Photoperiod regulates the
timing of sexual maturation, spawning, sex steroid and thyroid hormone
profiles in the Atlantic cod (Gadus morhua)
B. Norberg, Ch.L. Brown, O. Halldorsson, K.
Stensland, B.T. Björnsson-2004
Aquaculture, 229(1-4): 451-467
Abstract:
Atlantic cod of both sexes were held under four
different photoperiod regimes from age 1 year until second sexual maturation
at 3 years. Annual photoperiod cycles were compressed into 6 or 9 months,
held at 12 months, or extended to 18 months, in each case followed by one
12-month cycle (termed 6+12, 9+12, 12+12, and 18+12, respectively).
Photoperiod alterations caused shifts in the cyclic patterns of plasma
calcium, sex steroid, and thyroid hormones, and also produced correlative
changes in the timing of spawning. Initial spawning was advanced in the
compressed (6+12) photoperiod group, followed by further advancement in the
timing of the second spawning. Conversely, spawning was delayed in the 18+12
group.
Patterns in circulating hormones observed under these
experimental conditions were consistent with the coupling of photoperiod to
spawning by way of established endocrine transducers. These results
demonstrate that manipulation of the annual photoperiod cycle is a powerful
hatchery technique in the maintenance of reproductive stocks of Atlantic cod
that spawn at various times of the year.