Seasonal variations in sperm production and sperm quality in male winter flounder, Pleuronectes americanus: the effects of hypophysectomy, pituitary replacement therapy, and GnRH-A treatment
B. Shangguan et Lw. Crim, Seasonal variations in sperm production and sperm quality in male winter flounder, Pleuronectes americanus: the effects of hypophysectomy, pituitary replacement therapy, and GnRH-A treatment, MARINE BIOL, 134(1), 1999, pp. 19-27
The pattern of sperm release and changes in sperm quality were investigated
throughout the normal spawning season of male winter flounder, Pleuronecte
s americanus (Walbaum), caught in Conception Bay, Newfoundland, Canada in A
pril and November 1994. In addition, the impact of hormonal manipulation on
sperm production and sperm quality was examined through gonadotropin-relea
sing hormone analogue (GnRH-A) treatment, hypophysectomy, and pituitary ext
ract injection - pituitary replacement therapy (PRT). While a lengthy perio
d of spermiation, lasting similar to 6 months (December to July), can be de
tected in some males, the major period for sperm release occurred in May to
July in the summer spawning season. The spawning period started with peak
levels of plasma testosterone (T) and 11 ketotestosterone (11-KT). By late
July sperm production fell rapidly along with a notable deterioration in sp
erm motility. While GnRH-A treatment advanced the period of sperm release,
and the milt became diluted and increased in volume, the treatment did not
increase total sperm output over the spawning season. In hypophysectomized
male flounder, by contrast, milt was more concentrated and sperm production
declined along with reduced plasma androgen levels during the spawning sea
son. Increased plasma T and 11-KT levels in hypophysectomized males followe
d PRT in December and January. Moreover, PRT appeared to be responsible for
advancement of spermiation in a large number of prespawning males, which r
eleased an increased amount of milt. Finally, these studies indicated that
both sperm motility and egg fertilization rates remained unchanged after th
ese hormonal treatments.