Gonadal development and
associated changes in liver size and sexual steroids during the reproductive
cycle of captive male and female Atlantic cod (Gadus morhua L.)
R. Dahle, G.L. Taranger, Ø. Karlsen, O.S. Kjesbu, B.
Norberg-2003
Comparative Biochemistry and Physiology – Part A: Molecular &
Integrative Physiology, 136(3): 641-653
Abstract:
Gametogenesis in female and male Atlantic cod (Gadus
morhua L.) was investigated by sampling blood plasma and gonadal tissue
from 19 to 33-month-old fish. The reproductive cycles of both female and
male Atlantic cod are characterized by distinct annual variations in gonadal
size and developmental stage and these are associated with changes in sex
steroids and liver size. IH did not change during early
gonadal development, but both spent females and males had lower IH
than late maturing females and spermiating males, respectively. In females IG
was correlated to plasma E2 levels and they were highest in spawning
females. The lowest levels during the reproductive cycle were observed in
spent females. Plasma T levels were low throughout ovarian development, and
were at a minimum in spent females. 11-ketotestosterone in plasma of males
increased rapidly during spermiation, while T increased at earlier
testicular stages and reached maximum during spermiation. High plasma levels
of steroids in male and female cod during spawning serve to promote further
development and growth of less advanced stages of germ cells.