INHS Reports July-August 1997

Differences in Food Consumption and Metabolic Rates Between Walleye Stocks

Distinct fish stocks comprised of one or more populations of the same species can evolve in a variety of ecological conditions. Differences between the stocks are adaptive and can result in different genetic, physiological, anatomical, and life history traits. Thermal regime is one important environmental factor that could influence stock adaptations. Fish from diverse geographical regions may have physiological adaptations to temperature, such as food consumption and metabolic responses that affect growth.

Information about these adaptations between stocks can be used for management decisions. Bioenergetics models are a valuable tool that incorporates food consumption and metabolic parameters as well as information about temperature and fish size to predict growth for a fish population. Resulting growth rates of young-of-the-year fish can be important in determining survival. These models have historically been species-specific rather than stock-specific. We are using a bioenergetics framework for investigating adaptation among fish populations.

Walleye (Stizostedion vitreum) are a popular and economically important sportfish that are often maintained by supplemental stockings. These fish are introduced as fry (approximately 9-15 mm) and a range of fingerling sizes (35-100 mm). These walleye are hatchery produced, and parental strains can be from different source populations throughout the country. We investigated physiological differences between stocks by examining growth, food consumption, and metabolic rates of five different genetic stocks of juvenile walleye (100-150 mm) from four different areas throughout North America: Arkansas (two different strains), Missouri, Wisconsin, and northern Canada.


Recirculation system and environmental chamber at INHS Kaskaskia Biological Station measures fish food consumption and metabolic rates.

Walleye were held at specific temperatures (5, 10, 15, 20, 25[[ordmasculine]]C) for at least 2 weeks before each experiment. At each temperature, growth and food consumption were measured by holding walleye in individual tanks in a recirculating system at the Illinois Natural History Survey's Kaskaskia Biological Station. The walleye were allowed to feed ad libitum on fathead minnows (Pimephales promelas) for 2 weeks. Minnows were added to every tank each day of the experiment, and minnows that were not eaten were removed. Weight of minnows consumed was determined as weight of minnows added to the tanks minus the weight of the uneaten minnows. Growth was determined by measuring weights and lengths of the walleye at the beginning and end of the experiment after digestion of the minnows was complete. Metabolic experiments were performed in an environmental chamber kept at a constant temperature (5, 10, 15, 20, or 25[[ordmasculine]]C). Rates were monitored for an individual walleye by recording dissolved oxygen levels before and after an hour of rest in an airtight container.

Overall, relative growth, food consumption, and metabolic rates increased for all stocks with increasing temperature. Relative growth (g. g-1. day-1) was reduced at low temperatures (5[[ordmasculine]]C and 10[[ordmasculine]]C) and showed few differences between stocks. At 15[[ordmasculine]]C, the Wisconsin and Canadian populations grew faster. The Missouri population grew the fastest at 20[[ordmasculine]]C, whereas the southern populations grew faster at 25[[ordmasculine]]C. Food consumption rates followed similar patterns as growth across temperatures. Metabolic rates increased for all stocks with increasing temperature but were variable between stocks.

Physiological differences we observed between stocks, as well as other variations, may have strong implications for conservation of walleye stocks and management of introduced stocks. The stocks with the highest growth rate for a particular temperature varied in relation to their evolutionary thermal regimes. Variation in the growth rates we observed between these stocks should be considered before walleye introductions are conducted. Introduced fish should be from stocks with similar thermal regimes to the recipient reservoir. We will eventually develop bioenergetics models that incorporate these stock-specific relationships among temperature, consumption, and growth to predict growth and survival of introduced walleye.

Tracy Galarowicz and David H. Wahl, Center for Aquatic Ecology

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