Vol. 275, Issue 6, R1793-R1802, December 1998
Sex steroids and the initiation of puberty in male African
catfish (Clarias
gariepinus)
J. Eduardo B.
Cavaco1,
Cécile
Vilrokx1,
Vance
L.
Trudeau2,
Rüdiger
W.
Schulz1, and
Henk J. T.
Goos1
1 Utrecht University, Faculty
of Biology, Department of Experimental Zoology, Research Group for
Comparative Endocrinology, 3584 CH Utrecht, The Netherlands; and
2 University of Aberdeen,
Department of Zoology, Aberdeen AB24 2TZ, United Kingdom
The
effects of sex steroids on spermatogenesis and testicular androgen
secretion were studied in juvenile (spermatogonia present in testes)
African catfish. Fish were implanted with Silastic pellets containing
11-ketotestosterone (KT), 11
-hydroxyandrostenedione (OHA), androstenetrione (OA), androstenedione (A),
testosterone (T), 5
-dihydrotestosterone (DHT), or estradiol-17
(E2). Control groups received
steroid-free pellets. Two weeks later, testis tissue fragments were
incubated with African catfish luteinizing hormone (LH) and the amount
of OHA secreted in vitro (the main androgen produced by African catfish
testes) was quantified. Tissue fragments were then fixed for
histological analysis of spermatogenesis. Treatment with KT, OHA, and
OA stimulated testicular growth and spermatogenesis (spermatocytes and
spermatids were found), whereas T, DHT, A, or
E2 had no such effects. All
steroids, except for DHT and E2,
reduced OHA secretion in the absence and presence of LH to ~10% of
the control values. Previous studies have shown that KT, OHA, and OA
have little effect on circulating LH levels in juvenile male African
catfish, so that these androgens probably had direct effects on the
testis. Inasmuch as OHA, OA, and KT have largely similar effects and
because OHA and OA are converted to KT in vivo, we suggest that KT is
physiologically the most relevant androgen for the initiation of
spermatogenesis in African catfish.
teleost fish; juvenile males; steroid hormones; secondary sexual
characteristics; testicular androgen secretion in vitro
