Masters Theses

Date of Award

8-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Zoology

Major Professor

Melbourne C. Whiteside

Committee Members

Sandy Echternacht, David Etnier

Abstract

The distribution and diets of larval Pomoxis niqromaculatus (Lesueur) and Lepomis spp. were estimated from collections during the summer of 1984 from Lake Itasca, Minnesota. Zooplankton was sampled concurrently with fish and used to estimate changes in zooplankton density and to calculate electivity indices in comparison with the fish stomach contents. Block croppies (Pomoxis niqromaculatus) hatched during the first two weeks of June, moved into the limnetic zone for approximately one month, and returned to the littoral zone. Sunfish (Lepomis spp.) hatched from mid-June to mid-July; some of the larvae undertook a pelagic migration, but many apparently remained inshore. Larval croppies ate copepod nauplii at the initiation of feeding, but soon switched to and fed primarily upon cyclopoid copepods. Larval sunfish ate predominantly rotifers and copepod nauplii.

During the first week of July, a decline was observed in numbers of pelagic zooplankton which concurred with intensive feeding by young croppies and sunfish. Croppies were probably not abundant enough to be a major factor in this decline. An increase in the mean size of zooplankton over the summer was probably due to the decrease in the numbers of rotifers, which could hove resulted from larval fish predation. Predation by larval fish may play a part in structuring zooplankton communities by eliminating small size classes, and may also be a major factor in the mid-summer decline of zooplankton. Larval centrarchids interact with a combination of fishes to produce these effects.

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