This study sought to determine the lower size limit at which histological examination can reliably determine sex in northern pike. Samples of juvenile pike ranging from 45-90mm were collected and sections of their peritoneal cavity were examined microscopically. The study found that sex could be differentiated as early as 48mm (30-70 days old), as female gonads have two attachment sites while male gonads have one. Future work will aim to determine the size at sexual differentiation and investigate environmental factors influencing sex ratios in the species.

1. Sex Determination and Gonadal Development
in St. Lawrence River Northern Pike
Kelly Huffman, Christopher M. Whipps, and John M. Farrell
Thousand Islands Biological Station – SUNY-ESF State University of New York College of Environmental Science and Forestry
Introduction
• Histological techniques have been used to determine sex for Northern Pike at 47
days or 70-80mm (Luczynski et al. 2003).
• We are seeking to determine lower limit of histological determination of gender
in Northern Pike.
• Samples of juvenile pike from 45-90mm were collected (Fig. 1).
• Cross sections were cut through peritoneal cavity (Fig. 3 and 4) and embedded in
paraffin and mounted as a slide.
Results
www.esf.edu/tibs
• Northern Pike gender can be easily determined in mature fish by the presence of eggs
and milt.
• Gender determination at early stages of development (e.g., egg and larval) presents a
challenge because gonads are not identifiable.
• This precludes any investigation of sex linked biological processes.
• A histological method to reliably determine gender at early life stages is needed to
further investigate sex determination.
Methods
References
Luczynski, M. J., Demska-zakes, K., Dabrowski, K., & Luczynski, M. (2003). Masculinization of Gynogenetic
Northern Pike Juveniles Using 17 α -Methyltestosterone. North American Journal of Aquaculture, 65(3),
255–259.
Future Work
• Determine gender in early life stages of Northern Pike to calculate sex ratios.
• Determine size/age of sexual differentiation based on histological examination of
gonadal duct development in fish smaller than 48mm and larger than 12mm.
• Investigate environmental factors with potential to affect the sex ratio in Northern
Pike, specifically what may be associated with the higher proportion of females
observed in the St. Lawrence River tributaries.
Figure 1: Juvenile Northern Pike (~75mm)
Figure 3: Cutting cross sections
of Northern Pike
Figure 4: Cross sections in cassettes
for processing into slides
• During the annual spawning survey in St. Lawrence River tributaries, Northern Pike
gender is determined. Only Northern Pike extruding gametes or hard prespawn
females are included. (Fig. 2)
• Average over 15 years 67.3% Female
• Average over 10 years 64.6% Female
Sex Ratio
Figure 2: Sex ratio trends in spawning tributaries in the St. Lawrence River
during March and April from ripe pike of both genders and hard females.
40
45
50
55
60
65
70
75
80
85
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
PercentFemale
Year
Research Questions
The ability to determine gender of Northern Pike at any life stage will enable us to
explore the possible mechanisms leading to sex ratio imbalance. This research is
designed to address these central questions:
• At what life stage or size does sex differentiation occur?
• What mechanism or mechanisms are responsible for sex determination?
Figure 5: Northern Pike egg Figure 6: Northern Pike larva
• Through histological observation, pike gender was differentiated in fish as small as
48mm (30-70 days old).
• Female gonads have two attachment sites (Fig. 7 and 9) while male gonads have only
one attachment site (Fig. 8).
• 14 day old pike larvae at ~12mm were also examined however the gonadal ducts were
not yet visibly developed.
Figure 7: Gonad of 77mm female pike
Figure 8: Gonad of 54mm male pike Figure 9: Gonad of 70mm female pike
• This work is funded by Federal Aid in Sportfish Restoration Grant number F-61-R
Study 9 administered by the New York State Department of Environmental
Conservation. Additional funding provided by American Wildlife Conservation
Foundation.
• Jacob Runner, Brandy Brown, Andrew Miano, and Ben Amos
• Committee member: Gordon Paterson (SUNY-ESF)
Acknowledgements
Female
2 attachment sites
Male
1 attachment site