SEASONAL FLUCTUATIONS IN PLASMA STEROID CONCENTRATIONS, EGG DIAMETERS, AND 
GONADAL STAGE IN SHOVELNOSE STURGEON

Authors: Michael T. Stahl, Anita M. Kelly, Gregory W. Whitledge
Department of Zoology, Fisheries and Illinois Aquaculture Center, Southern 
Illinois University, Carbondale, IL 62901.

Fishing pressure on shovelnose sturgeon Scaphirhynchus platorynchus in the 
Mississippi River drainage basin has increased substantially as a result of 
the importation ban of beluga sturgeon caviar into the U.S. and high caviar 
prices.  Knowledge of seasonal changes in reproductive status would be 
valuable for shovelnose sturgeon management, but temporal variation in blood 
steroids and vitellogenin (VTG; an egg protein precursor) have not been 
examined in middle Mississippi River shovelnose sturgeon.  The objective of 
this study was to determine whether egg diameters and blood steroid and VTG 
concentrations differ among months and fish ages for shovelnose sturgeon 
captured from the middle Mississippi River.  Shovelnose sturgeons were 
harvested monthly from the middle Mississippi River between river miles 77 
and 125 from October 2005 to February 2007.  Physical analyses of harvested 
sturgeon consisted of measuring length and weight, collecting blood and 
female gonad samples, and pectoral spines for aging.  Plasma steroid 
concentrations (17ß-estradiol (E2) and testostosterone (T)) were determined 
by radioimmunoassay (RIA), while VTG concentrations were determined using 
ELISA.  Oocyte diameter and number were recorded from gonad sub-samples and 
polarization indices were calculated for mature black eggs.  Mean fecundity 
for black egg females was 20277 ± 7570 eggs and increased with fish age.  
Oocyte diameters increased with reproductive stage, fish size, and age.  
Shovelnose sturgeon = age 8 had uniformly low hormone concentrations, while 
fish = age 9 exhibited a broad range of blood steroid concentrations, 
indicating that maturity likely occurs at around age 9.  Plasma estradiol and 
testosterone concentrations peaked in April and October, while plasma VTG 
concentrations peaked during March and September.  These results are 
consistent with previous studies which indicated that female sturgeon may 
spawn during spring and fall in the middle Mississippi River.  

Keywords: Mississippi River, Shovelnose Sturgeon, Sex Hormones, Vitellogenin, 
Oocytes


Presenter
Name: Michael T. Stahl
Address: Life Science II, Rm 173, 1125 Lincoln Drive, Carbondale, IL 62901
Phone number: 618-453-2608  Fax number: 618-453-6095
Email address: mtstahl@siu.edu

Poster presentation requested; willing to convert to presentation format 
(PowerPoint)
Student presenter
Only need standard space for standard size poster