Relationship between ovarian
development and serum levels of gonadal steroid hormones, and induction of
oocyte maturation and ovulation in the cultured female Korean spotted sea
bass Lateolabrax maculatus (Jeom-nong-eo)
W.-K.
Lee, S.-W. Yang-2002
Aquaculture, 207(1-2): 169-183
Abstract:
Gonad and blood samples were taken from the cultured
female Korean spotted sea bass Lateolabrax maculatus from August to
November in 1998 and 1999. Under net cage culture, the female fish did not
mature and spawn, but spermiation in males occurred spontaneously in the
natural spawning season. Gonadosomatic index (GSI) began to increase in
September and reached the highest value (10.1±1.8) in mid November, and
then decreased sharply in late November. The cultured fish had been in the
tertiary yolk stage oocyte longer then the wild fish. After the breeding
period, the cultured fish still had tertiary yolk stage oocytes in mid
November. Changes in serum levels of gonadal steroids were correlated with
ovarian development. Serum estradiol-17β (E2) level
increased in September, reached their highest levels in October and early
November (394.6±75.3 and 380.2±96.6 pg/ml, respectively), and then
decreased in mid November and in late November (P<0.05). Serum
17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) maintained low levels
(38.5±5.5-48.8±8.9 pg/ml) and was not significantly changed during the
experimental period (P>0.05). The effects of several hormones on
the maturation of follicle-enclosed oocytes were examined in vitro. 17,20β-P
and human chorionic gonadotropin (hCG) were found to have high potency to
induce maturation. When cultured fish with fully grown oocytes in the ovary
were injected with hCG at a dose of 1000 or 2000 IU/kg, all the fish matured
and ovulated. However, the number of eggs per fish was not sufficient for
mass seedling production. Considering all these results, we could infer that
the ovarian oocytes of the cultured female Korean spotted sea bass were not
matured and ovulated because of the lack of a gonadotropin surge. Moreover,
hCG treatment could induce oocyte maturation and ovulation in the cultured
fish.
(Division of Aqualife Science, Yosu National
University, Yosu Chonnam 550-749, South Korea, Tel.: +82-11-646-6701; fax:
+82-61-640-6217, e-mail: wklee@yosu.ac.kr)