Meeting Abstract
The marine herbivorous fish Cebidichthys violaceus is considered an obligate herbivore in nature. C. violaceus has an expandable distal intestine in which microbial fermentation occurs and where there are microbially-derived digestive enzyme activities. We observed that as C. violaceus consumed more protein and less fiber, they ate less, and their distal intestine was smaller, yet the fish grew well and showed no mortality across an 8-month feeding trial on omnivorous and carnivorous diets in the laboratory. We hypothesized that the C. violaceus distal intestine microbial community changed in composition in response to increasing protein and decreasing fiber in its diet. Thus, we analyzed microbial diversity using 16s rRNA sequences, microbial fermentation via concentrations of short chain fatty acids (SCFA), and gut and metabolic function via transcriptomic profiles of distal intestine and liver tissue, respectively. The microbiome of distal intestine gut tissues in wild individuals and those fed an herbivorous diet were dominated by Actinobacteria and Proteobacteria, whereas digesta contents of this gut region were dominated by Bacteroidetes and Firmicutes (with B:F ratios of 5:1; more detailed analyses underway). These general phylum-level patterns varied little on an omnivorous diet, but the carnivorous diet caused a complete shift of the microbial community towards unknown bacterial taxa, and Spirochaetes. The SCFA (via gas chromatography) and transcriptomic (featuring greater than 15 million reads per sample) analyses are in progress. Overall, this study will answer whether an herbivorous fish can deal with a carnivorous diet (from digestive and metabolic standpoints) and what this means in terms of dietary specialization.
