Enhancement of spermiation
in European sea bass (Dicentrarchus labrax) at the end of the
reproductive season using GnRHa implants
S. Rainis, C.C. Mylonas, Y. Kyriakou, P.
Divanach-2003
Aquaculture, 219(4): 873-890
Abstract:
Spermiating European sea bass (Dicentrarchus
labrax) were treated at the end of the reproductive period (22 February
2002) with implants of gonadotropin-releasing hormone agonist (GnRHa), in
order to examine their potential in enhancing expressible milt volume, sperm
quality and in vitro fertilization success. The GnRHa implants at all doses
(20, 40 and 80 µg GnRHa kg-1 body weight [bw]) stimulated a
significantly higher production of milt compared to controls over a 27-day
period, increasing total volume from 0.5 to 2.2 ml kg-1 sample
time-1. No differences in milt production were observed among the
three GnRHa doses. Histological evaluation of the testes indicated that, by
day 21, control fish had entered into gonadal regression, containing almost
exclusively spermatogonia. At the same time, testes from GnRHa-implanted
fish still contained large numbers of spermatozoa in the testes, indicating
that spermiation was still underway. Sperm density varied between 7.4 and
14.4×1010 spermatozoa ml-1, but remained unchanged in
response to GnRHa implantation. Sperm motility was high at the beginning of
the experiment (92–100%) and decreased significantly by day 27 (32–55%),
whereas motility duration was unchanged (0.9–1.2 min). Neither sperm
motility nor motility duration was affected by the GnRHa treatment. Finally,
fertilization success was high (40–80%) and not significantly different in
response to GnRHa implantation. These results demonstrate that GnRHa
implants are effective at increasing milt production at the end of the
spermiation period, maintaining high sperm density and not affecting, either
positively or negatively, sperm quality and fertilization capacity.
(Institute of Marine Biology of Crete, P.O. Box 2214,
Iraklion, Crete 71003, Greece, e-mail of C.C. Mylonas: mylonas@imbc.gr)