Spermatogenesis and related
plasma androgen levels in Atlantic halibut (Hippoglossus hippoglossus
L.)
F.-A.
Weltzien, G.L. Taranger, Ø. Karlsen, B. Norberg-2002
Comparative Biochemistry and Physiology - Part A:
Molecular and Integrative Physiology, 132(3): 567-575
Abstract:
Spermatogenesis in male Atlantic halibut (Hippoglossus
hippoglossus L.) was investigated by sampling blood plasma and
testicular tissue from 15-39-month-old fish. The experiment covered a period
in which all fish reached puberty and completed sexual maturation at least
once. The germinal compartment in Atlantic halibut testis appears to be
organized in branching lobules of the unrestricted spermatogonial type,
because spermatocysts with spermatogonia were found throughout the testis.
Spermatogenesis was characterized histologically, and staged according to
the most advanced type of germ cell present: spermatogonia (Stage I),
spermatogonia and spermatocytes (Stage II), spermatogonia, spermatocytes and
spermatids (Stage III), spermatogonia, spermatocytes, spermatids and
spermatozoa (Stage IV), and regressing testis (Stage V). Three phases could
be distinguished: first, an initial phase with low levels of circulating
testosterone (T; quantified by RIA) and 11-ketotestosterone (11-KT;
quantified by ELISA), spermatogonial proliferation, and subsequently the
initiation of meiosis marked by the formation of spermatocytes (Stage I and
II). Secondly, a phase with increasing T and 11-KT levels and with haploid
germ cells including spermatozoa present in the testis (Stage III and IV).
Thirdly, a phase with low T and 11-KT levels and a regressing testis with
Sertoli cells displaying signs of phagocytotic activity (Stage V).
Circulating levels of 11-KT were at least four-fold higher than those of T
during all stages of spermatogenesis. Increasing plasma levels of T and
11-KT were associated with increasing testicular mass throughout the
reproductive cycle. The absolute level of, or the relation between, testis
growth and circulating androgens were not significantly different in first
time spawners compared to fish that underwent their second spawning season.
These results provide reference levels for Atlantic halibut spermatogenesis.