Ontogenetic niche shifts are critical times in a fish's life that need to be passed for
survival, growth and recruitment (Gerking 1994, Osenberg et al. 1994). These niche
shifts are identified by a change in feeding from one prey type to another. These shifts in
feeding occur throughout growth and can be related to changes in gut morphology and
mouth position (Stewart 1926, Macphee 1960).
The shortnose sucker (SNS) Chasmistes brevirostris was listed as endangered in
1988 with little known about it's feeding habits. Previous diet studies include a
qualitative study of adult gut contents (Hazel 1969) and a quantitative study of juvenile
gut contents (Buettner and Scoppettone 1990). Both studies examined gut contents of
SNS caught during daylight hours.
This study quantifies gut contents of juvenile SNS and relates diet to ontogenetic
changes in gut length, mouth and time of day. In addition, a selectivity index was used
to compare gut contents and potential prey to determine if juvenile SNS exhibit
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