Endosymbiotic communities of two herbivorous labroid fishes,Odax cyanomelas andO. pullus

Two herbivorous species of the temperate labroid fish family Odacidae were examined for the presence of gut endosymbionts.Odax cyanomelas (Richardson) from southern Australia andO. pullus Schneider from New Zealand both feed on macroalgae, yet appear to lack obvious morphological specializations for herbivory. Specimens ofO. cyanomelas andO. pullus were collected in 1989 from Sydney, Australia, and Leigh, New Zealand, respectively. Both species were found to harbour dense concentrations of prokaryotic and eukaryotic microbes in their lower intestines. The various cell types present were examined by light microscopy, transmission electron microscopy and scanning electron microscopy. Epifluorescence microscope counts were used to quantify the distribution and abundance of the microbiota along the gut ofO. cyanomelas. Major differences were observed in the composition of microbiota between the two species.O. cyanomelas contained spirilla, large rod-shaped bacteria, filamentous bacteria and two forms of trichomonad flagellates.O. pullus also harboured dense, large, rod-shaped bacterial populations, but lacked the other two large prokaryote categories found inO. cyanomelas, and contained diplomonad flagellates. The large rod-shaped bacteria found in both species resembled prokaryotes described from other herbivorous fish and termites.