Effects of selected hormones and male cohorts on
final oocyte maturation, ovulation, and steroid
production in walleye (Stizostedion vitreum)
Terence P. Barry *, Jeffrey A. Malison, Anita F. Lapp, Lynne
15 June 1995
A series of in vivo and in vitro experiments were conducted to evaluate the effects of selected
hormones and male cohorts on oocyte maturation and ovulation in walleye captured from the wild.
In one experiment conducted 2 weeks prior to the normal spawning season, single intramuscular
injections of human chorionicgonadotropin (hCG, 500 IU kg- ‘) and des-Gly”’ [D-Ala”] LHRHethylamide ( LHRHa, 100 pg kg ’ ) stimulated final oocyte maturation and ovulation. LHRHa induced
oocyte maturation faster than hCG. The presence of spermiating males had a slight stimulatory effect
on oocyte maturation in non-injected fish, but did not potentiate the effects of LHRHa. In a second
experiment conducted 3 weeks prior to normalspawning, hCG (500 IU kg-‘), LHRHa ( 100 pg
kg ’ ), and 17,20-P ( 100 pg kg- ’ ) all induced final oocyte maturation. In this experiment, however,
hCG was more effective than LHRHa, and there was no male cohort effect. In maturing females,
oestradiol-17P levels declined, and testosterone levels increased transiently prior to final oocyte
maturation and ovulation. Levels of17cu,20P-dihydroxy-4-pregnen-3-one
( 17.20-P) were significantly elevated 2 and 3 days prior to ovulation. Cortisol levels were high (50-l 00 ng ml ’ ) in newly
captured fish and remained elevated during the experimental period. No control fish in either experiment underwent final oocyte maturation. These findings suggest that capture and confinement stress
may inhibit oocyte maturation in walleye.
In vitro,human chorionic gonadotropin (hCG) was a potent inducer of final oocyte maturation
whereas LHRHa had no effect. Of various steroids tested in vitro, 17,20-P and 17a,20P,21-trihydroxy4-pregnen-3-one were the two most effective inducers of final oocyte maturation and ovulation, and
the lowest dose of 17,20-P tested (0.01 ng ml- ‘) was a consistent and potent inducer of final oocyte
maturation. Thesedata, together with our in vivo results, support the hypothesis that 17,20-P may be
steroid in walleye. Cortisol, alone or in combination with hCG, had no effect
* Corresponding author.
Elsevier Science B.V. All rights reserved
T.P. Barry et al. /Aquaculture 138 (1995) 331-347
on oocytematuration or ovulation in vitro, indicating that any negative effects of cortisol on oocyte
maturation in walleye probably occurs at higher levels of the hypothalamic-pituitary-gonadal axis.
The walleye, Stizostedion uitreum, is one of the most important commercial and recreational fish species in the northern U.S. and Canada. Over one billion walleye fry and
fingerlings arestocked annually in North America for resource enhancement (Conover,
1986). There is also a growing commercial walleye aquaculture industry which primarily
produces fingerlings for stocking public and private lakes, but which has potential to
eventually supply larger food-sized fish for retail markets and restaurants (see Coolwater
Workshop, 1992). Currently, both public and private walleyehatcheries rely almost exclusively on eggs taken from ovulated fish captured from the wild. For commercial walleye
aquaculture to develop and expand, methods are needed for maturing and spawning walleye
held in captivity.
Wild female walleye captured during the spawning season will not normally spawn if
captured prior to ovulation (Pankhurst et al., 1986). These fish can be induced to ovulate...