Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 84-97).

This study is another phase of the overall research program designed to furnish basic information for the management of East Texas lakes and has as its specific purpose the determination of the age and growth characteristics of two valuable species on these waters. The species to be considered are the black crappie, Pomoxis nigro-maculatus (Le Sueur) and the white crappie, Pomoxis annularis Rafinesque. Both species are highly regarded as food fish and have for many years offered recreational outlets for Texas fishermen.

This study is based upon information taken from stomach analysis of 302 black crappie and 561 white crappie; the following data will be presented: 1. Food of adults and fingerlings; 2. Diet variation in relation to food availability; 3. Seasonal variation of feeding habits; 4. Diet variation in relation to size of crappie. Collections were made from ten lakes located in North, East, Central, and South Texas.

Individuals within fish populations differ in many traits, such as sex, life-history, habitat residence, diet, and morphology. Such trait differences among individuals (i.e. intra-population variation) may be greater than the differences among populations (i.e. inter-population variation). My dissertation examines intra-population variation, with a focus on trophic relationships and morphology; as well as how variation in these attributes may reflect differences in bioaccumulation of contaminants. The second chapter of my dissertation examines the influence of spatial-temporal variation on the trophic structures of round goby (Neogobius melanstomus) and two age classes of yellow perch (Perca flavescens) within Saginaw Bay, Lake Huron. Using stable isotope ratios (δ13C, δ15N, δ2H, δ18O) and stomach contents as trophic indicators, I examined variation of diets. I found that spatial variation had a greater impact on diet indicators than both annual and seasonal variation. This spatial variation could represent a form of compartmentalization within the community of fish residing in Saginaw Bay, and could provide stability to the community. Chapter three of my dissertation examines intra-population variation in yellow perch morphology through a series of mesocosm experiments. My first mesocosm study determined that yellow perch could be experimentally manipulated to display divergent morphologies using simulated habitats, specifically pelagic and littoral habitats. Following this experiment, I focused on specific environmental drivers (structure, prey resources, and predation risk) as possible influences on yellow perch morphology. Within experimental pools, I exposed yellow perch to one of four treatments (an open pool, a structured pool, pools with chironomid prey resources and pools with a perceived, olfactory, predation risk) in the summer of 2015. Following exposure to these treatments I examined the morphological changes in yellow perch in magnitude and direction. I observed that while each treatment induced some difference in morphology, the open and structured treatments had the greatest magnitude of difference. I repeated the open and structure treatments during the following summer (2016). Again, I found that structure and open morphologies could be induced by my mesocosm treatments, but also observed that shapes differed from the previous year’s structure and open treatments. Finally, my fourth chapter examined how variation in trophic niches and morphology may reflect variation in contaminant concentration of fish in their natural environment. In this chapter, I extended my work with yellow perch to also include black crappie (Pomoxis nigromaculatus) and examined fish from 5 northern Indiana glacial lakes. Using model inference techniques, I found that variation in mercury was closely associated with not only fish total length, but also stable isotopes (δ13C and δ15N) and morphology. Interestingly, morphology-related variables of both species were strong predictors of mercury concentration in fish, following total length. Together, the chapters within my dissertation highlight the importance of considering intra-population variation, in which local factors such as habitat conditions and prey availability can influence individual variation in trophic structuring and morphology. These in turn may reflect other attributes of interest, such as the accumulation of contaminants.

This thesis examines the reproductive cycles of five species of Texas centrarchids: the largemouthed black bass, the black crappie, the bluegill, the redear sunfish, and the striped bass. In this report attention is given to the reproductive cycles of the five species for a period of one year.

White Crappie (Pomoxis annularis) and Black Crappie (P. nigromaculatus) are popular North American gamefish; however, frequent fluctuations in year class strength present a management challenge for recreational fisheries. Intensive aquaculture production has the potential to address this challenge through controlled hatchery reproduction for supplemental stocking, but further study is needed to refine and optimize techniques. Therefore, this study evaluated the effects of hormone injection timing on latency period and spawning success, examined effective cryopreservation techniques for black-stripe Black Crappie sperm (a preferred hatchery phenotype), and compared simulated spring duration on out-of-season spawning success. Latency period for White Crappie did not depend on the diel time of gonadotrophin-releasing hormone injection. Cryopreservation of black-stripe Black Crappie sperm and subsequent fertilization of White Crappie eggs was more effective using 5% dimethyl-sulfoxide than 10% methanol. A longer duration at final spring spawning conditions (3 vs. 2 weeks) increased egg fertilization in out-of-season spawning experiments.