Chen, Li-Shu (2002) Post-settlement diet shift of Chlorurus sordidus and Scarus schlegeli (Pisces: Scaridae). Zoological Studies, 41 (1). pp. 47-58.

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Abstract

Ontogenetic changes in the development of feeding structures and feeding habits of juvenile parrotfishes Chlorurus sordidus and Scarus schlegeli (Family: Scaridae) were examined at Lizard Island on the northern Great Barrier Reef, Australia. A shift from omnivorous feeding to feeding on plant materials was observed, and this occurred over the size range of 15-30 mm TL. Ontogenetic changes were observed in teeth as well as in gut coiling patterns. Individual teeth were present in newly settled scarids (10 mm TL) but were totally lost when size increased to 26 mm TL. The change in gut coiling patterns occurred mainly in the mid-intestine, from being non-constricted to having a constricted ilial wall. The tracts also changed from 1 sinistral loop to 2 loops by the end of the observation period. The difference in gut length between the 2 species was caused by the different coiling patterns. Small individuals (15 mm TL) of both species were omnivorous with diets dominated by crustaceans and foraminifera. Significant increases in the amounts of algal material and sediment taken were seen as fish grew. With respect to microhabitat utilization, both species fed mainly on dead coral and rocky substratum. Algae, with their associated high density of crustaceans, were used by both species as a feeding substratum when individuals were small (TL < 20 mm). Dietary changes of post-settled C. sordidus and S. schlegeli were directly related to morphological changes in the alimentary tract rather than the differences of habitat utilization.

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