1. Why is there a difference in sex ratio between hatchery and wild steelhead?
Neil Thompson1, Kassi Cole2, Laura McMahon1, Melanie Marine1, Lyle Curtis and Mike Blouin1
1 Department of Zoology, Oregon State University
2 Department of Zoology, University of Hawaii

2. Hood River steelhead

3. Hood River Sex Ratio 1.07 Average sex ratio over all run years
Wild
Wild sex ratio
Hatchery
Hatchery sex ratio
Run Year
# Male
# Female
(Females per male)
1991
290
434
1.50
182
111
0.61
1992
159
260
1.64 99
133
1.34
1993
132
264
2.00 85
0.86
1994
100
104
1.04 56 57
1.02
1995
112
167
1.49
172
106
0.62
1996
118
175
1.48
334
301
0.90
1997 88
137
1.56
220
1.28
1998
188
1.68
156
166
1.06
1999
355
567
1.60
151
150
0.99
2000
372
645
1.73
533
415
0.78
2001
406
648
670
527
0.79
2002
485
1.87
231
366
1.58
2003
245
386
506
497
0.98
2004
160
208
1.30
238
297
1.25
2005
300
1.44
461
396
2006
186
313
267
2007
116
235
2.03 72
122
1.69
2008 81
140
202
190
0.94
2009
255
411
1.61
772
1076
1.39
Average sex ratio over all run years
1.07
Wild population always female biased
Hatchery population 50:50 ratio , 9 years female biased, 10 years male biased

4. Hood River Sex Ratio
Wild population: ALL 19 years female biased
Average ratio - 61:39
Hatchery population: 9 years female biased
Average ratio - 51:49
Wild population always female biased
Hatchery population 50:50 ratio , 9 years female biased, 10 years male biased
Question: Why is there a difference in sex ratio between wild and hatchery populations?

5. Potential explanations
Lower rates of residency in male hatchery fish
Selection against hatchery females, in the hatchery or at sea
Sex reversal of chromosomally XX females into phenotypic males

6. Potential explanations
Lower rates of residency in male hatchery fish
Selection against hatchery females, in the hatchery or at sea
Sex reversal of chromosomally XX females into phenotypic males

7. Sex determination in steelhead
Y chromosome = male
No Y chromosome = female

8. Mechanism of Sex Reversal
Aromatase enzyme
Converts testosterone to estrogen
High temperature inhibits aromatase

9. Mechanism of Sex Reversal
Aromatase enzyme
Converts testosterone to estrogen
High temperature inhibits aromatase
Expect chromosomal females develop testes

10. Why Aromatase? Spawned in Parkdale, Oregon
Reared at Oak Springs on Deschutes R.
Deschutes warmer than Hood River

11. Research question
Does the chromosomal gender match the phenotypic gender in Hood River steelhead?
If not, what % is non-matching?
What direction is mismatch?

12. Research question
Does the chromosomal gender match the phenotypic gender in Hood River steelhead?
If not, what % is non-matching?
What direction is mismatch?
Does the sex ratio in the hatchery population change from juvenile release to adult return?

13. Methods - Adults Adults sampled at Powerdale dam (1991-2009)
Gender, origin, fin clip taken by ODFW
Random 96 individuals per run type & sex
Total 384 adult samples
Wild and Hatchery origin

14. Methods - Juveniles
Juveniles produced following Hood River Production Program protocols
Sampled at 1 year of age
Fin clip & floy tagged
Bodies preserved in formalin
Gonad inspected by stereomicroscopy
Fish type, family, spawn date

15. Chromosomal gender OmyY1 marker - gender marker
4% non-concordance rate
Male band
Positive reaction band

16. Phenotypic gender
Adults:
ODFW staff visually sexed powerdale

17. Phenotypic gender Adults: 1 year olds:
ODFW staff visually sexed powerdale
1 year olds:
Visually sexed gonads
Male, female or unknown

18. Research question
Does the chromosomal gender match the phenotypic gender in Hood River steelhead?
If not, what % is non-matching?
Mismatch = sex reversal
Test for non 50:50 sex ratio
Chi-square test

19. Results - Adults 341 successful reactions
7 fish mismatched (2.1 % non-concordance)
Male-to-female and female-to-male mismatch
Chromosomal
Run
Gender
% Non-concordance
Winter
Male
2.27
Female
1.15
Summer
1.28
3.41

20. Results - Juveniles 173 successful reactions
6 fish mismatched (3.5 % non-concordance)
Male-to-female and female-to-male mismatch
Juvenile ID
Spawn Date
Family ID
Fish Type 2
4/20/2010
2821x2796 HH 3
5/24/2010
382x477 WW 29
5/10/2010
2764x2783 44
2812x2761 62
5/17/2010
458x2804 WH
223
2774x383 HW

21. Overall Results Adults No evidence for sex reversal
Mismatches in both directions
Rate not above published non-concordance rate
ODFW staff VERY good at visually identifying gender – both run types

22. Overall Results Adults Juveniles No evidence for sex reversal
Mismatches in both directions
Non-concordance rate below published rate
Mismatches from 6 different families, 4 spawn dates and 4 fish types

23. Potential explanations
Lower rates of residency in male hatchery fish
Selection against hatchery females, in the hatchery or at sea
Sex reversal of chromosomally XX females into phenotypic males

24. Juvenile sex ratio at release
# Male
# Female
Chromosomal 85 88
Phenotypic 87 86
*Not different from 50:50 ratio*
Chi-square p-values of 0.82 & 0.94

25. Juvenile sex ratio at release
# Male
# Female
Chromosomal 85 88
Phenotypic 87 86
*Not different from 50:50 ratio*
Chi-square p-values of 0.82 & 0.94
50:50 at release and at return to the dam
No selection against females in hatchery or at sea!

26. Potential explanations
Lower rates of residency in male hatchery fish
Selection against hatchery females, in the hatchery or at sea
Sex reversal of chromosomally XX females into phenotypic males

27. Potential explanations
Lower rates of residency in male hatchery fish
Christie et al Molecular Ecology

28. Thank You! Jim Gidley & Albert Santos Lyle Curtis & staff Blouin lab
Parkdale fish facility
Lyle Curtis & staff
Oak Springs hatchery
Blouin lab