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Effects of fish on zooplankton

Brian Allman, Muska Fahim, Megan May, Cody Roldan, and Ryan Edelen
Aquatic Ecology class, BIO 390, Biology Department, DePauw University
Spring semester 2010

We conducted an experiment to assess the effect of fish on zooplankton abundance and composition in the lab. 

We hypothesized that addition of fish would reduce the abundance of large zooplankton (cladocerans, copepods) and increase the abundance of small zooplankton (rotifers).

We set up four tanks in the lab, three with fish and three without fish.  We purchased fish from a pet store and collected water from the Quarry Pond in the DePauw Nature Park.  We introduced four types of zooplankton into each tank:  cladocerans, copepods, rotifers, and nauplius larvae.  We added dissolved nitrogen and phosphorus to each tank one week before the experiment began.  We measured chlorophyll, dissolved oxygen, conductivity, temperature, pH, nutrient levels, and abundance of bacteria and zooplankton. 

Addition of fish changed the aquatic environment.  There were increases in abundance of smaller zooplankton, bacteria, and chlorophyll.  Abundance of larger zooplankton (cladocerans, copepods) was reduced.  Dissolved oxygen content and pH decreased.  

Future projects should investigate food availability for zooplankton and should use a larger sample size, more clearly defined procedures, and a more natural environment (soils, fish, other abiotic and biotic factors).