<p>This thesis describes the mechanism and the selectivity of food intake in bream ( <u>Abramis brama</u> ). It is a compilation of six articles which have been published (or will soon be published) in international journals.<p>In the first chapter, diets and feeding modes in cyprinid fishes are described, in order to determine the ecological position of bream within the cyprinids. The next step was to develop insight in the actual mechanism of the particle retention. X-ray movies of foraging bream, with marked gill-arches, showed too large inter-arch slits to retain small food-particles. From the 3-D architecture of the branchial sieve, a new model was derived. It assumes that particles are retained in channels on the gill-arches. The actual mesh-size of these channels can be adjusted by insertion of movable gill-rakers from the adjacent gill-arch. Distribution of retained particles in the channels and the path of ingested particles, traced with X-ray cinematography, supported the new model. Selectivity-curves, obtained from feeding-experiments, showed good correlation with curves expected from the model. It appeared that medium sized bream (ca. 20 cm) was able to feed with reduced or with unreduced channels, indicating that these fish are able to adjust its filter. Larger bream (>30 cm) foraged with reduced channels only. Two feeding modes have been observed in bream, particulate feeding (PF): in which individually located prey is attacked individually and filter-feeding (FF): an amount of water is filtered randomly. The switch from PF to FF depends on zooplankton density, swimming speed and buccal volume of the fish. It is assumed that bream switches to FF when zooplankton density andlor buccal volume becomes so large that each random snap will yield at least one prey-item. Consequently, small fish will remain particulate feeder at higher densities than larger fish. Retained particles are to be transported to the oesophagus at low risk for loss. It was found that small prey are enveloped in mucus for transport. Upto 900 zooplankters per bream have been observed in oropharyngeal mucus.
|Qualification||Doctor of Philosophy|
|Award date||4 Dec 1991|
|Place of Publication||S.l.|
|Publication status||Published - 1991|
- feeding behaviour
- Abramis brama