| Summary |
While residing in shallow seagrass habitats each summer, pinfish, Lagodon rhomboides, have been observed to consume a diet dominated primarily by seagrasses and algal material. It had been previously demonstrated that pinfish have anaerobic bacteria associated with their gastrointestinal tract that produce carboxymethylcellulase. However, it is not known whether pinfish derive any nutritional benefit from the presence of these microbes or if the microbes produce metabolic by-products [volatile fatty acids (VFAs)], which could provide energy from the plant material in a manner similar to that found in ruminants. The purposes of this study were to: 1) determine if there was an ontogenetic change in diet for pinfish in the population studied; 2) characterize the types and quantities of VFAs found in the intestinal tract of pinfish that may be produced by the intestinal microbiota; 3) determine if there are ontogenetic changes, similar to that observed previously for diet, in the type and amount of VFA present in the intestinal tracts of pinfish; 4) determine if radioisotopic cellulose injected into the intestinal lumen could be converted into microbial proteins, free glucose, or VFAs from anaerobic fermentation of cellulose by microbiota in the intestinal tract; and 5) determine if the VFAs or other molecules produced by microbial metabolism are assimilated by pinfish. Chapter 1 describes gut content analysis and VFA analysis. Pinfish [20 - 175 mm standard length (SL)] were collected from a seagrass meadow, their stomach contents were analyzed, and the quantity of VFAs was measured using high-pressure liquid chromatography (HPLC). Pinfish consumed both plant and animal material, but the amount of plant material increased significantly with fish standard length from 10.1 % in 20-39 mm SL fish to 45.4 % in 120-152 mm SL fish. Eight volatile fatty acids (formate, acetate, lactate, propronate, butyrate, isobutyrate, valerate, and isovalerate) were identified in the intestinal tract of pinfish. Acetate was the most frequently occurring VFA, being found in 71 % of all fish tested. There was an increase in the median number of VFA species from two to three during ontogeny, but the increase was not significant. Chapter 2 describes the radioisotopic cellulose injection study. The intestinal tracts of anesthetized live pinfish were injected with radioisotopic '''C-cellulose. The amounts of radioisotopically labeled cellulose converted to VFAs, glucose, and microbial protein in the intestinal tracts were determined using HPLC, thin-layer chromatography (TLC), and trichloroacetic acid (TCA) precipitation respectively. The amount of radioisotope in the intestinal contents was greatest in microbial protein, followed by VFAs and lowest in glucose. Radioisotopic VFA amounts in the intestinal contents decreased over the 12-hour incubation period, suggesting that the radioisotopic VFAs were then assimilated by the pinfish. Overall pinfish had assimilated an average of 7.0% (SE± .069%) of the radioisotopic cellulose into muscle and liver tissues and 10.0% (SE ± 0.0%) after one hour of incubation. The amount of radioisotope assimilated in pinfish tissues dropped over the twelve-hour incubation interval. There was an ontogenetic change in diet with a significant increase in the proportion of plant material. |
