. Hiatt and Strasburg 

 (1960) found mostly zooplankton in three species 

 in the Marshall Islands, as did Randall (1967) in 

 two species from the West Indies. Each report 

 listed shrimp larvae and copepods among the 

 major food items, but neither mentioned noctur- 

 nal habits. At Majuro Atoll, Marshall Islands, 

 Pranesus pinguis is inactive in schools along 

 lagoon beaches during the day, and then migrates 

 offshore into the lagoon at nightfall, where it dis- 

 perses and feeds on zooplankton in the surface 

 waters (Hobson and Chess, 1973). The closely re- 

 lated P. insularum does not move so far from 

 shore at night in Kona, presumably because its 

 feeding grounds are over the nearshore reefs. 



Order Beryciformes 



Family Holocentridae: squirrelfishes 



The squirrelfishes compose one of the more 

 prominent groups of fishes on Hawaiian reefs. The 

 species fall into two major categories: those in one 

 group include members of the genus Holocentrus, 

 which are known by the generic Hawaiian name 

 ala 'ihi, and one species of the genus Ho lotrachys; 

 those in the second group include species of the 

 genus Myripristis, which are known by the 

 generic Hawaiian name 'u'u, or perhaps more 

 often today by the Japanese equivalent menpachi. 



Holocentrus sammara (Forskal) 



This solitary fish is numerous in coral-rich sur- 

 roundings at depths between 4 and 20 m. It is a 

 relatively large species — up to 300 mm long (Gos- 

 line and Brock, 1960) — and characteristically hov- 

 ers in visible locations at the openings of reef caves 

 during the day. During evening twilight it moves 

 away from its daytime shelter-sites and through- 

 out the night ranges over the nearby areas of the 

 reef, staying close to the sea floor. During morning 

 twilight it gradually moves closer to cover and by 

 sunrise has resumed its daytime mode of be- 

 havior. After dark the coloration of this fish differs 

 from its coloration in daylight (Figure 11a andb). 



Twenty-one specimens (162: 128-202 mm) were 

 collected during day and night for food-habit 

 study. All 13 that were speared as they swam in 

 exposed positions on the reef during the last hours 



of darkness, before daybreak, and during morning 

 twilight contained prey in varying stages of diges- 

 tion. In comparison, of seven speared as they 

 hovered close among coral shelter during the after- 

 noon, four were empty, two contained only well- 

 digested fragments, and one contained an appar- 

 ently recently ingested crab. Finally, one that was 

 speared in the open 4 h after nightfall was full of 

 prey, most of it fresh. Items in the 17 specimens 

 containing identifiable material are listed in 

 Table 10. 



CONCLUSION. — Holocentrus sammara is a 

 nocturnal predator that feeds mostly on benthic 

 crustaceans, especially xanthid crabs and carid- 

 ean shrimps, but some feed diurnally. 



Holocentrus spinifera (Forskal) 



This is the largest squirrelfish on Kona reefs, 

 and of those considered in this report it is also the 

 least numerous. A solitary species during both day 

 and night, it is secretive within reef crevices in 

 daylight, but ranges out and forages close to the 

 reef after dark. In daylight, the body of this fish is 

 a plain rosy-red, and its dorsal fin is yellow; in 

 darkness, however, a small but prominent white 

 spot appears on each side of its body, just behind 

 its dorsal fin. Because this large fish is not numer- 

 ous, I came to recognize certain individuals and 

 found that after nocturnal forays on the reef each 

 tended to return each morning to its particular 

 shelter spot. 



Six specimens (213: 68-350 mm) were speared 

 during day and night for study of food habits. The 

 one that was taken during midday contained a 

 large caridean shrimp, Saron jnarmoratus (about 

 40 mm), that was extensively damaged by diges- 

 tion and could have been taken during the previ- 

 ous night. A second, taken as it emerged from 

 cover at nightfall, was the only one taken with an 

 empty gut. Of the other four, all of which con- 

 tained relatively fresh prey, three were collected 

 as they swam in the open at night, more than 3 h 

 after sunset, and the fourth was collected under a 

 ledge during morning twilight. 



All five specimens containing food had fed on 

 crustaceans exclusively. Three had taken carid- 

 ean shrimps (mean percent of diet volume: 34; 

 ranking index: 20.4), three had taken xanthid 

 crabs (mean percent of diet volume: 31; ranking 

 index: 18.6), and one had taken a scyllarid lobster 

 (mean percent of diet volume: 11; ranking index: 



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