Studies on the feeding habit and digestive mechanism of parrotfish (Scarus ghobban)
| Autor: | Meng Ju, Chou, 周孟儒 |
|---|---|
| Rok vydání: | 2002 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 90 Parrotfish (Scaridae) is a dominant fish species living in coral reefs. It is considered a high priced food fish transported and sold live. Due to the market demand and overfishing, parrotfish have been endangered in nature. Thus created stress to the coral reef by overgrowth of algae on coral, otherwise are cleaned up and consumed by parrotfish. Although, the health of coral reef has gone through annual checkup in Taiwan, and the ecology of parrotfish has also been investigated in recent years, the feeding habit and the digestive mechanism of parrotfish has not been much studied. It is the objective of this study to understand how the food intake is digested, and whether the parrotfish is herbivore. Three proteases were found in the crude extract of digestive tract in Scaridae at initial phase. The optimal pH was found at 3.0, 7.0, and 9.0, the optimal temperature was 55 °C. Trypsin-like, chymotrypsin-like and carboxypeptidase B were identified in gut using synthetic substrates. Maximal amylase activity was found at pH 7.0 and 9.0, and the optimal temperature was 50 ~ 55 °C using soluble starch as substrate. Both exo-1,4-b-glucanase and laminarinase showed maximal activity at 50 °C, and two activity peaks at pH 5.0 and 8.0. Laminarinase had an additional activity peak at pH 3.0. The digestive enzyme activity was lower in pharyngeal mill pouch and oesophagus (I) than in intestine of Scaridae. Protease and laminarinase were active between intestine bulb (II), and posterior intestine (V) where protein and structural b-1,3-polysaccaridaes of algae are digested. High levels of exo-1,4-b-glucanase activity occurred on the anterior intestine (III) and mid-intestine (IV), where gross breakage of structural b-1,4-polysaccaridaes of the cell walls took place. The thylakoid membrane of Rhodophyta were digested and the hydrophilic phycobiliprotein released. Proteolytic activities hydrolyzed the protein moiety and resulted in free phycoerythrobilin which was absorbed in the posterior intestine (V), where the tissues appeared red. Amylase activity was the highest in the posterior intestine (V). Histochemical observation showed that the villi of this gut segment V appeared in larger size and more finger-like papillae than mid-intestine (IV) and provided larger absorption surface. Posterior intestine (V) seemed to be the main digestion and absorption site for algal storage polysaccharides. Parrotfish had a ratio of amylase to protease activity of 27.55 and relative gut length 1.40. The two indices were in the range between omnivorous and carnivorous suggesting that Scaridae is omnivorous. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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