Author : Gretchen Lynn Skea
Publisher :
ISBN 13 :
Total Pages : 266 pages
Book Rating : 4.:/5 (119 download)
Book Synopsis Carbohydrate Digestion in Marine Herbivorous Fishes by : Gretchen Lynn Skea
Download or read book Carbohydrate Digestion in Marine Herbivorous Fishes written by Gretchen Lynn Skea and published by . This book was released on 2006 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this thesis was to examine the enzymatic degradation of algal carbohydrates by marine herbivorous fishes to determine which dietary carbohydrates are digested directly by the fishes, which are available for microbial fermentation, and which remain undigested. Enzyme extracts were taken serially along the gut from the gut wall, gut fluid and microbial pellet of Girella tricuspidata, Girella cyanea, Kyphosus sydneyanus, Aplodactylus arctidens, Aplodactylus etheridgii, Parma alboscapularis and Odax pullus and tested for activity against starch, laminarin, carrageenan, agarose, alginate, fucoidan and carboxymethylcellulose. In all species, hydrolysis of starch was greater than for all other substrates tested and was highest in the gut wall and anterior gut sections, indicative of endogenous origin. Activity in the anterior gut wall varied between species in the order G. tricuspidata (23607 units min−1) > G. cyanea (15664 units min−1) > A. etheridgii (6464 units min−1) ) > P. alboscapularis (5303 units min−1) > A. arctidens (3327 units min−1) > K. sydneyanus 1295 units min−1) > O. pullus (501 units min−1 ). In all cases hydrolysis of starch declined rapidly in the gut fluid with progression along the gut. Amylolytic enzymes in K. sydneyanus and A arctidens are the result of a-amylases, which display peptide sequence homology to a-amylases from other vertebrates including marine fishes. Activation energies indicate that a-amylases from K. sydneyanus and A. arctidens are more efficient at low temperatures, consistent with the distribution of these species. Enzyme activity against all other carbohydrates was lower than that against starch and varied considerably between species. Microbial extract of A. etheridgii displayed the highest activity against carrageenan and agarose in all gut sections, reaching maxima of 47 units ml−1 against carrageenan and 35 units ml−1 against agarose in the mid-gut microbial extract. This is much higher than for the other non-starch carbohydrates tested, indicating that these enzymes are potentially important substrates for microbial fermentation in A etheridgii. Carrageenases from A. etheridgii and A arctidens were examined more closely and found to have some peptide sequence homology to sulfatases from marine bacteria as well as novel sequence. Carrageenases studied have properties consistent with their environment including low temperature optima, indicative of cold-adaptation. Overall results of this research indicates that the study species fall along a continuum from maximizing throughput and digesting easily hydrolysed substrates in the foregut to relying more heavily on microbial fermentation in the hindgut.