Date of Award

Spring 5-2015

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Chair

Andrew Evans

Committee Chair Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 2

Reginald Blaylock

Committee Member 2 Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 3

Chet Rakocinski

Committee Member 3 Department

Coastal Sciences, Gulf Coast Research Laboratory

Abstract

Alteration of habitat associated with coastal development and increased demand for food and recreation can result in the depletion of fisheries resources such as the Spotted Seatrout (Cynoscion nebulosus), the Gulf of Mexico’s most popular recreational fish. Stock enhancement, or the release of cultured fish to supplement wild populations, is one potential tool for managing important fisheries resources. Although much effort has gone into marine stock enhancement, the effectiveness of stocking is not well established, and techniques for ensuring success have not been developed. Although the basic biology of the Spotted Seatrout is well known, comparatively little is known about its physiology, including how it responds to physical stressors associated with handling, transport, and release procedures. My research focused on the impacts of these physical stressors on the stress response (i.e., cortisol production), survival, condition, and inferred growth of Spotted Seatrout upon release. In Chapter II, I present a two-part study on the stress response of Spotted Seatrout exposed to the stressors associated with the stock enhancement process. I assessed whole body cortisol concentrations in both 48- and 80-day post-hatch (dph) fish during real time stock enhancement processes such as netting/handling, tagging, transport, and release, followed by a 30-day field experiment designed to examine the impacts of stock enhancement procedures on post-release growth, Fulton’s Condition Factor (K), and survival. Cortisol in 48-dph fish nearly doubled 15 minutes post-net (from 2,413 pg/g in controls), increased to a peak of almost sevenfold in the immediate post-transport treatment, and then decreased by approximately 50% from the peak in 60 minute post-transport fish just prior to release. In 80-dph fish, cortisol initially increased by about 15% 30 minutes post-tag (from 799 pg/g in controls), peaked at threefold by 120 minutes post-tag, and decreased about 15% from the peak through the transport processes before spiking slightly just prior to release. Even though 80-dph fish experienced more stressors than their 48-dph counterparts, including tagging, they exhibited a lower cortisol concentration throughout, perhaps indicative of down-regulation of the Hypothalamic-Pituitary-Interrenal (HPI) axis. For 48-dph fish in the cage study, survival was high and similar in control and experimental groups, but experimental fish were shorter, lighter, and of lower K than control fish. For 80-dph fish, fewer experimental fish survived than control fish, and those that survived were of lower K than fish in the control group. In Chapter III I present a novel cortisol extraction procedure for use in intermediate sized fishes (i.e., fish that are too small to provide a blood sample adequate for plasma extraction, yet too large to efficiently conduct whole-body homogenization). Assay precision and accuracy was comparable to both plasma and whole-body extraction procedures. This extraction procedure allows for smaller portions of a larger fish to be sampled for cortisol, while at the same time, eliminating any potential interfering lipids that may otherwise be extracted along with cortisol using whole-body extraction procedures. Intra-assay percent CV was 8.54%. Average recovery of spiked samples was 102%. This extraction procedure was therefore an effective mechanism for measuring cortisol in fish not amenable to plasma or whole-body extraction procedures. In conclusion, this study suggests that younger, untagged fish have higher post-release survival than those grown to the size needed for insertion of a coded-wire tag. These data also suggest that effects of the tagging procedure need further investigation.

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