Effects of Invasive Water Hyacinth on Boldness and Habitat Preference in Mosquitofish

Effects of Invasive Water Hyacinth on Boldness and Habitat Preference in Mosquitofish

Alvin Sherman Library

Eastern mosquitofish (Gambusia holbrooki) are small freshwater fish that play an important role in aquatic food webs. Their behavior, especially boldness and risk-taking, can change depending on the type of habitat they occupy. In this study, we investigated how mosquitofish respond behaviorally to the presence of the floating invasive plant water hyacinth by comparing their boldness, preference for cover, and predation rates between water hyacinth and its native competitor, pennywort. Fish boldness was measured using a two-factor latency experiment. Fish were collected from freshwater locations in South Florida that either had the invasive plant or were free of it and placed into experimental tanks that represented three habitat conditions: a control tank with no vegetation, a tank with a native floating vegetation pennywort, and a tank with an invasive floating plant water hyacinth. Fish were released from a holding cage, and the time it took them to emerge into the tank was recorded. Mosquitofish consistently showed faster emergence times in the tank with the native vegetation. This indicates greater boldness in habitats mimicking those conditions. The mosquitofish were slower to emerge in the invasive vegetation tank, suggesting higher hesitation or risk for the fish. The control tank produced intermediate results, meaning the fish behavior fell between the native and invasive conditions. Habitat preference was evaluated through a choice experiment, where fish were able to choose to assemble under the native pennywort plant or invasive water hyacinth. Fish consistently preferred the native plant, but the pattern was stronger for fish collected from sites without water hyacinth. To determine whether these behavioral differences were related to predation pressure, tethered bait trials were also conducted under water hyacinth and pennywort. Predation rates were similar across all habitats, showing that while mosquitofish changed their behavior depending on vegetation type, the overall risk of predation did not differ. These results demonstrate how habitat type influences mosquitofish behavior and provide insight into how freshwater ecosystems may be affected by the spread of invasive aquatic plants.