FISHERY BULLETIN: VOL. 72, NO. 4 



night after night to caves in the same areas, but 

 not necessarily to the same cave, as has been re- 

 ported for some parrotfishes elsewhere (e.g. Winn 

 and Bardach, 1960; Starck and Davis, 1966). 



The guts of two males (340 and 410 mm) that 

 were speared during midday were full of bits of 

 algae mixed with calcareous powder, organic 

 slurry, and sand (proportions undetermined, but 

 the algae constituted less than 20%), with no 

 evident trace of coral tissue or mucus. 



CONCLUSION. — Scarus ruhroviolaceus is a 

 diurnal herbivore that typically scrapes benthic 

 algae from rock surfaces. 



General Remarks on Parrotfishes 



It is well known that parrotfishes are quiescent 

 at night. They have been thus described in the 

 tropical Atlantic (Winn, 1955; Winn and Bardach, 

 1959, 1960), eastern Pacific (Hobson, 1965; 

 Rosenblatt and Hobson, 1969), Hawaii (Hobson, 

 1972), and elsewhere. EarHer (Hobson, 1965), I 

 suggested that mucous envelopes in resting 

 parrotfishes at night are characteristic of certain 

 small individuals, or of individuals suffering in- 

 jury or stress. The relation between small size and 

 envelope secretion was also noted by Starck and 

 Davis (1966) and by Casimir (1971). Winn and 

 Bardach (1959) believed that the envelope is a 

 defense against nocturnal predators, especially 

 those that sense prey by olfaction or gustation, as 

 do certain moray eels (Bardach, Winn, and Men- 

 zel, 1959). Because the threat from predators in- 

 creases with decreasing size, obviously the smal- 

 ler individuals are in greatest need for protection. 

 Similarly, it is known that injured or distressed 

 fishes are particularly attractive to predators (e.g. 

 Hobson, 1968a), so envelope secretion by 

 parrotfishes suffering these conditions is consis- 

 tent with the idea that the envelopes provide pro- 

 tection. The survey of mucous envelopes in Kona 

 shows a decreasing incidence with increasing size. 

 Nevertheless, Winn and Bardach (1960), working 

 with Scarus vetula at Bermuda, found that certain 

 individuals in aquaria produced the envelope ir- 

 regularly, and Smith and Tyler (1972) found that 

 one individual of that species observed on a reef in 

 the Virgin Islands formed an envelope on some 

 nights, but not on others. Probably this variation 

 within individuals occurs in other species too, but 

 the question was not examined in Kona, where 

 only certain males of iS. ruhroviolaceus were rec- 



ognized as individuals, and these were never seen 

 in envelopes. 



There is controversy over the diet of 

 parrotfishes. Hiatt and Strasburg (1960) reported 

 a diet of living coral not only in S. sordidus, as 

 noted above, but also in all other scarids they 

 examined in the Marshall Islands. I found no evi- 

 dence that any of the species in Kona, including S. 

 sordidus, feed on living coral. Randall ( 1967) simi- 

 larly concluded that parrotfishes in the West In- 

 dies do not feed on living coral; he noted the large 

 amount of sand in the guts of parrotfishes, and 

 suggested that this material, taken purposefully, 

 aids in grinding plant tissue — the primary food 

 — in the pharyngeal mill. 



Although I classify all parrotfish species in 

 Kona as herbivores, their large gut loads of cal- 

 careous powder, organic slurry, and sand seem, too 

 great a proportion of the total contents to have 

 been taken only incidentally, or to be adaptive 

 only because it aids in grinding up plant tissue. 

 There is need to look closer at how parrotfishes 

 utilize the material they ingest. 



Family Blenniidae: combtooth blennies 



The combtooth blennies are most numerous in 

 tide pools and close to rocky shores, where fre- 

 quently they are the dominant fishes. However, 

 this report considers only those species that occur 

 regularly in water deeper than 5 m. 



Exallias brevis (Kner) — pao'o kattila 



Because^', brevis is distinctively hued and habit- 

 ually perches in exposed positions during the day 

 (Figure 37), it is frequently noticed even though it 

 is not especially numerous. It rarely leaves the sea 

 floor and usually rests immobile except when 

 scraping the surface of living coral with its comb- 

 like teeth. After dark, it is secreted in reef crev- 

 ices and seen only occasionally. 



Of the 10 specimens (94: 70-106 mm) ex- 

 amined, 2 that were taken from under partial 

 cover at night (between 4 and 5 h after sunset) 

 contained only well-digested fragments, whereas 

 only 1 taken during the day was empty, and the 

 other 7 were full of food, including fresh material. 

 The major item in all seven (over 90% of the con- 

 tents in each) was scleractinian corals — both 

 skeletal and tissue fragments, along with much 

 mucus. The remaining identifiable items in the 

 diet were fine filamentous algae and diatoms. 



998 



