USF St. Petersburg campus Master's Theses (Graduate)

First Advisor

Major Professor: Deby Cassill, Ph.D

Second Advisor

Melissa Green, Ph.D

Third Advisor

Sean Doody, Ph.D


University of South Florida St. Petersburg

Document Type


Publication Date


Date Issued

July 8, 2019


The eastern mosquitofish, Gambusia holbrooki, is a surface-dwelling guppy native to the southeastern United States. While resilient to poor water quality, the fish is a voracious predator of the epilimnion, with established populations in most subtropical/tropical regions with surficial freshwater. Eastern mosquitofish are farmed and collected for use as biocontrol agents against the spread of many infectious, often life-threatening, mosquito-borne illnesses. I compared the reproductive success (fertility) of 370 gravid mosquitofish among 32 sites across central Florida to test the hypothesis that fertility is influenced by maternal, ecological, and environmental factors. I found that fish fertility (clutch size) differed significantly by region (Fig. 13a; R2 = 0.02, p < 0.0001), habitat classification (Fig. 13b; R2 = 0.007, p < 0.0001), preserved female weight (Fig. 13c; R2 = 0.58, p < 0.0001), total dissolved solids (Fig. 13d; R2 = 0.006, p = 0.0004), and conductivity (Fig. 13e; R2 = 0.007, p = 0.003). The strongest predictor of G. holbrooki clutch sizes was female weight, which accounted for 87.8% of the observed variation in fertility. Regional distribution was the strongest predictor of eastern mosquitofish weight. Water quality was a relatively weak predictor of mosquitofish characteristics and fertility. I found that females make significant (189%) post-fertilization nutrient contributions to developing embryos. To my knowledge, my study is the first to quantify maternal contributions to developing embryos in G. holbrooki. Gravid females displaying superfetation developed two clutches at different developmental stages simultaneously and were nearly three times as fertile as those not.


A thesis submitted in partial fulfillment of the requirements for the degree of Masters of Science in Conservation Biology Department of Biological Sciences College of Arts and Sciences University of South Florida St. Petersburg

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