Ecology of Four Apogonids — Strasburg 
341 
Apogon gracilis (Bleeker) and Gymnapogon 
gracilicauda Lachner 
Unlike most Apogonidae, which dwell in 
close proximity to a sheltering substratum, A. 
gracilis and G. gracilicauda are apparently 
pelagic species. They were observed many times 
in the lagoon at Parry Island, Eniwetok Atoll, 
swimming in large, loose schools. Most schools 
were in the general vicinity of coral mounds at 
depths of 12-25 ft, but a few occurred over 
relatively featureless sand or coral rubble at 
the same depth. The gracilis schools were com- 
posed of several hundred individuals, whereas 
the gracilicauda schools were much smaller, 
consisting of perhaps 5—25 fish. The number of 
schools and the number of fish per school in- 
creased with the distance from shore. 
Both fish were difficult to recognize as 
apogonids in life. Their pelagic occurrence was 
unexpected and their colorless glassy transpar- 
ency made them hard to detect and characterize. 
The two could be told apart by the presence 
in A. gracilis of an internal black spot on the 
lower caudal peduncle and the black tip of its 
upper caudal lobe. 
Morphologically, Gymnapogon is quite dis- 
tinct from the rest of the Apogonidae and it is 
not surprising to find it occupying a different 
habitat. A summary of its physical peculiarities 
and their systematic significance has been pre- 
sented by Lachner (1953:490). Apogon gra- 
cilis , on the other hand, is a typical apogonid 
and shows no particular adaptations to a pelagic 
mode of life (except possibly for its colorless 
transparency). The diet of four rotenoned A. 
gracilis consisted of pelagic crustaceans, mostly 
amphipods. 
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