HOBSON: FEEDING RELATIONSHIPS OF FISHES 



Order Pleuronectiformes 

 Family Bothidae: left-hand flounders 



Bothiis manciis (Broussonet) — pakVi 



This flatfish is most numerous lying immobile 

 where rocks are interspersed with small patches of 

 sand. It changes its coloration to match closely 

 that of whatever substratum it happens to lie on, 

 rocks or sand. When on sand, it is frequently 

 buried except for its eyes. No change was noted in 

 the overt behavior of this fish between day and 

 night. 



Eight specimens (223: 137-277 mm) were 

 speared at various times of the day. Both indi- 

 viduals collected within an hour after sunrise 

 were empty, whereas of six taken during after- 

 noons, two were empty and four contained well- 

 digested fish remains that appeared to have been 

 in the stomachs at least several hours when col- 

 lected. 



Hiatt and Strasburg (1960) reported this 

 flounder on both rocks and sand in the Marshall 

 Islands and noted a diet comprised primarily of 

 flshes that live in sandy areas adjacent to coral. 

 Most prey species listed by them are fishes (balis- 

 tids, labrids, pomacentrids, and blennies) that 

 probably are active in exposed positions only dur- 

 ing daylight. They believed that B. mancus 

 responds only to moving prey; if so, at least most of 

 its prey, which rests at night, would not be avail- 

 able after dark. The prey listed by Hiatt and Stras- 

 burg also included two species of apogonids, mem- 

 bers of what seems to be a universally nocturnal 

 group; however, during daylight these particular 

 apogonid species congregate in exposed positions 

 close among the coral, where they would seem 

 available to diurnal predators. 



CONCLUSION. — Bothus mancus preys on 

 small fishes during the day. Its nocturnal habits 

 remain uncertain. 



General Remarks on Left-hand Flounders 



Bothids are the most numerous flatfishes on 

 tropical reefs. In the West Indies, Randall (1967) 

 found fishes the major prey of Bothus lunulatus 

 and B. ocellatus, both of which occur on sand 

 patches around coral reefs, often largely buried. In 

 the Florida Keys, Starck and Davis (1966) found 

 B. ocellatus in sandy areas of all reef zones, and 

 although they did not examine its food habits, 

 they inferred from its behavior that it preys after 

 dark on the various small nocturnal invertebrates 

 active on the sand at night. 



Order Tetraodontiformes 



Family Balistidae: triggerfishes 



Melichthys niger (Bloch) — humuhumu 'eleele 



During the day, M. niger typically hovers in 

 loosely spaced aggregations several meters above 

 the reef. Each individual independently picks 

 material drifting in the mid-waters. It is a 

 wary animal that dives to holes in the reef when 

 alarmed. It enters these same holes at nightfall 

 and rests there on its side until morning. 



All seven individuals (165: 122-195 mm) 

 speared from among those active above the reef 

 during the day were full of food, as listed in Table 

 63. The major food items are fragments of fleshy 

 algae — filamentous and foliaceous — probably 

 most of which are drifting in the mid-waters when 

 taken. This triggerfish feeds at least occasionally 

 on the sea floor, as indicated by the relatively high 



1005 



