ISOLATION OF CELLULOLYTIC MICROBES FROM THE INTESTINAL-TRACT OF THE PINFISH, LAGODON-RHOMBOIDES - SIZE-RELATED CHANGES IN DIET AND MICROBIAL ABUNDANCE

Pinfish, Lagodon rhomboides (Linneaus), undergo a gradual ontogenetic dietary shift during their first year of life, marked by an increase i n the consumption of plant material. To determine if this shift in die t was associated with a change in the microbial flora of the intestina l tract that may assist in degradation of plant material, stomach cont ents were analyzed and microbes in the intestinal tract were isolated from fish ranging from 20 to 139 mm standard length. These fish were c ollected from Core Sound, North Carolina, USA between March and Septem ber 1991. Plant material increased from 16 % of dry weight of stomach contents in pinfish under 40 mm standard length (SL) to 65 % in pinfis h above 120 mm SL, confirming previous observations of a diet-related ontogenetic change in L. rhomboides. Comparison of the total cultivata ble facultative and anaerobic microbial flora isolated from the intest inal tract contents of pinfish ranging in size from 26 to 139 mm SL sh owed a 10-fold increase between fish < 40 and fish > 40 mm SL, with ma ximum population densities of approximately 2 x 10(7) colony forming u nits (CFU) g-1 of intestine including contents. The percentage of micr obial isolates examined capable of hydrolyzing carboxymethylcellulose (CMC) increased from 12 % in fish < 40 mm SL to 13 to 50 % in fish > 4 0 mm SL, although there was no strict increase with increasing fish si ze classes. Although the percentage of CMC-hydrolytic microbial isolat es varied with respect to fish SL, the percentage of skim-milk hydroly tic (proteolytic) isolates remained relatively constant (4 % of total isolates) irrespective of fish SL and dietary composition. Results pre sented in this study document the first isolation of carboxymethylcell ulose producing microbes from the intestinal tract of any fish and dem onstrate that the ontogenetic dietary shift in L. rhomboides is parall eled by qualitative and quantitative changes in the intestinal microbi al community. The use of strict anaerobic sampling methods in the prep aration of intestinal contents from wild-captured fresh specimens was essential in obtaining these isolates.