Israt Jahan

Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2018

Thesis Director

Anabela Maia

Thesis Committee Member

Robert E. Colombo

Thesis Committee Member

Britto P. Nathan

Abstract

Fishes have evolved physiologically to live within a specific range of environmental variation and existence outside of that range can be stressful or fatal. These ranges can coincide for fishes that evolved in similar habitats. This study investigates physiological processes limiting thermal tolerance, specifically how changes in water temperature affect the swimming energetics and muscle mechanics in largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). I focused on the impact of temperature change at the muscle level in these two species and the capacity to adapt to rapid changes in the environment. Fish were housed at 20°C and then tested in a recirculating flow tank 2 body length (BL)/sec at 16°C, 20°C and 22°C while measuring water oxygen consumption as a proxy of metabolism. Fish were fasted for at least 24 hours and acclimatized for 2 hours prior each trial. All temperatures were controlled by chiller and heater. Fish were also implanted with bipolar electrodes to record muscle activity using electromyography (EMG) standard techniques. Mass corrected oxygen consumption was different between fish ran at the three different temperatures. Overall, metabolic rate was higher at higher temperatures. Mass corrected oxygen consumption was influenced not only by temperature but also by both species and species and temperature interactions. Active metabolic rate was higher in largemouth bass than in bluegill at 16°C and 20°C. However, at 22°C bluegill had almost 1 .35- fold higher active metabolic rate. The temperature quotient Q10 is the measure of temperature sensitivity of a biological system and for current study it was calculated from l 6°C to 20°C and 22°C for both species to measure how the physiology is affected by increase in temperature. Calculated Q10 at 2 BL/s was 1 .43 for largemouth bass and 7.3 1 for bluegill (16-22°C). At higher temperatures oxygen consumption increases in fish while oxygen content decreases in water due to a lower saturation pressure, making oxygen a clear limiting factor. This is likely to affect health and growth of individuals, especially when mobility to a lower temperature environment is not possible. While swimming at the same speed (2BL/s), electromyography recordings showed swimming characterized by activation of the musculature. With increased temperature fish start recruiting more red muscles and white muscle by showing greater magnitude and longer duration of muscle activation. Fish are thus capable of changing muscle mechanics to adapt to change in temperature, although bluegill and largemouth bass use distinct strategies. Largemouth bass has less or no activity of axial red muscles at 22°C while bluegill successfully recruit red muscles at all three temperatures. Using more white muscles at higher temperature may lead largemouth bass to an additional demand of oxygen consumption after swimming at higher temperature to maintain functional balance.

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