Nonlethal Health Assessments of Fish: Using Endocrinology Techniques to Study Stress and Sex Hormones As a Function of Health in Red Drum

New methods are being sought to assess the health and well-being of wildlife as indicators of ecosystem health or to quantify the robustness of animals that are representative of the broader population. In Florida, the health of manatee, dolphin, and alligator populations on both coasts is assessed each year, and the results are used to monitor these populations and indicate potential threats (i.e. contaminants and infectious disease) to humans. These assessments are performed without endangering the animals. In contrast, nonlethal methods of catching and handling fish for blood sampling are not well developed. Improper handling can injure or kill fish and bias the results of the sampling. 

Free-ranging red drum (Sciaenops ocellatus) in the Merritt Island National Wildlife Refuge (MINWR) were studied to develop a nonlethal protocol to define health and baseline blood values for stress and sex hormones of the population. Surrounding Kennedy Space Center, MINWR is the oldest protected no-take fisheries reserve in the United States.

Fish Collection Techniques

Red drum were caught by hook and line and were landed within 3 minutes of initial strike. Blood was collected from the couverian artery within 7 minutes. Angling was faster than using seine nets or trammel nets, methods that would have left the fish struggling in a net for more than 15 minutes before a blood sample could have been obtained. Instead of being anesthetized, the fish were held lightly and briefly on a v‑board for blood collection. This technique worked well, and the fish recovered quickly after they were released into the lagoon. 

Blood Plasma for EIA and RIA Analysis

Plasma was evaluated by enzyme immunoassay (EIA) for cortisol, 11‑ketotestosterone and radioimmunoassay (RIA) for 17β‑estradiol, and lab absorbance assay for glucose. Values for sex and stress hormones were compared by sex and temporal analysis. 

Conclusions

1. Blood collection via the gill site was successful and superior to previous methods.
2. No anesthesia was necessary to handle large wild fish caught by hook and line.
3. The recapture of red drum proves that nonlethal health sampling has long-term benefits.
4. KSC serves as an important reserve for healthy spawning adult red drum.

These techniques will be further developed as part of a health assessment protocol on red drum in the study area, and ultimately the data will be compared with that of other heavily fished populations.