Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


A comprehensive understanding of migration dynamics, within-estuary behaviors and physiological tolerances of fish is needed to assess and predict future responses of fish to environmental disturbance and to protect habitat necessary for growth and survival. This study adds to current knowledge of summer flounder (Paralichthys dentatus) responses to environmental conditions by (1) examining migration and within-estuarine behaviors of adult summer flounder and (2) establishing summer flounder metabolic requirements and cardiorespiratory responses to variations in hypoxia and temperature. To elucidate use of a southern mid-Atlantic Bight estuary by adult summer flounder, the movements of 45 fish were monitored using acoustic telemetry within a seaside lagoon along Virginia‟s Eastern Shore. Mean residence time in this region was 1.5 times greater than previously reported for this species. The majority of fish remained within the estuary until mid-October, although some fish dispersed from the system earlier, and some temporarily exited and re-entered the system before final dispersal. Migration into or out of the system most closely followed seasonal changes in mean water temperature, but photoperiod and other factors may also play a role. Fish resided primarily in the deeper regions of the lagoon system, where strong currents preclude the development of suboptimal conditions such as hypoxia. Summer flounder also generally exhibited low levels of large-scale activity (e.g., 100s of meters). Variations in the migratory and within-estuary behaviors indicate that individual fish use different strategies to maximize food and habitat resources. Additional research is necessary to identify preferences and behaviors of summer flounder within estuaries and along the inner continental shelf and to relate these to prey distribution. To provide a metabolic framework for understanding how summer flounder respond to hypoxia, stopflow respirometry was used to measure changes in resting metabolic rate, oxygen extraction, gill ventilation and heart rate during progressive hypoxia at an acclimation temperature (22°C) and after an acute increase to 30°C. Summer flounder experience a 6-fold increase in gill ventilation while maintaining oxygen extraction above 50%. However, the critical oxygen saturation increased significantly from 27% at 22°C to 39% at 30°C, suggesting a lower tolerance to hypoxia after exposure to an acute increase in temperature. In addition, fish subjected to 30°C were unable to increase gill ventilation to as great an extent as at 22°C. At both temperatures, significant bradycardia was only observed when oxygen levels decreased to levels below critical oxygen saturation. Due to their ability to maintain aerobic metabolism in low oxygen conditions, summer flounder are not likely to avoid hypoxic conditions to maintain aerobic metabolism in the wild. However, exposure to hypoxia can decrease aerobic scope and consequently affect somatic and gonadal growth rates. Additional studies specifically examining the effects of hypoxia and temperature on aerobic scope are necessary to fully understand the effects of variable environmental conditions on growth and reproduction in this species.



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