Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Fall 2025

Thesis Director

Eden L. Effert-Fanta

Thesis Committee Member

Robert E. Colombo

Thesis Committee Member

Joseph J. Parkos III

Abstract

Across the United States, fisheries managers and agencies continue to battle the spread of invasive bigheaded carp (Hypophthalmichthys spp.). Although previous research has identified environmental parameters such as temperature and flow to be triggers of spawning activity, many of these studies focus on larger rivers, rarely focusing on the specific thresholds or timing of when a spawning event takes place. I utilized the differing hydrology of the Illinois and Wabash Rivers and their tributaries to examine the differences in environmental parameters needed to trigger bigheaded carp reproduction. Three mainstem sites and three tributaries of both basins were sampled for ichthyoplankton (eggs and larvae) from April-August 2023-2024. Environmental data, discharge and water temperature, were collected and compared along with ichthyoplankton catch and density between years, sites, and months. A select number of eggs were also staged (aged) and had their fertilization times estimated. I found a large difference in reproduction between 2023 and 2024. Differences in water temperature and river discharge were also found between the two years. Ichthyoplankton levels in tributary sites of both basins were found to have a more sensitive response to discharge than mainstem sites. Additionally, I found discharge to have a greater influence on reproduction than temperature, with specific minimum discharge thresholds for spawning activity present in the Illinois River basin. The Wabash River lacked these results due to low levels of reproduction even at low discharges. Illinois River bigheaded carp may also prefer to spawn in evening hours based on estimated fertilization times of eggs. No diurnal patterns of egg fertilization were found in the Wabash River basin. Continued research is needed to understand how reproductive and early life history strategies change across their invaded range. Studying bigheaded carp throughout an array of hydrologic regimes can aid in adapting management strategies to mitigate damages caused by these invasive species.

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