Characterizing the resident, fermentative microbial consortium in the hindgut of the temperate-zone herbivorous fish, Hermosilla azurea (Teleostei: Kyphosidae)
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The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California (33°19′42′′N; 118°18′37′′W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment, and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse, fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified, Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides,Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the breakdown of algal polysaccharides in the herbivorous diet of the fish.
KeywordsDigestive Tract Desulfovibrio Herbivorous Fish Algal Polysaccharide SCFA Level
We thank Captain J. Cvitanovich and the crew of the R.V. Yellowfin for their help in capturing fish. We also thank W. Van Antwerp for performing SCFA analyses, E. Sturm for leading several expeditions to collect fish, and E. DeLong for his generous donation of PCR primers. T. Parker, J. Ferreira, W. Katzenstein, C. Hamilton, D. Tessier, S. Ecker, J. Haygood, and D. Asher provided valuable assistance with fish collection and lab work. The Departmental Associations Council and the Department of Biological Science at California State University, Fullerton, provided financial support. All experiments herein comply with the laws of the United States of America.
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