Documentation of the seasonal feeding habits and ability to
assimilate algae are presented for the first time for a North American
grazing stream fish. The chiselmouth, Acrocheilus alutaceus, begins
feeding on algal matter in early spring and has deposited large fat
reserves prior to an early summer spawning season. A sharp decline in
body fat content is then associated with a reduction in food intake at the
onset of spawning. A subsequent increase in food intake, possibly with
a higher energy value due to the inclusion of animal material, quickly
restores fat reserves which then remain high through a period of almost
exclusive herbivory (particularly on diatoms) in the late summer and fall.
With the onset of winter, the diet of A. alutaceus shifts toward omnivory.
Diatoms of the genera Cymbella, Gomphoneis, Synedra, and Melosira form the
bulk of the diet. Both diatom and green algal food sources were
assimilated by A. alutaceus, but at relatively low efficiency. The
efficiency of assimilation of Ulothrix varied inversely with ration size,
while the assimilation of diatoms was unaffected by ration size. Fiber
was not assimilated. The protein fraction was assimilated more
efficiently (44%) than total energy (33%).
The order of preference evidenced in A. alutaceus feeding trials
was: diatom > bluegreen > green > "mix" > moss. The ratio of digestible
protein to digestible energy (P/E) in the food sources proved an excellent
descriptor of observed preference. However, a linear combination of fiber
content (as a negative factor) and gross P/E (as a positive factor)
provided an analytically simpler descriptor and also predicted the correct
order of preference.
Chiselmouths apparently live much longer (22+ yrs) than was
previously known (6 yrs). Formation of the opaque zone, generally
recognized as indicating a growth period, is most evident on A. alutaceus
otoliths from July through October. This coincides with the period of
highest food intake and peak contribution of diatoms to the natural diet. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/38064 |
| Date | 10 August 1990 |
| Creators | Lassuy, Dennis R. |
| Contributors | Li, Hiram W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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