Effects of marine ciliates on survivability of the first-feeding larval surgeonfish, Paracanthurus hepatus: laboratory rearing experiments

The contribution of ciliates as a food source to survival of first-feeding surgeonfish larvae, Paracanthurus hepatus, was examined in rearing experime nts. The larvae were exposed to eight treatments; i.e. a tintinnid, Amphore llopsis acuta (1.0 x 10(4), 5.1 x 10(3) and 2.2 x 10(3) cells l(-1)) and a naked ciliate, Euplotes sp. (1.3 x 10(4), 8.0 x 10(3) and 5.0 x 10(3) cells l(-1)), plus two controls without ciliates. Highest survival of the larvae over the first 4-8 days was observed in the highest density of A. acuta. R earing experiments also showed that the survivals of larvae fed with A. acu ta were higher than those fed with Euplotes sp. Gut content analyses reveal ed loricae of A. acuta in the larvae. Although Euplotes sp. (lacking lorica e) was never recognized in those larval guts, feeding on Euplotes sp. by la rvae was confirmed using the ciliate labeled with fluorescent microspheres, implying that the feeding on naked ciliates by fish larvae has been overlo oked. The results strongly suggested that both tintinnid and naked ciliates play important roles as alternative food sources to copepod nauplii by enh ancing the survivability of fish larvae, especially those with a smaller mo uth.