Ciliated protozoans as food for first-feeding larval grouper, Epinephelus septemfasciatus: Laboratory experiment

The survival from hatching to day 8 of larval grouper, Epinephelus septemfasciatus, was examined in two rearing experiments. In Experiment 1, the larvae were fed with aloricate ciliates, Euplotes sp. 1 or Euplotes sp. 2, at different concentrations. Significantly higher survival of the larvae was observed in the treatment with the highest density of Euplotes sp. 1 (1.4 x 10⁴ cells l^-1) on days 5 and 6 after hatching. Experiment 2 consisted of different prey concentrations of a loricate ciliate, Favella taraikaensis. Significantly higher larval survival was observed in the treatment having the highest density of F. taraikaensis (4.8 x 10³ cells l^-1) on days 4-6 after hatching. Larval gut content analyses failed to show any ciliates in Experiment 1, whereas hard body parts of F. taraikaensis were detected in Experiment 2. However, feeding on Euplotes by grouper larvae was confirmed by labelling the former with fluorescent microspheres. The lack of ciliate remains in Experiment 1 might be due to complete digestion by the larvae. The present experiments demonstrated that the higher ciliate densities enhanced larval survival until 4-6 days after hatching, suggesting the importance of ciliates as initial food for first-feeding E. septemfasciatus. It is likely that ciliates in the marine ecosystem may bridge the gap until grouper larvae can encounter foods such as copepod nauplii.