Catfish aquaculture remains the largest sector of the U.S. aquaculture industry, grossing ~$447 million in sales in 2022. Producers are plagued by annual losses associated with the trematode Bolbophorus damnificus. Management focuses on controlling the snail intermediate hosts using copper sulfate. Herein, the effects of copper on larval stages of the trematode Drepanocephalus spathans and Austrodiplostomum compactum eggs were investigated. Results indicate copper treatments currently used to control snails are ineffective at precluding hatching of trematode eggs. Higher doses prevented trematode eggs from hatching, although these levels are likely impractical in a commercial setting. A second study investigated the effects of temperature on miracidia of D. spathans development and hatching. Eggs were collected from digesta of double-crested cormorants and stored at 4 °C until analysis. Data generated from these studies indicate D. spathans eggs hatch from 12–22 days after removal from cold storage to 26–30 °C, but hatching was not observed at temperatures <20 °C.

This thesis consists of four research papers. In the first paper we study whether certain properties of sets (functions) are separably determined. In our results we use the "method of elementary submodels". In the second paper we generalize some results concerning Valdivia compacta (equivalently spaces with a commutative retractional skeleton) to the context of spaces with a retractional skeleton (not necessarily commutative). The third paper further studies the structure of spaces with a projectional (resp. retractional) skeleton. Under certain conditions we prove the existence of a "simultaneous projectional skeleton" and we use this result to prove other statements concerning the structure of spaces with a projectional (resp. retractional) skeleton. In the last paper we study the method of elementary submodels in a greater detail and we compare it with the "method of rich families". 1