HOBSON: FEEDING RELATIONSHIPS OF FISHES 



Marshall Islands. Randall (1955) reported only 

 brachyuran crabs in the diet of two specimens that 

 he examined from the Gilbert Islands. 



CONCLUSION.— Cirrhituspinnulatus is a noc- 

 turnal predator that hunts mostly xanthid crabs. 



Family Labridae: wrasses 



Bodianus bihiniilatus (Lacepede) — aawa 



This relatively large, solitary wrasse occurs 

 only infrequently on the shallow reefs in Kona as 

 it lives mostly at depths below 15 m. Two indi- 

 viduals (172 and 283 mm) were speared during 

 midafternoon as they moved actively among coral 

 at 25 m along the outer drop-off, and the guts of 

 both were full of crushed mollusks. 



CONCLUSION.— Bo<:/jrtni<.s bilunulatus feeds 

 on mollusks during the day. 



Cheilinus rhodochrous Giinther — po'ou 



This labrid is numerous over both coral and 

 rocky substrata deeper than about 10 m. It is a 

 solitary species that hovers close to the reef during 

 the day and takes shelter in the reef at night. 

 Several times larger individuals attempted to 

 take fish that were impaled on my spear, and twice 

 they succeeded despite my attempts to drive them 

 away. 



Among 16 specimens (175: 129-242 mm) col- 

 lected during afternoons, 6 contained only a few 

 well-digested fragments posteriorly in the gut, 

 and most of the material in the other 10 was far 

 digested. Fish were the major prey, occurring in 4 

 of the 10 individuals that contained identifiable 

 material (mean percent of diet volume: 40; rank- 

 ing index: 16). Other food items were: decapod 

 shrimps in three (mean percent of diet volume: 30; 

 ranking index: 9), brachyuran crabs in one (mean 

 percent of diet volume: 8; ranking index: 0.8), un- 

 identified crustacean fragments in two (mean per- 

 cent of diet volume: 12; ranking index: 2.4), and 

 other unidentified fragments in two (mean per- 

 cent of diet volume: 10; ranking index: 2). The only 

 fish that could be identified was a pomacentrid, 

 - Pomacentrus jenkinsi, and the only identifiable 

 shrimp was Saron marmoratus. Generally C. 

 rhodochrous preys on large organisms, but be- 

 cause it crushes them upon ingestion, 

 identifications are difficult. Presumably crushing 



the food items accelerates digestion, thus con- 

 tributing to the poor condition of this material. 

 However, because all these specimens were col- 

 lected during afternoons, the advanced digestion 

 could also reflect early morning feeding. 



Cheilinus rhodochrous is a stalking predator, 

 equipped by a relatively large mouth and pair of 

 large canine teeth at the front of each jaw to hunt 

 prey that are relatively larger and more active 

 than those taken by most other labrids. Most of the 

 specimens that were examined contained a single 

 large prey organism, indicating that feeding is 

 infrequent and that each successful attack pro- 

 vides enough nourishment to sustain the predator 

 for some time. 



CONCLUSION. — Cheilinus rhodochrous is a 

 diurnal predator that stalks relatively large fishes 

 and crustaceans. It may have peaks in feeding 

 early and late in the day, but is inactive at night. 



Pseudocheilinus octotaenia Jenkins 



This small species is one of the more numerous 

 labrids on coral-rich reefs at depths to at least 30 

 m, but its large numbers are difficult to appreciate 

 because it occurs close among the many narrow 

 interstices of the reef. It is strictly a diurnal 

 species that takes shelter in the reef at night. 



All 12 specimens (77: 50-95 mm) taken during 

 afternoons had material in their stomachs, but the 

 food items were difficult to identify because they 

 were small and had been crushed when ingested. 

 Thus, most of the gut contents of all 10 individuals 

 that contained recognizable material can be listed 

 only as unidentified crustacean fragments (mean 

 percent of diet volume and ranking index: 71.9). 

 Items that could be identified are: brachyuran 

 crabs in three (mean percent of diet volume: 22; 

 ranking index: 6.6), echinoids in one (mean per- 

 cent of diet volume: 5; ranking index: 0.5), demer- 

 sal fish eggs in one (mean percent of diet volume: 

 1; ranking index: 0.1), and copepods in one (mean 

 percent of diet volume: 0.1; ranking index: 0.01). 



CONCLUSION .—Pseudocheilinus octotaenia is 

 a diurnal predator that feeds mostly on 

 brachyuran crabs and other benthic crustaceans. 



Labroides phthirophagus Randall 



This small wrasse (most are less than 100 mm 

 long) is specialized to pick ectoparasites from the 



989 



