Finfish Blood Sampling

By David Westmark

The St. Petersburg Marine Finfish Biology (Fish Bio) subsection has expanded its toolbox in recent months. Life history research depends on information drawn from examination of many aspects of fish anatomy and physiology. Now, in addition to otoliths, spines/rays, gonads, muscle, guts and scales, two studies within Fish Bio are including analyses of fish blood. In both studies researchers are measuring serum sex steroid levels to expand understanding of reproductive behavior in two economically important fisheries. Estrogen, testosterone, and 11-keto-testosterone are the hormones of interest for these projects.

Results of telemetry work done on common snook on the east coast and in Charlotte Harbor suggest previously unobserved spawning behavior that bucks the conventional wisdom upon which current management strategies are based. Because the sample size of the telemetry work was too small to factor its results into management decisions, a larger investigation was needed. By pairing sex steroid levels in the blood serum with histologically determined reproductive stage of many individual snook of various size classes, a higher resolution picture of the details of snook reproductive behavior should emerge.

The current snook project pursues fish comprising 2 broad categories designated as “non-estuarine” and “estuarine”. Non-estuarine fish (target n =500) are sampled in locations that are considerably distant from known snook spawning aggregation sites. Sampling is conducted from an electrofishing boat in Tampa Bay rivers and tributaries in which salinity is less than 10 ppt. Estuarine fish (target n =500) are cooperatively collected by the Fisheries Independent Monitoring (FIM) lab using haul seines deployed from mullet skiffs at locations closer to snook spawning sites with associated higher salinities.

Field sampling logistics required the Fish Bio snook team to collect blood samples using a somewhat novel approach. Instead of the customary venipuncture technique, blood is pipetted from a deep incision made just posterior to the last gill arch and into the cardiac sinus .

Blood being collected from a common snook via the cardiac cavity

This unconventional method is necessary because blood vessels in dead fish collapse as systemic blood pressure drops too low making venipuncture sampling less successful. To ensure the serum sex steroid levels are not affected by using this technique, blood was drawn from live fish for comparative analysis (n = 20) using traditional venipuncture. Results demonstrate that sex steroid level measurements are valid using either sampling method.


Fish Bio’s Reproductive Dynamics Group is also out for blood… way out! The Madison Swanson marine protected area is the sampling universe for their work targeting grouper species. Plasma sex steroid levels measured in gag grouper may improve understanding of the process underlying the timing and locations of transition from female to male, a key aspect of spawning aggregation dynamics for this closely managed protogynous species.

Blood for this research is drawn from live fish using gill arch venipuncture immediately after hook-and-line capture . Collection tubes are centrifuged aboard the research vessel with the resultant plasma stored in liquid nitrogen for the trip back to the lab at FWRI St. Pete. Blood collection will continue from as many fish as possible until research concludes in 2018.

Collecting blood from the gill arch of a gag grouper

In both studies sampled blood is handled compliant with protocols for subsequent testing using enzyme linked immunosorbent assay (ELISA). Thanks to generous cooperation from Leanne Flewelling and her staff in the Harmful Algal Blooms (HAB) lab, these analyses are conducted on site at FWRI St. Pete at considerably reduced cost. While the Snook and Reproductive Dynamics Teams have perfected their skills on only a handful of ELISA runs, early indications suggest we should stay glued to our chairs for some remarkable results.

While we’re on the subject of new blood, Fish Bio is pleased that Dr. Robert Ellis joined our group a few months ago.
Dr. Ellis earned his masters at Louisiana State University (LSU) modeling gag grouper and marine reserves. His doctoral dissertation work at Florida State University (FSU) examined the way red grouper manipulate habitat. He serves on the Gulf Council Special Reef Fish Scientific & Statistical Committee and recently completed a marine policy fellowship at the NOAA Fisheries Office of Science and Technology in Washington, DC. Robert’s background in applied research, modeling, and exposure to stock assessment and policy will be a great fit in the Fish Bio program. Here’s an article from Florida Sea Grant about Bob and some of his recent work.