Ontogenetic diet shifts and prey selection among age-0 and age-1 paddlefish

Author

Nicolle MacVey, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2013

Degree Name

Master of Science

Department

Zoology

First Advisor

Garvey, James

Abstract

Many fishes are planktivorous during early life and switch to piscivory or consume larger food items as ontogeny progresses. In contrast, paddlefish begin life as active feeders selecting for larger organisms and then switch to planktivory as they grow. Few studies have quantified these changes in early life foraging. I identified distinct early life foraging behaviors and prey preferences of age-0 paddlefish and how these change with habitat and paddlefish size. Gut contents of 189 age-0 wild paddlefish were used to determine which prey are most preferred and whether habitat variables and paddlefish size influence diet composition. I also performed an experiment to identify differences in foraging behavior and prey preference between age-0 and age-1 paddlefish. Dominant prey, based on percent by number and percent occurrence, of wild age-0 paddlefish ranging from 10 to 116 mm TL was trichoptera larvae (28.5%N, 67.7%O) and hemiptera (18.3%N, 51.3%O). Prey size increased with size of age-0 paddlefish. However, the highest ratio of zooplankton to invertebrates in the gut occurred in a 60 mm paddlefish. The size range of fish in this study was likely too narrow to confirm presence of an ontogenetic diet shift. Habitat had no effect on diet. My experimental study revealed that if provided a mixture of organisms, age-0 paddlefish will primarily consume macroinvertebrates while age-1 paddlefish will mainly filter zooplankton, but occasionally consume larger organisms. Features of river channels (e.g., woody snags, gravel beds in the photic zone) that contribute to the diverse diet paddlefish require in early life may ultimately increase survival and recruitment.