1. Gonado and Hepato Analysis of the Shovelnose Sturgeon (Scaphirhynchus platorynchus) Population in the Wabash River Austin S. Happel1, Reuben Goforth1, Lindsey Bock1, Jon Amberg1, Tomas Stefanavage2 and Marisol Sepúlveda1, 1Department of Forestry and Natural resources, Purdue University, West Lafayette IN, Indiana Department of Natural Resources, Sugar Ridge FWA, Winslow, IN, 47598
RESULTS
ABSTRACT
Little is known about the sexual demographics of the shovelnose sturgeon (Scaphirhynchus platorynchus) population in the upper Wabash river. We characterized sex ratios and the degree of sexual maturity of 64 shovelnose sturgeon captured in April of 2008 using dissection and histology. Gonads and livers were weighed for calculation of gonado (GSI) and hepato (HSI) somatic indices. Histological sections of gonads were graded in terms of development, whereas liver sections where evaluated in terms of fat content and amount of melanomacrophage centers. Besides GSI, no statistical differences between values for males versus females were found. Interesting findings included the presence of four intersexed males (prevalence of 7%) and two females with eggs infected with Polypodium sp. (prevalence of 16%). Less than 20% of all the fish sampled were females, which could be indicative of a skewed sex ratio for this population. A male- dominated population is not surprising since this population of shovelnose sturgeon continues to be commercially fished to provide roe for the caviar industry.
Twelve Females
Fifty-Two Males
Figure 2. Vitellogenic oocyte showing migration of the germinal vesicle (GV) which is indicative of a female that is ready to spawn. All females in this study were at this developmental stage (FIV). GV
Figure 1.
Mature ovaries (“black eggs”) from an adult female shovelnose sturgeon.
Figure 6.
Testicular tissue from an adult male shovelnose sturgeon.
Figure 7.
Seminiferous tubules filled with mature spermatozoids (S). All males in this study were at this developmental stage (MII.) S
= Normal
= Parasitized
INTRODUCTION
Little is known about the sexual demographics of the shovelnose sturgeon population in the Wabash river basin
Since shovelnose sturgeon are one of a few sturgeon species left open for caviar fisheries, there is much interest in monitoring their populations to ensure that healthy numbers are maintained (Columbo et al., 2007)
Figure 8. Gonado-somatic index (GSI) for males during the study. Mean GSI was 3.66 ± 1.7 % (dotted line). All males were determined to be stage MII.
Figure 3. Gonado-somatic index (GSI) for females during the study. Mean GSI was18.05 ± 3.8 % (dotted line) . All females were determined to be stage FIV. B B A A
In April 2008, 64 shovelnose sturgeon were collected from an electro-shocking boat from a stretch of the Wabash River in Tippecanoe County Indiana along Heron Island
Fish were euthanized using a lethal dose of MS222 and then measured (total length) and weighed
Fish were necropsied and gonads, and livers removed, and weighed for calculation of gonado-somatic (GSI) and hepato-somatic (HSI) indices by dividing the weight of the organ by the body weight of the fish X 100
A piece of gonad and liver was also fixed in 10% buffered formalin for histological evaluation after Hematoxylin and Eosin (H & E) staining
Histological sections were viewed under a compound microscope using a digital camera and representative pictures were collected
Gonads were classified into different stages of maturity using the protocol developed by Bruch et al., (2001) for Lake Sturgeon
Liver samples were classified based on the amount of fat and melanomacrophae centers (MMC) (high, moderate, or low)
Chi-square tests were conducted to compare the different categories of liver condition between genders
METHODS
Figure 9. Hepato-somatic index (HSI) for males during the study (A). Mean HSI was .56 ± % (dotted line). Histological section from a liver of male sturgeon with a low concentration of fat (no empty vacuoles) and high MMC (arrows) (B).
Figure 4. Hepato-somatic index (HSI) for females during the study (A). Mean HSI 1.15 ± 0.2 % (dotted line). Histological section from a liver of a female sturgeon with a high concentration of fat (empty vacuoles) and low MMC (arrows) (B). B A
Figure 10. Macroscopic view of a testes from an intersexed male showing immature follicles (arrow) embedded in testicular tissues (A). Histological sections of same intersex male showing presence of immature oocytes (O) surrounded by seminiferous tubules filled with mature sperm (S) (B and C). A B C O S
Figure 5. Mature oocyte infected with the parasite Polypodium spp. (A). This is the first record of this parasite for this area of North America. Two out of the twelve females sampled were infected (16% prevalence). Life cycle of Polypodium sp. (B).
DISCUSSION
The 0.25 sex ratio found supports the idea that the population studied could be skewed towards males
All males were MII ad all Females were FIV, both stages ready for spawning
The presence of Polypodium spp. constitutes the first record for this parasite in the Wabash River (Raikova, 1979). Its potential impact on the quality of the caviar remains unclear
The cause(s) for the intersex condition remain unknown at this time. Others have attributed it to organochlorine pesticide exposure (Koch, 2006)
No major pathologies were observed in liver tissues
ACKNOWLEDGEMENTS
We wish to thank all the students who helped during the collection and processing of fish in this study.
REFERENCES
Bruch, R. M. et al A field guide for the identification of stages of gonad development in lake sturgeon (Acipenser fulvescens): with note on lake sturgeon reproductive biology and management implications. Sturgeon for Tomorrow, Fond du Lac, WI. 38.
Colombo, R. E., et al Gonadal development and sex-specific demographics of the shovelnose sturgeon in the Middle Mississippi River. Journal of applied Ichthyology. 23:
Koch, B. T., et al Elevated organochlorines in the brain-hypothalamic-pituitay complex of intersexual shovelnose sturgeon. Environmental Toxicology and Chemistry. 25:
Raikova, E. V. et al The parasitic coelenterate, Polypodium Hydriforme USSOV, from the eggs of the American Acipenseriform Polyodon spathula. Journal of Parasitology. 65: