Preliminary Investigation into Developing the Use of Swabs for Skin Cortisol Analysis for the Ocean Sunfish (Mola mola)

Abstract

The ocean sunfish (mola; Mola mola) is the heaviest bony fish in the world. This slow-moving fish often is injured by fishing boats that use drift gillnets attributing to its listing as Vulnerable by the IUCN. The Monterey Bay Aquarium (Monterey, CA, USA) has a program that brings in smaller molas from the ocean and acclimates them for an exhibit. When they grow too large for the million-gallon Open Seas exhibit, they are returned to Monterey Bay through a “reverse” acclimatization. Our overall goal was to use skin swabs to evaluate mola stress physiology to better understand the effects of this program. Our objectives were to validate this non-invasive method by taking opportunistic swabs throughout acclimatization and during stressful events. We swabbed each individual (n = 12) in three different body locations. Swabs were analyzed using a cortisol enzyme immunoassay. We averaged the three swabs and examined the absolute change of cortisol from the first taken upon handling to during treatments and the different acclimation stages. We considered elevated cortisol concentrations to be ≥1.5-fold higher than the first sample. Overall, mean (±SEM) cortisol varied among individuals (564.2 ± 191.5 pg/mL swab (range, 18.3–7012.0 pg/mL swab). The majority (four of six) of molas swabbed within the first week or month had elevated skin cortisol compared to their first sample. All seven molas that were being treated for an injury or illness had elevated skin cortisol (range, 1.7- to 127.6-fold higher) compared to their post-acclimation sample. This is the first step in validating the use of non-invasive skin swabs for glucocorticoid analysis in the mola. Further biochemical analysis is needed to determine the specific steroids that are being measured.

Exploring the Effect of Age on the Reproductive and Stress Physiology of Octopus bimaculoides Using Dermal Hormones

“…We consider a value less than that to indicate little response to the stress test. While other researchers have validated the use of dermal swabs to measure changes in glucocorticoids of other aquatic species, such as Mola mola, using a 1.5-fold increase or higher as an indicator of a stress response [35], we considered the 2-fold (or 200%) increase to be indicative of a response to a stressor since our understanding of cephalopod stress physiology is limited. Regardless, we report the increase above baseline and invite future consideration of appropriate cut-offs for a demonstrable increase in response to a stressor.…”

“…We used a previously described cortisol EIA to measure cortisol concentrations with dermal swabs [35,36]. Briefly, the polyclonal cortisol antiserum (R4866) and horseradish peroxidase (HRP), provided by C. Munro (University of California, Davis, CA, USA), were used and diluted to 1:375,000 and 1:200,000, respectively, in a 96-well plate that was coated with goat anti-rabbit antibody (1:1000, Arbor Assay, Ann Arbor, MI, USA).…”

“…Collecting mucus via swabs from the octopus' skin surface may provide a noninvasive alternative for measuring hormones. Dermal swabs have been used previously in fish [31][32][33][34][35][36] and amphibians [36] and were recently validated for use with three cephalopod species, Euprymna berryi, Sepia bandensis, and Octopus chierchaie, [28].…”